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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)
  • 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)
  • 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.

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.

Quick 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.

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