Window AC Size Calculator: What Size Window Air Conditioner Do I Need?

Window AC Size Chart by BTU and Room Size

People arrive here going one of two directions. Either you know the room and want the BTU number, or you have already seen a unit on a shelf and want to know whether it will actually cool your room. The window AC size calculator above answers the first one. The chart below and the sections under it answer the second, using the same bands the calculator uses.

One thing to know before you read it. These bands come from a load calculation rather than a single headline number, so they account for climate, ceiling height, sun, insulation, and the people and appliances in the room. From 6,000 BTU up they land within a few percent of the coverage printed on the box. The exception is the smallest unit: almost every 5,000 BTU listing claims about 150 sq ft, which works out to 33 BTU per square foot, against roughly 22 to 24 for the same brands' larger models. That is the manufacturer being cautious on the entry size, not a different calculation. Note too that the calculator matches your load to the nearest size rather than rounding up, so the unit it picks can sit a little under the calculated load on purpose. The reason for that is in the oversizing section below.

Window AC BTU Chart: The ENERGY STAR Figures Next to Ours

The table above goes by many names: window AC unit size chart, window AC unit BTU chart, window air conditioner sizing chart, or just a BTU chart for window AC units. The best known window air conditioner BTU chart is the one ENERGY STAR publishes for room air conditioners. It is worth seeing beside our own numbers, because where the two agree you can trust the answer, and where they part you should know why.

Source: ENERGY STAR, room air conditioners. Our column is the calculator run for a bedroom with two people in a mixed climate, at each end of the area range.

Up to 1,000 sq ft the two charts never sit more than one step apart. ENERGY STAR gives one size for each range and picks the size that suits the top of it, while our figures move within the range. The real gap is at the smallest size. The government chart stops 5,000 BTU at 150 sq ft, and our load calculation carries it to about 230 sq ft in a bedroom. If your small room is sunny, crowded or on the top floor, lean toward the ENERGY STAR figure.

Both charts adjust for the same things in nearly the same way. ENERGY STAR says to add 10% for a very sunny room, take 10% off for a heavily shaded one, add 600 BTU for each person beyond two and add 4,000 BTU for a kitchen. Tip: when two independent charts land on the same size, buy it. When they differ by a step, let sun and floor level decide.

Window AC BTU Per Square Foot: Is It 20, 25 or 30?

You will hear all three, and the spread matters. A 300 sq ft room is 6,000 BTU at 20 per square foot and 9,000 at 30, which is three sizes apart on the shelf. Our calculator starts from about 22 and lands near 23 to 24 BTU per square foot for a normal bedroom once two people and a mixed climate are counted. That is why 250 sq ft comes out at 6,000 and 350 sq ft at 8,000.

So the honest window air conditioner BTU per square foot figure is 20 to 25, and 30 belongs only to a room with a real extra load: a kitchen, a top floor under a hot roof, a loft, or a room above a garage. One owner did this sum for a 17 by 14 ft bedroom, got 238 sq ft and about 6,000 BTU, and doubted it because it sounded too small. It is right. A 6,000 BTU unit is what the calculator gives for that room too.

Window AC Unit Coverage: How Much Area Each Size Cools

Coverage is the number most people are actually looking for when they start shopping. It is the floor area a given capacity can hold at temperature on a design day, and it is what the chart above lists in its third column. A 5,000 BTU unit covers up to about 230 sq ft, a 10,000 covers roughly 410 to 470 sq ft, and the largest 24,000 BTU units reach about 1,175 sq ft.

Treat those figures as a starting point rather than a promise, because coverage is not a property of the air conditioner alone. The same 8,000 BTU unit that comfortably holds a shaded ground floor bedroom will struggle in a top floor room of identical size with afternoon sun and poor insulation. That is the whole reason the calculator at the top of this page asks about climate zone, ceiling height, sun and insulation instead of just square footage, and why two rooms with the same floor area can land two sizes apart.

One more thing coverage figures never account for: shape. A unit sits in one window and pushes air in one direction, so an L-shaped room, a space split by a partition, or anything with a doorway the air has to turn through will underperform its coverage rating no matter how the arithmetic works out. Square footage tells you how much heat there is to remove; it says nothing about whether one unit can reach all of it.

