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AC Wattage Calculator: Watts, Amps & Cost to Run

Real EER2 math, not flat per-ton guesses: get your air conditioner's running watts, amps, startup surge, generator size, and exactly what it costs per hour, day, and month at your electricity rate.

AC Wattage & Running Cost Calculator

Watts, amps, generator size, and what it costs you per month

2026 US average is about $0.17/kWh - check your utility bill.

8 h/day is typical in peak summer; hot climates run 10-14 h.

Estimated running draw
3,070 watts
3.07 kW · 12.8 amps @ 240V · EER2 used: 11.7
Cost per hour
$0.46
Per day (8 h)
$3.65
Per month
$110
Cooling season (4 mo)
$438
Energy use21.5 kWh/day · 645 kWh/month
Startup surge (LRA)9,211 - 15,352 W for a split second
Generator needed17,000 W (or 5,500 W with a soft start)

Multiplying 3,070 watts by your hours gives a higher figure than the energy row above, and that is deliberate. The wattage is the draw at full tilt on a design day, worked out from EER2. The energy figure uses SEER2, the seasonal rating, because a compressor does not run flat out all day: it cycles, and it spends most of the season in milder conditions than the one the wattage is rated at. For a bill estimate the seasonal number is the honest one.

  • Efficiency estimated from system age: ~13.4 SEER2 equivalent.

How AC Wattage Is Actually Calculated

Most wattage charts just assign a flat number per ton. The real physics is one division:

  • Running watts = cooling BTU ÷ EER2 (the steady-state efficiency rating at 95°F)
  • EER2 from SEER2: EER2 ≈ SEER2 × 0.875 for single-stage equipment
  • Amps = watts ÷ volts (240V for central and mini split, 115V for window and portable). Many smaller ductless heads run on 115V too, so our mini split size calculator is worth running to see which capacity your room needs before you plan the circuit.
  • Energy cost: kWh = (BTU × hours) ÷ (SEER2 × 1,000) - the seasonal rating is the right one for bills because it already averages part-load performance

That's why efficiency matters as much as size: a 3-ton system can draw anywhere from 2,900 watts (new 14.3 SEER2) to 4,300 watts (1990s SEER 10) for the exact same cooling. One caution on units: this page is about electrical watts consumed. Converting a BTU rating itself into thermal watts of cooling capacity is a different calculation - that's what the BTU to watts converter does.

AC Wattage by Tonnage Chart

Running draw for modern equipment at the 2023 federal-minimum 14.3 SEER2 (≈ 12.5 EER2). Older systems draw 20-45% more - use the calculator above with your system's age for a closer number. These figures cover the outdoor unit and the indoor blower together, and the blower's share tracks how much air it has to move, which our room CFM calculator works out per room and per ton.

AC SizeRunning WattskWAmps @ 240VGenerator (no soft start)
1 ton (12,000 BTU)960 W1 kW4 A5,500 W
1.5 tons (18,000 BTU)1,440 W1.4 kW6 A8,000 W
2 tons (24,000 BTU)1,920 W1.9 kW8 A10,500 W
2.5 tons (30,000 BTU)2,400 W2.4 kW10 A13,000 W
3 tons (36,000 BTU)2,880 W2.9 kW12 A16,000 W
3.5 tons (42,000 BTU)3,360 W3.4 kW14 A18,500 W
4 tons (48,000 BTU)3,840 W3.8 kW16 A21,000 W
5 tons (60,000 BTU)4,800 W4.8 kW20 A26,500 W

Not sure what tonnage you have? Read it off the outdoor unit with our tonnage-by-model-number guide, or convert with the ton to BTU converter.

AC Amps Calculator: How Many Amps Does an Air Conditioner Use

The calculator above is already an AC amps calculator and almost nobody notices. Pick your system type and it returns running amps at the correct voltage for that type, because the dropdown is doing more than labelling: Window AC (115V) and Portable AC (115V) get divided by 115, Central AC (240V) and Mini split (240V) get divided by 240. So the same BTU number lands on two very different current figures depending on what the box is.

