How Many Watts Does an Air Conditioner Use?

A small 5,000 BTU window air conditioner uses about 450–550 watts, a mid-size 10,000 BTU unit about 900–1,100 watts, a large 12,000 BTU unit around 1,200 watts, and central air conditioning 3,000–5,000 watts. AC power consumption tracks cooling capacity, measured in BTU per hour, adjusted by the unit's efficiency rating (EER or SEER). A more efficient unit delivers the same cooling for fewer watts.

Because air conditioners are seasonal, annual kWh alone can mislead — most homes cool only about four months of the year. The calculator above reports both an annualized figure and a realistic seasonal cost over 120 days, plus the amperage so you can confirm the circuit is sized correctly. For whole-home cost, combine it with the electricity cost calculator and power consumption calculator.

The single best predictor of AC wattage is the cooling capacity in BTU/hr. As a rule of thumb, watts ≈ BTU ÷ EER, where EER (Energy Efficiency Ratio) is typically 9–12 for room units. The table below shows typical running watts and the resulting amperage at 120 V for common sizes. Larger 240 V units (18,000 BTU and up) draw fewer amps because voltage is doubled.

Use this table to match a unit to a circuit: a standard 120 V, 15-amp outlet safely supplies about 1,440 watts continuous (80% of 1,800 W), so anything above roughly a 12,000–14,000 BTU unit typically needs a dedicated 20-amp circuit or a 240 V connection.

The calculator uses:

And for the seasonal figure most people actually care about:

The 120-day season represents a typical four-month cooling period; adjust upward for hot southern climates (some run 6–8 months) or downward for mild regions. Amperage — needed to confirm your wiring and breaker — is simply Amps = Watts ÷ Voltage. A 1,200 W unit on a 120 V circuit draws 10 amps, which is why 12,000 BTU units are near the practical limit of a shared 15-amp outlet.

Two efficiency numbers govern how many watts a given BTU rating needs. EER is the steady-state ratio (BTU ÷ watts) at a fixed test condition; SEER is a seasonal average used for central systems. Higher EER/SEER means fewer watts for the same cooling — a 12,000 BTU unit at EER 12 draws 1,000 W, while the same capacity at EER 9 draws 1,333 W.

One more subtlety separates the two BTU numbers a nameplate may show. The cooling capacity in BTU/hr describes how much heat the unit removes, while the electrical input in watts describes how much power it consumes — they are related by efficiency, not equal. A 10,000 BTU unit does not use 10,000 watts; at EER 10 it uses 1,000 watts. Confusing the two leads people to wildly overestimate their bill, so always run your cost math on the input watts (or amps × volts), never on the BTU figure. When only BTU and an EER rating are printed, divide BTU by EER to recover the watts before using the calculator above, and remember that the amperage on the nameplate already reflects the true electrical draw regardless of the cooling capacity marketed on the box.

Example 1 — 12,000 BTU window unit: 1,200 W running, 8 hours a day. Daily = 1,200 × 8 ÷ 1000 = 9.6 kWh. Over a 120-day season at $0.17/kWh: 9.6 × 120 × 0.17 = $195.84 for the summer. Annualized it would be 3,504 kWh, but you only pay for the season you run it.

Example 2 — 8,000 BTU bedroom unit: 900 W, 10 hours a night. Daily = 9.0 kWh. Season = 9.0 × 120 × 0.17 = $183.60. Running it only while sleeping instead of all day roughly halves the cost versus continuous operation.

Example 3 — 3-ton central AC: 3,500 W, 6 hours of compressor runtime a day (a central system cycles). Daily = 21 kWh. Season = 21 × 120 × 0.17 = $428.40, and in a hot climate running 8 months that easily doubles. This is why raising the thermostat a few degrees and using a programmable schedule produces large savings on central systems.

Air conditioners have a compressor motor, so like refrigerators they draw a startup surge of roughly 2–4× the running current for a fraction of a second (unless the unit has an inverter/soft-start compressor, which nearly eliminates the spike). Two practical consequences:

• Circuit sizing. A 120 V, 15-amp circuit should carry no more than 12 amps continuous (the 80% rule), so units drawing above ~1,440 W need a 20-amp circuit or a 240 V connection.
• Generator/backup sizing. Size the generator for the starting watts. A soft-start kit lets you run a larger AC on a smaller generator or off-grid inverter by taming the surge.