5000 BTU Air Conditioner Room Size: The Smallest Window Unit Sold

A 5,000 BTU window AC covers up to about 230 sq ft. It is the floor of the entire category, and that creates a situation people run into constantly. If your room is smaller than this, you cannot buy down. One owner posted about a 66 sq ft room and worried that a 5,000 unit rated for 150 sq ft would be far too big for it. It is oversized, and so is everything else on the shelf. In a room under roughly 120 sq ft, buy the 5,000 and run it on the lowest fan speed, because nothing smaller is manufactured.

6000 BTU Air Conditioner Room Size and the Overkill Question

Expect 235 to 275 sq ft out of a 6,000 BTU window AC. This is the size that produces the most second-guessing, usually from someone with a 120 sq ft room asking whether 6,000 is overkill. By the bands above it is, and not by a small margin. Does that matter much? At this end of the ladder, honestly not very. The gap between 5,000 and 6,000 is small enough that an inverter model will modulate straight through it. Two owners reported 220 and 226 sq ft bedrooms staying cool on 6,000 running on low, which sits just under the band and still works, because a bedroom at night has no sun load and almost nothing generating heat in it.

8000 BTU Air Conditioner Room Size, and Why 350 Sq Ft Is Optimistic

The 8,000 BTU size handles 320 to 360 sq ft. You will also see this exact unit advertised as covering 350 sq ft, which lands inside that band, so for once the box and the arithmetic agree. What the box cannot tell you is what else is in the room. Two owner reports show why that matters. One sized a 282 sq ft room with 8 ft ceilings and low sun, landed on 8,000, and it worked. The other put 8,000 into a 290 sq ft studio and described it as horrible and barely cooling. Eight square feet did not cause that. What separates those two rooms is what else is inside them, which is the subject of the studio section further down.

Because this size comes up so often, here are the short answers. The 8000 BTU room size, the 8000 BTU AC room size, is 320 to 360 sq ft in a bedroom. In 8000 BTU sq ft terms that is about 23 BTU for each square foot. How many square feet does 8000 BTU air conditioner cool in a hot and humid climate? About 330 at most. Is 8000 BTU enough for a living room? Yes, up to roughly 315 sq ft, because a living room carries more people and screens. For a top floor room with strong afternoon sun the limit is near 310 sq ft. It cools one room. An 8,000 BTU unit will not cool two rooms through a doorway, and it is not enough for a small apartment unless the apartment is a single open space of that size.

7000 and 9000 BTU Room Size: The Two Sizes People Skip

A 7,000 BTU window AC covers 280 to 315 sq ft and a 9,000 BTU unit covers 365 to 405 sq ft. Stores stock fewer of both, so shoppers jump from 6,000 to 8,000 or from 8,000 to 10,000 and end up a step too big. If your room sits in one of these two bands, it is worth looking for the exact size.

The 9,000 BTU size is also the answer to a question we see often: what is the 0.75 ton window AC room size? Three quarters of a ton is 9,000 BTU, so it is the same 365 to 405 sq ft, a small living room or a large studio. In a living room the 9,000 BTU limit drops to about 360 sq ft.

10000 BTU Air Conditioner Room Size in Real Apartments

A 10,000 BTU window AC covers roughly 410 to 470 sq ft on our bands. Owner reports run well above that, and this is the size where the gap between the math and real life opens widest. One owner cools a 676 sq ft open plan space in Florida on 10,000 and says it is comfortable on the low setting. Another reports 10,000 easily cooling an entire 1,000 sq ft top floor apartment. Those are owner reports rather than our calculation, and they work because open space with few interior doors behaves nothing like the same floor area cut into rooms. Size for the room the unit sits in, not the floor area on the lease.