That is the part people trip over when they move from a central system to a room unit. Basically, halving the voltage doubles the current for identical cooling. A window unit pulling 8.8 amps is not working harder than a ductless head pulling 4 amps, it is just doing the same job on a thinner circuit.

Running amps and calculated breaker size for BTU-rated window and portable air conditioners
Unit SizeRunning WattsAmps @ 115VAmps @ 230VCircuit Sold OnCalculated Breaker
5,000 BTU425 W3.7 Anot sold115V15 A
6,000 BTU510 W4.4 Anot sold115V15 A
8,000 BTU680 W5.9 Anot sold115V15 A
10,000 BTU845 W7.4 Anot sold115V15 A
12,000 BTU1,015 W8.8 Anot sold115V15 A
15,000 BTU1,365 W11.9 A5.9 A115V or 230V15 A
18,000 BTU1,635 W14.2 A7.1 A115V or 230V20 A
24,000 BTU2,355 Wnot sold10.2 A230V15 A

Room units are rated in CEER rather than SEER2, and that rating slides down as capacity climbs, which is why the amps column rises a little faster than the BTU column does. Now the specific questions people actually type. How many amps does a 5000 BTU air conditioner use is 3.7 amps, the smallest draw of any cooling appliance you can buy. How many amps does a 12000 BTU air conditioner use is 8.8 amps on 115V. Across the full range, how many amps does a window ac unit use has no single answer: it runs from 3.7 amps at the bottom to 14.2 amps at 18,000 BTU, a four-fold spread.

How many amps does a mini split use surprises people going the other way. A 12,000 BTU inverter head on 240V draws roughly 4 amps while running, and a 36,000 BTU system about 12 amps. That is less current than a hair dryer for the smaller head, because the voltage is doubled and an inverter is not slamming a compressor on and off at full tilt. Converting btu to amps yourself is the same two steps every time: divide BTU by the efficiency rating to get watts, then divide watts by the circuit voltage.

Here is the number that actually decides things. A standard 15 amp household circuit is only rated for 12 amps of continuous load, and air conditioning counts as continuous. Read down the 115V column against that 12 amp ceiling and the pattern jumps out: everything up to 12,000 BTU fits with headroom to share, 15,000 BTU at 11.9 amps consumes the entire circuit on its own, and 18,000 BTU on 115V does not fit at all. Twelve thousand BTU is the practical ceiling for a room unit that shares a circuit with anything else, and that limit is set by your wiring rather than by the air conditioner.

What Size Breaker for an Air Conditioner

The calculated answer is the continuous load rule: take running amps, multiply by 1.25, and round up to the next standard breaker. That is the Calculated Breaker column above. For a 5,000 through 15,000 BTU room unit it lands on 15 amps, and 18,000 BTU on 115V pushes it to 20 amps.

But here is the thing some people miss, and it catches out a few electricians too. Run that same arithmetic on a mini split and the numbers look absurd. A 12,000 BTU head drawing 4 amps calculates to a 15 amp breaker, yet the installation manual calls for a 20 amp breaker on 12 AWG wire. Nothing is wrong with either figure. The breaker follows the minimum circuit ampacity stamped on the data plate, never your calculated running amps.MCA is a manufacturer number that already builds in compressor inrush, the 125% factor, and the outdoor unit's defrost and crankcase heater loads, and it is normally the larger of the two by a wide margin.

So mini split breaker size and what size breaker for mini split have a slightly frustrating but correct answer: it is printed on your unit. In practice a single-zone head lands on a 20 amp breaker for mini split installs at 9,000 and 12,000 BTU, 25 to 30 amps at 18,000 and 24,000 BTU, and a multi-zone outdoor unit can want 40 amps or more. 12000 BTU mini split breaker size is the most searched of these and comes out at 20 amps on almost every model sold.