If your unit's label lists amps rather than watts, convert with the air conditioner amps to watts tool (watts = amps × volts). For a 120 V unit, multiply amps by 120; for a 240 V unit, by 240.

1. Enter cooling watts. Read the nameplate, or estimate from BTU ÷ EER (use the table above). For central AC, use the outdoor condenser's rated watts or roughly 1,000–1,200 W per ton of cooling.
2. Enter hours per day. Estimate realistic compressor runtime, not just hours the unit is switched on — on a mild day it cycles far less than at peak heat.
3. Enter your electricity rate. Cooling loads often fall in higher tiers or peak time-of-use periods, so use your marginal summer rate for accuracy.
4. Read the results. Primary shows annualized kWh; secondary shows daily kWh, seasonal (120-day) cost, and amps at 120 V for circuit checks.

For 240 V units, the amps-at-120 V figure is a reference for comparison; divide it by two to get the actual 240 V current draw.

Cooling is often the single largest summer electricity expense. High-impact steps:

• Right-size the unit. An oversized AC short-cycles, cooling the air without removing humidity and wasting energy. Match BTU to room size (~20 BTU per square foot as a starting point).
• Raise the setpoint. Each degree higher on the thermostat cuts cooling energy by roughly 3–5%. 78°F when home and warmer when away is a common efficient target.
• Buy high EER/SEER. An EER 12 unit uses ~25% fewer watts than an EER 9 unit for the same cooling.
• Seal and shade. Weatherstrip the window kit, close blinds on sun-facing windows, and insulate — the AC only has to fight the heat that gets in.
• Use fans. A ceiling fan lets you raise the thermostat 3–4°F at a fraction of the wattage (a fan uses 15–75 W versus 1,000+ W for the AC).
• Clean the filter. A clogged filter restricts airflow and lengthens runtime; clean or replace it monthly in season.

Choosing the right cooling capacity is the difference between an efficient, comfortable room and an oversized unit that wastes energy. The Department of Energy's starting rule of thumb is about 20 BTU per square foot of living space, which is why a 5,000 BTU unit suits a 100–150 sq ft bedroom while a 12,000 BTU unit handles a 450–550 sq ft great room. But square footage is only the baseline — several adjustments matter, and each changes the watts you will ultimately draw.

Add roughly 10% for a very sunny room and subtract about 10% for a heavily shaded one. Add 600 BTU for each person who regularly occupies the space beyond two, since bodies generate heat. Increase capacity by about 4,000 BTU if the unit cools a kitchen, where the stove and refrigerator add a significant heat load. Rooms with high ceilings, poor insulation, or large west-facing windows also push the requirement up. Getting this right keeps wattage proportional to the actual cooling job.

Both oversizing and undersizing hurt efficiency. An oversized air conditioner cools the air quickly and then shuts off before it has run long enough to remove humidity, leaving the room cold and clammy and forcing frequent short-cycling that stresses the compressor and wastes the energy-hungry startup surge on every restart. An undersized unit runs continuously at full wattage, never reaching the setpoint on hot days, which drives up both energy use and your electric bill while wearing out the machine. The goal is a unit that runs in long, steady cycles — long enough to dehumidify, not so long that it never rests.

Efficiency ratings tie directly into the wattage math. A unit's EER (for room units) or SEER2 (the current standard for central systems) tells you how many BTU of cooling you get per watt. When two units carry the same BTU rating, the higher-EER model draws fewer watts to deliver identical cooling, so it costs less to run every hour of every season. Over a long cooling season the difference between an EER 9 and an EER 12 unit — about 25% fewer watts — can outweigh a modest difference in purchase price. When you shop, compare the estimated seasonal cost on the EnergyGuide label alongside the BTU rating, then plug the resulting watts into the calculator above to see the real dollars for your climate and rate.

An air conditioner is a heavy but seasonal load. Its close cousin in the opposite season is the space heater — both are high-wattage comfort appliances that run for months, not minutes, so their seasonal cost dwarfs briefly-used devices. Compared with an always-on refrigerator, an AC draws far more instantaneous power but for a limited season.

The universal way to compare is annual (or seasonal) kWh, not nameplate watts. Feed any two appliances into the appliance running cost calculator to rank them by real cost. For laundry loads, see the washing machine wattage and dryer wattage guides.