12000 BTU Air Conditioner Room Size Where a Window Unit Hits 1 Ton

A 12,000 BTU window AC covers about 475 to 560 sq ft, and it is exactly 1 ton. So this is the rung where window units and central systems finally get described in the same language, which matters when you are comparing options. A contractor talking about 1 ton and a box on a shelf reading 12,000 BTU are the same quantity of cooling doing completely different jobs. One serves a room through a window, the other serves a house through ducts. If you need to move between the two labels at any size, our BTU to ton conversion chart lists every common step.

14000 BTU Air Conditioner Room Size for Sunny and Top Floor Rooms

565 to 635 sq ft is the 14,000 BTU band. The reason this step exists at all, wedged between 12,000 and 15,000, is that sun and floor level can move a room across a boundary without the floor area changing at all. Our engine adds 10% for heavy sun exposure and 5% for a top floor. Run the numbers on a mild climate and a 560 sq ft top floor room facing the afternoon sun comes out at 14,000, while the identical room on the ground floor with shade comes out at 10,000. When you are stuck between two sizes, the tiebreaker is sun and floor level, not square footage.

15000 BTU Air Conditioner Room Size and the Circuit It Needs

Fifteen thousand BTU reaches 640 to 740 sq ft. This is also roughly where the electrical question starts mattering more than the sizing question. Units at and above this capacity commonly want a dedicated circuit rather than sharing a bedroom outlet with everything else on that wall, and some ship with a plug shape that will not fit the receptacle under your window. Check that on the spec sheet before you buy, because it turns a same-afternoon install into an electrician visit. Our AC wattage calculator gives you the running watts, the amps, and the startup surge for any BTU rating.

18000 BTU Air Conditioner Room Size Near the Window Unit Ceiling

At 18,000 BTU you are into 745 to 1,000 sq ft territory. Two things change once you reach this size. The unit gets heavy enough that the window frame and the sill stop being an afterthought and become part of the decision, and the number of models on the market drops off sharply. Retail ranges are deep at 5,000 through 12,000 and thin above 15,000. So the practical question quietly shifts from what size do I need to what can I actually get delivered.

24000 BTU Air Conditioner Room Size: The Largest Window AC Made

A 24,000 BTU window AC covers about 1,005 to 1,175 sq ft, and it is the top of the ladder. There is no step above it. The calculator on this page flags that for you rather than hiding it: when your room load comes out past 24,000, the result tells you the room has outgrown the category instead of quietly showing you a size nobody manufactures. That warning is the single most useful thing this page can give you, so the next section is about what to do when you get it.

When Your Room Needs More Than a Window AC Can Deliver

Here is the situation that sends people round in circles, and almost nothing online addresses it directly. You measure your living room, put the numbers into a sizing tool, and it tells you that you need 20,000 to 24,000 BTU. Then you go shopping and every window unit sold for a room that size is rated 14,000. So which one is lying?

Neither, quite. One owner hit this exact wall with a 700 sq ft living room: the calculator returned 20,000 to 24,000 and the retail listings for that space said 14,000. On our bands a 700 sq ft room genuinely does need 24,000, so the calculator was right and the retail coverage rating was optimistic. Another owner was told plainly that 1,000 sq ft needs around 20,000 BTU in total and that window units are not sold that big.

So what do you do about it? There are three honest answers and not one of them is a bigger window unit.

• Split the load across two units. Two 12,000 BTU units in two windows will cool 700 sq ft better than one 24,000 unit ever could, because you are putting the air where it needs to be instead of asking one fan to throw it the length of the room.
• Cool the room you sit in, not the floor plan. If the space measures 700 sq ft only because a dining area opens off it, size for where people actually are and let the rest coast a few degrees warmer.
• Step out of the category. Past roughly 900 sq ft the honest answer is a ductless head or a central system. Our mini split size calculator covers the first and the central AC size calculator covers the second.

Tip: if the calculator hands you more than 24,000 BTU, stop looking at window units altogether, because the number you need is not made in that shape.

Two footnotes on stepping out of the category. First, if the reason you are looking at a window unit is that the room is cold in winter as well as hot in summer, there is a middle option most people never hear about: a window unit that also heats, which drops into the same opening and covers both seasons without any installation work. Second, if you are seriously weighing a ductless head instead, price it before you decide, because the equipment is only part of it. The mini split installation cost calculator shows what a single-zone system runs installed, which is the number that usually decides between one ductless head and two window units.