Mini split wire size then follows the breaker rather than the draw: 14 AWG on a 15 amp circuit, 12 AWG on 20 amps, 10 AWG on 30 amps, and heavier again beyond that or on a long run where voltage drop starts to bite. So use the table above to check whether the circuit you already have can take the unit at all, then wire to the data plate and not to any calculator, ours included.

115V vs 220V Air Conditioners: Which One You Actually Get

Let me clear up the naming first, because that is most of the confusion. There are only two residential circuits, and each one goes by three names. 110V, 115V and 120V all mean the same standard outlet. 220V, 230V and 240V all mean the same double-pole circuit. Grid voltage crept upward over the decades while nameplates and habits did not, so an older unit says 110V, a spec sheet says 115V, and your utility delivers 120V, all describing one circuit. If a listing says 115V and your outlet is 120V they are compatible, and nothing needs converting.

Which one you end up with is decided by capacity, and you get less choice than you would expect. Room units through 12,000 BTU are 115V without exception. At 15,000 and 18,000 BTU both versions exist and you have to check the spec sheet. At 24,000 BTU it is 230V only. Ductless heads split at a similar point, with 9,000 BTU and many 12,000 BTU units on 115V and anything larger on 208/240V. Central systems offer no choice at all, which is exactly why nobody searches this question about them.

Now the part that decides a purchase, and it is not the running cost, because both circuits bill at the same rate per kilowatt hour. It is the install. A 115V unit plugs into the outlet already sitting under the window and you are cooling the room this afternoon. A 230V unit needs a double-pole breaker and a receptacle whose blade pattern will not physically accept a standard plug, so you are booking an electrician and waiting on their calendar. That gap is usually worth more than one step of BTU capacity, so when you are choosing between a 15,000 BTU model on 115V and the same capacity on 230V, take the one that matches the outlet you already have.

One warning worth stating plainly. Do not try to adapt between the two. Connecting a 115V unit to a 230V circuit destroys it on the spot, and no plug adapter makes a 230V unit run on a standard outlet, because the circuit itself simply carries half the voltage. If you want a particular capacity on the circuit you already own, size the room properly first with our window AC size calculator or check what a ductless head needs using the room-by-room ductless sizing tool, then match the voltage to the outlet rather than the other way round.

Short Answers by System Size

How many watts does a 1.5-ton AC use?

About 1,440 running watts (1.4 kW, 6 amps at 240V) for a modern 14.3 SEER2 unit. Running 8 hours a day at $0.17/kWh costs roughly $51 a month. Older 1.5-ton units draw 1,800-2,200 watts.

How many watts does a 2-ton AC use?

About 1,920 running watts (1.9 kW, 8 amps at 240V) for new equipment - roughly $69 a month at 8 hours/day and $0.17/kWh. A pre-2006 2-ton system pulls closer to 2,900 watts.

How many watts does a 3-ton AC use?

About 2,880 running watts (2.9 kW, 12 amps at 240V) at 14.3 SEER2 - the most common whole-house size, costing about $103 a month at typical summer runtime. Startup surge runs 8,600-14,400 watts, which is why 3-ton units need either a large standby generator or a soft-start kit.

How many watts does a 4-ton AC use?

About 3,840 running watts (3.8 kW, 16 amps at 240V) for modern equipment - roughly $137 a month at 8 hours/day. If your 4-ton short-cycles instead of running steadily, it may be oversized: check it against a whole-house load calculation.

How many watts does a 5-ton AC use?

About 4,800 running watts (4.8 kW, 20 amps at 240V) - around $171 a month at 8 hours/day and $0.17/kWh. At this size, efficiency upgrades pay back fast: dropping from SEER 10 to 16 SEER2 saves over $700 per cooling season in a hot climate.