Is a Bigger Window AC Better?

Every window AC discussion has this question in it somewhere, usually phrased as whether there is any harm in going one size up just to be safe. Short cycling and the cold, clammy room it produces are covered in the FAQ below. What is worth adding here is the part that actually settles it, because "never oversize" is not quite true either.

Going one size up is the right call when the room carries something the square footage does not capture:

• A west or south facing window taking afternoon sun. Our engine adds 10% for heavy sun exposure.
• A top floor sitting under a hot roof, worth another 5%.
• A kitchen in the same room. That one is not a percentage, it is a flat 4,000 BTU, because appliances throw off real heat. A refrigerator alone is 600 BTU and it runs whether you are home or not.
• More than two people in the room regularly, at 400 BTU each.

Going one size up is a mistake when none of those apply. A 120 sq ft bedroom on the ground floor with a shaded window does not need 6,000 BTU because somebody said bigger is safer, and the owner who paused to ask that question about a 120 sq ft room was right to pause. Size up for a reason you can name out loud. If you cannot name one, take the smaller unit.

Studios and Open Plan Rooms Need More Than Their Square Footage Suggests

A studio breaks the chart, and the 8,000 BTU section above is where you can watch it happen. One owner put 8,000 into a 282 sq ft room and it worked fine. Another put 8,000 into a 290 sq ft studio and called it barely cooling. Eight square feet is not the difference. The difference is that a studio is a bedroom, a living room and a kitchen all sharing one volume of air.

Our engine treats that literally, and the numbers are blunt. A bedroom adds nothing on top of the envelope load. A living room adds 1,000 BTU. A kitchen adds 4,000. So a 290 sq ft studio counted honestly as a living room rather than a bedroom comes out at 10,000 BTU instead of 8,000, which is exactly the size that owner turned out to need. Count it as a kitchen, because the stove genuinely is in the same room, and it climbs further still.

For a studio, size it as the room type that generates the most heat, not the one you spend the most hours in. The same logic applies to any open plan space where a cooking area has no door on it.

Can One Window AC Cool Two Rooms?

Short answer, badly. A window AC is a fan sitting in a wall, and a doorway is a far smaller opening than the room behind it.

The clearest case from real installs is 350 sq ft split across two rooms on an 8,000 BTU unit. On floor area alone that is not wildly off. 350 sq ft sits just above our 8,000 band, so you would expect it to be marginal rather than a failure. It failed, and the advice that owner got back was 12,000 or more, and possibly two units.

Now set that against the 676 sq ft open plan space in Florida running comfortably on 10,000. Nearly twice the floor area on a smaller unit, and it works. The only thing that changed is whether the air can move.

So the number to put into the calculator is the room the unit sits in, plus any space that opens directly onto it with no door in between. Anything behind a doorway needs its own unit.

Window Air Conditioner Size by Square Feet

The bands above run by unit size. Below we have gone the other way for the room sizes people ask about most, and at the larger end the answer stops being a single unit.

Window Air Conditioner for 200, 300 and 400 Square Feet

These are the room sizes where one unit is always the answer, so the only question is which step. For 200 sq ft the calculator gives 5,000 BTU. For 250 sq ft it gives 6,000. A 300 sq ft room needs 7,000 BTU, a 400 sq ft room needs 9,000 and 450 sq ft needs 10,000. How many BTU for 360 sq ft? 8,000, the very top of that size.

All six assume a bedroom with average sun in a mixed climate. Use the next size up for a living room at the top of its band, a top floor, or a hot and humid climate. A 14 by 14 ft room, at 196 sq ft, takes 5,000 BTU. A 13 by 23 ft room, at 299 sq ft, takes 7,000.

Window Air Conditioner for 500 Square Feet

500 sq ft comes out somewhere between 12,000 and 15,000 BTU, and which end you land on depends entirely on what is in the room. Work from floor area alone and 500 sq ft is about 12,000. Put a living room's worth of people, a television and lights into it and our engine lands on 15,000, because those add roughly 2,250 BTU before the climate factor even applies. A hot and humid climate takes it to 18,000 or beyond. That is the whole reason a coverage rating printed on a box and a calculator result disagree, and it is worth knowing which one you are reading.

The other useful question at this size is whether 500 sq ft is really one room. If it is a single open living room, one unit handles it. If it is a living room with a bedroom off it, the two-room section above applies and you will be better served by a smaller unit in each.

Window Air Conditioner for 700 Square Feet

700 sq ft comes out at about 24,000 BTU, the largest window unit made, and in a hot climate it needs more than the category sells. This is the precise case one owner walked into when the calculator said 20,000 to 24,000 and every retail listing for that space insisted 14,000 was enough. Trust the calculator. Better still, split it. Two 12,000 BTU units in two windows will cool 700 sq ft more evenly than one 24,000 unit, and if one dies in August you are not left with nothing.

Window Air Conditioner 800 Square Feet: Where Two Units Beat One

At 800 sq ft the arithmetic still works. An 18,000 BTU unit covers a room that size on our bands in most climates, and a 24,000 reaches about 1,175 sq ft under mild conditions. The arithmetic is no longer the constraint here. In practice a room of that size almost never has the shape for it, because one fan cannot throw air thirty feet and around a corner. Two units sized for the halves of the space is the right answer here nearly every time, and it usually costs less than the single largest unit as well.

Window Air Conditioner for 1000 Square Feet

1,000 sq ft is past the ceiling. The load works out near 27,000 BTU in mild conditions and higher in a hot climate, while the largest window unit made is 24,000. One owner reports a single 10,000 BTU unit easily cooling a 1,000 sq ft top floor apartment, which sounds like a flat contradiction, and it is worth explaining why it is not. That unit is not holding 1,000 sq ft at a setpoint. It is cooling the room it is in and letting cooler air drift through an open plan with no doors to stop it.

If your 1,000 sq ft has bedrooms with doors on them, one unit will not do it. A second owner working the same problem was told to plan for roughly 20,000 BTU in total and that no window unit is sold that big. So the practical answer at this size is two or three units, or a ductless system. If you would rather not put anything in the window at all, the portable AC size calculator sizes a free-standing unit instead, though note that portables are rated on a different standard and lose some capacity to the exhaust hose.

Window Air Conditioner Dimensions: Will It Fit Your Window?

Size has two meanings for a window unit. The first is cooling capacity in BTU, which is everything above this line. The second is the physical size of the box and the opening it needs, and that one decides whether you can install what you bought. Window air conditioner sizes grow with capacity, so a bigger BTU number needs a wider and taller window. Window AC size dimensions are the width, height and depth of the box, and window unit dimensions or the size of a window AC on a listing are what you check against the window opening.

The table shows the window size for window AC units at each capacity, taken from one major manufacturer's published fit chart for a standard double-hung window with the supplied side panels. Other makes differ by an inch or two, so treat it as a guide to window AC window size and confirm with the manual for your model. If you are choosing a window air conditioner by window size, start here. If you are choosing a window air conditioner by dimensions of the box, use the list under the table.

Tip: choose the BTU from the room, then check the window. If the window is too small for that size, split the load across two smaller units and do not force a large one in.

Window AC Unit Dimensions by Size, in Inches

The cabinet itself is narrower than the window it needs. These are the ranges on the manufacturer spec sheets we read, width by height by depth:

• 5,000 BTU: 16.5 to 18.5 inches wide, about 12.5 inches tall, 14 to 15 inches deep, about 41 pounds. These are the smallest window AC dimensions you will find, and small window AC dimensions vary little from one make to the next.
• 8,000 BTU: 18.5 to 19 inches wide, 12.5 to 14.5 inches tall, 14.5 to 15.5 inches deep, 44 to 52 pounds.
• 12,000 BTU: 19 to 21.5 inches wide, 14.5 to 16 inches tall, 21 to 22 inches deep, 63 to 66 pounds.