Window and Portable AC Wattage

Room units plug into ordinary 115V outlets, which caps them around 15 amps (~1,700 watts). Typical draws: a 5,000 BTU window unit uses 400-450 watts, an 8,000 BTU about 650-700 watts, a 10,000 BTU about 800-900 watts, and a 12,000 BTU about 1,000-1,100 watts. Portables run 10-20% higher per delivered BTU because the exhaust duct radiates heat back into the room - the same reason the DOE created the SACC rating. Size the unit first with the window AC BTU calculator or portable AC calculator, then check its wattage here.

Generator Sizing: Surge Is What Matters

A compressor draws 3-5× its running watts for a fraction of a second at every start (the LRA on the data plate). A generator that can't cover that spike stalls even though it handles the running load fine. Two ways out: buy a generator sized for the surge column in the chart above, or install a soft-start kit (~$300-400 installed), which ramps the compressor up gradually and typically cuts the required generator size by half or more - a 3-ton central AC drops from a ~16,000W standby unit to a ~5,000W portable generator. It's the same trick that lets RVers run a 13,500 BTU rooftop unit on a 2,200W inverter generator, as covered in our RV AC calculator.

Cutting the Bill: Efficiency Is the Lever

Because watts = BTU ÷ EER2, the only two ways to spend less are to need fewer BTU (shade, insulation, higher thermostat setting, sealed ducts) or to buy each BTU cheaper (higher efficiency). If your system predates 2015, run the numbers in the SEER savings calculator - and if a contractor quotes a replacement, sanity-check the price with the HVAC replacement cost calculator and the size with a load calculation before signing.

Frequently Asked Questions

How many watts does an air conditioner use?
Divide the unit's cooling BTU by its EER2 rating. A modern 3-ton (36,000 BTU) central AC at the federal-minimum 14.3 SEER2 (about 12.5 EER2) draws roughly 2,880 running watts. Older systems draw much more: the same 3 tons at a 2005-era SEER 10 pulls about 4,300 watts. Window units run 400-1,400 watts and portables 700-1,500 watts depending on size.
How many watts does a 3-ton AC unit use?
A new 3-ton central AC (14.3 SEER2) draws about 2,900 running watts - roughly 12 amps at 240V. A 2015-2022 unit draws around 3,100 watts, and a pre-2006 unit closer to 4,300 watts. Startup surge is 3-5× that for a split second, which is why generator sizing is about surge, not running watts.
How many amps does a central air conditioner use?
Running amps = watts ÷ 240V. Typical modern systems: 2 tons ≈ 8 amps, 3 tons ≈ 12 amps, 4 tons ≈ 16 amps, 5 tons ≈ 20 amps. The breaker is sized larger than this (a 3-ton unit typically sits on a 25-30A circuit) because it must tolerate the startup inrush. Check the condenser's data plate for the exact MCA (minimum circuit ampacity).
How many kilowatts is a 1.5-ton AC?
About 1.4 kW of electrical draw for a modern 14.3 SEER2 unit (18,000 BTU ÷ 12.5 EER2 ≈ 1,440 watts). An older 1.5-ton unit can pull 2+ kW. Note the distinction: 1.5 tons of cooling equals 5.3 kW of thermal heat-removal capacity, but the compressor only consumes about 1.4 kW of electricity to move that heat - that ratio is exactly what the EER measures.
How do I convert AC tons to electrical kW?
Electrical draw in kW = (tons × 12,000) ÷ (EER2 × 1,000). At the modern-minimum 12.5 EER2, that's about 0.96 kW per ton - so a quick rule is roughly 1 kW of electricity per ton of cooling for new equipment, and up to 1.4 kW per ton for old SEER-10 systems.
Does an air conditioner use a lot of electricity?
It's usually the single largest electrical load in a US home. A 3-ton central AC running 8 hours a day uses about 600 kWh a month - around $100 at the 2026 average rate of $0.17/kWh, and double that in hot climates with long runtimes or expensive power. Heating and cooling together account for roughly half of a typical home's energy bill.
How much does it cost to run an AC per hour?
Cost per hour = (BTU ÷ (SEER2 × 1,000)) × your electricity rate. A modern 3-ton system at $0.17/kWh costs about $0.43 per hour of compressor runtime. A 12,000 BTU window unit costs about $0.14-0.18 per hour, and a 10,000 BTU portable about $0.15-0.20 because portables lose efficiency to duct heat gain.
How much does central AC cost per month?
At the 2026 US average of $0.17/kWh and 8 hours of daily compressor runtime: about $70/month for 2 tons, $100-105 for 3 tons, and $170 for 5 tons with modern equipment. Old SEER-10 systems cost 40-50% more for the same cooling - which is why the payback math in our SEER savings calculator often favors replacement.
What size generator do I need to run my AC?
Size for the startup surge, not running watts. A 3-ton central AC drawing 2,900 running watts can spike to 8,600-14,400 watts at compressor start, so you'd want a 16,000-watt (16 kW) standby generator to start it cold - or add a soft-start kit, which cuts inrush enough that a 5,000-watt portable generator can handle the same unit. Window units are easier: a 10,000 BTU window AC starts fine on a 2,500-3,000 watt generator.
What is the difference between running watts and starting watts?
Running watts is the steady draw while the compressor is cruising. Starting watts (locked-rotor amps, LRA) is the brief inrush - typically 3-5× running - needed to get the compressor spinning from a dead stop. It lasts under a second but trips undersized generators and dims lights. Soft-start devices and inverter-driven compressors (mini splits) largely eliminate the spike.
How can I reduce my AC's power consumption?
In order of impact: fix airflow and refrigerant charge (a dirty coil or low charge can add 20-30% to draw), raise the thermostat a few degrees (each degree saves roughly 3% on cooling energy), shade the condenser and clean its coil, seal duct leaks, and - the big one - upgrade old SEER-10 equipment, which cuts wattage by 40%+ for the same cooling. Right-sizing matters too: an oversized unit short-cycles, and starts are the most power-hungry moment.
How many tons is my AC if I know the watts?
Work the formula backwards: tons ≈ (watts × EER2) ÷ 12,000. A unit drawing 3,500 watts at roughly 12.5 EER2 is about 3.6 tons - call it a 3.5-ton system. But nameplate data is more reliable: our tonnage-by-model-number guide shows how to read the size directly off the outdoor unit's label.
How many amps does a 5,000 BTU air conditioner use?
About 3.7 amps on a 115V circuit, from roughly 425 running watts. That is the smallest draw of any air conditioner sold, and it is the one size you can run on a shared bedroom circuit without thinking about it. Step up through the range and a 10,000 BTU unit pulls about 7.4 amps and a 12,000 BTU unit about 8.8 amps, all still on a standard outlet.
What size breaker do I need for a mini split?
Whatever the data plate says, which is normally 20 amps for a 9,000 or 12,000 BTU single-zone head and 25 to 30 amps at 18,000 to 24,000 BTU. Do not size it from running amps: a 12,000 BTU head only draws about 4 amps while running, but the minimum circuit ampacity on the plate accounts for compressor inrush and the outdoor unit's auxiliary loads, so it lands far higher. Wire follows the breaker, so 12 AWG on a 20 amp circuit and 10 AWG on 30 amps.
Are 110V, 115V and 120V air conditioners the same thing?
Yes, all three names describe the standard household outlet, and 220V, 230V and 240V likewise all describe the same double-pole circuit. Grid voltage rose over the decades while product labels kept the older numbers, so a unit marked 115V plugs straight into a 120V outlet with nothing to convert. The only distinction that matters when buying is which of the two circuits the unit needs, not which name the spec sheet uses for it.
Can I convert a 220V air conditioner to run on 115V?
No, and no adapter exists that would do it, because the circuit itself supplies half the voltage rather than the plug being the obstacle. The realistic options are buying the 115V version of the same capacity where one is made, which is possible up to 18,000 BTU, or having an electrician run a 230V circuit. Connecting a 115V unit to 230V goes the other way and destroys it immediately, so check the nameplate before anything gets wired.

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