So there is no single standard window AC size, and window AC unit sizes are better read from the spec sheet than guessed. Up to 8,000 BTU the units are close to one another, near 18 inches wide and 13 inches tall. From 10,000 BTU the cabinet gets taller and much deeper, and the fit chart above shows it in the bigger opening each step needs. We have not listed cabinet sizes above 12,000 BTU because we did not find enough spec sheets to give an honest range.

How to Measure a Window for an Air Conditioner

1. Width. Measure between the inside faces of the window frame, at the narrowest point, with the sash raised. This is the number to compare with the fit chart.
2. Height. Raise the lower sash as far as it goes and measure from the sill to the bottom of the sash. It must be at least the minimum opening height for the unit.
3. Sill and frame. Check that the sill is flat and solid, and look for a storm window frame that stands higher than the sill, because the unit has to clear it.
4. Outlet. Find the nearest outlet and note whether it is a normal one. Units of about 15,000 BTU and up can need a different receptacle.

A narrow window is not always the end of it. Most units can go into a window slimmer than the chart says if you leave the side panels off, as long as the opening is wider than the cabinet. That is how a 5,000 BTU unit goes into a window about 20 inches wide. A window wider than the panels reach needs a filler panel, which the FAQ below covers.

Basement Window Air Conditioner: Why the Window Shape Decides It

Cooling a basement is a different job from cooling a room upstairs, and almost none of the difficulty is about BTU. A basement is already the coolest part of the house. The problems are the window, the damp, and the water.

Start with the window, because it settles everything else. A standard window air conditioner needs a double-hung sash that slides up and leaves a rectangular opening the unit can sit in. Basements rarely have one. What they usually have is a hopper window that tips inward from the top, or a horizontal slider. Neither gives you the opening a normal unit is built for, which is why so many people buy a correctly sized unit and then find it will not physically go in.

AC Units for Basement Windows: What Actually Fits

Match the unit to the window type rather than the other way round:

• Hopper window. The sash tips inward and blocks the opening, so a standard unit cannot mount. A vertical or casement-style unit is designed for this shape, or you vent a portable through the gap with a fitted panel.
• Horizontal slider. Same problem rotated. A vertical unit built for sliders fits; a standard one does not, and propping one in place is how units end up falling out.
• Small double-hung. The one easy case. Check the unit's minimum window width, not its own width, because the side panels need somewhere to sit.
• No usable window at all. Then it is a ductless head or nothing, and a portable will not save you because it still needs somewhere to put the hose.

One thing to check before buying anything: if the basement is finished and that window is the egress, you cannot block it. Building codes require a bedroom below grade to have an unobstructed escape route, and a wedged-in air conditioner obstructs it.

Air Conditioner for a Basement Window: What Size and Why It Is Smaller

Size a basement below what the square footage suggests. Surrounding earth holds a steady temperature year round, so the walls are not gaining heat the way an above-ground room does, and there is usually little or no direct sun. A 600 sq ft basement often behaves like a 400 sq ft room upstairs.

The trap is oversizing. Put a unit sized for the floor area into a space with a small heat load and it satisfies the thermostat in minutes, shuts off, and never runs long enough to pull moisture out. In a basement that is the worst possible outcome, because moisture is the actual complaint. A cold clammy basement is a sign of too much capacity, not too little.

The Damp and the Drainage Nobody Plans For

An air conditioner does dehumidify while it runs, but a basement usually needs more moisture removed than its small cooling load will ever justify running for. If the room feels muggy rather than hot, cooling is the wrong tool and our dehumidifier size calculator is the right one. Plenty of basements need a dehumidifier and no air conditioner at all.

Then there is the water the unit itself makes. Above ground a window unit tilts slightly and drips outside, and when the tilt is wrong you get a window AC leaking water inside instead. Below grade there is often nowhere for it to drip to, because the outside of that window is a window well that sits lower than the sill. Work out where the condensate goes before you install, not after, whether that means a drain line to a floor drain, a condensate pump, or a model that collects internally.

If none of this is solvable, ductless is the honest alternative: it needs only a three-inch hole rather than a window, it modulates down far enough to run continuously at low output, and that long steady runtime is what actually dries a basement out. Our mini split size calculator sizes one.