A window air conditioner draws roughly 4 to 10 amps on a standard 120V household circuit, a portable air conditioner draws about 8 to 13 amps on that same 120V circuit, and a central air conditioning system draws 15 to 20 amps on a dedicated 240V circuit. Ductless mini-splits sit in between, from around 5 amps for a small single-zone unit up to 17 amps for a large multi-zone system, depending on whether it is wired for 120V or 208-240V. The exact figure for any one unit depends on its BTU rating and its efficiency, and none of these numbers include the brief startup surge every compressor pulls the moment it switches on – which is usually the number that actually matters.
The table below works through the watts-to-amps arithmetic for each category, using typical BTU ratings and efficiency figures for each type.
| Unit type | Typical size | Running watts | Voltage | Running amps |
|---|---|---|---|---|
| Small window AC | 5,000 BTU | 460 W | 120 V | 3.8 A |
| Large window AC | 12,000 BTU | 1,200 W | 120 V | 10.0 A |
| Portable AC | 12,000 BTU (rated) | 1,400 W | 120 V | 11.7 A |
| Small single-zone mini-split | 9,000 BTU | 600 W | 120 V | 5.0 A |
| Large multi-zone mini-split | 48,000 BTU (4-zone) | 4,000 W | 230 V | 17.4 A |
| Central AC, 3 ton | 36,000 BTU | 3,600 W | 240 V | 15.0 A |
| Central AC, 5 ton | 60,000 BTU | 4,800 W | 240 V | 20.0 A |
From BTU to amps: the arithmetic
Air conditioners are rated in BTU per hour, a measure of heat removed, not electricity consumed. To get the electrical draw, divide the BTU rating by the unit’s EER (Energy Efficiency Ratio): watts = BTU ÷ EER. A 12,000 BTU window unit rated EER 10 draws 12,000 ÷ 10 = 1,200 W. At 120V, amps = watts ÷ volts, so 1,200 ÷ 120 = 10.0 A – the figure in the table above. A more efficient unit with the same cooling output draws fewer amps: a 12,000 BTU unit rated EER 14 draws only 857 W, or 7.1 A. Use our watts-to-amps calculator to run the numbers for a specific model once you have its wattage or amperage off the nameplate.
Central air runs on 240V – window and portable units do not
Only large, fixed appliances on a dedicated circuit run at 240V in a US home, and a central air conditioner’s outdoor condensing unit is one of them. That is why a central system pulling 3,600-4,800 W shows up as only 15-20 A rather than 30-40 A: doubling the voltage halves the current for the same power. The indoor air handler or furnace blower is usually wired as a separate 120V circuit and draws only 3-5 A on its own, so it is not folded into the condensing unit’s nameplate figure. Window units, portable units, and most small single-zone mini-splits plug into or are wired to an ordinary 120V circuit; only larger mini-split condensers, like the multi-zone example in the table, are wired for 208-240V.
Locked rotor amps: the number that actually decides whether it will start
The running amps in the table are steady-state – what the compressor pulls once it is spinning normally. For a fraction of a second at startup, the motor is momentarily stalled against refrigerant pressure and pulls 3 to 5 times that figure. This is the locked rotor amps (LRA) rating stamped on the compressor’s nameplate alongside its running load amps (RLA). A compressor with a steady 14 A running load commonly has an LRA of 45-70 A. That spike lasts well under a second, but it is what trips an undersized breaker, stalls a small generator, and overloads an inverter that was only sized for the running wattage. If you are working out whether a generator, inverter, or power station can start a particular air conditioner, the LRA figure is the one that matters, not the running watts – the same startup behaviour covered for compressor-driven appliances in our refrigerator wattage guide.
Sizing the breaker
NEC 210.20 caps a circuit at 80% of its rating for a continuous load, so a 15 A circuit carries 12 A continuous and a 20 A circuit carries 16 A. The large window unit in the table, at 10.0 A running, leaves only 2 A of headroom on a 15 A circuit – enough for very little else on the same line, which is why manufacturers usually specify a dedicated circuit for anything above about 7,500 BTU. A central air conditioner’s dedicated 240V circuit is sized by the installer from the nameplate’s minimum circuit ampacity (MCA), a figure that already accounts for the compressor’s starting behaviour rather than just its running watts, so it is not something to size from the running amps yourself.
Soft-start kits: the real answer for running AC off a battery or a small generator
A soft-start kit – sold under names like SoftStartRV and Micro-Air EasyStart – replaces the compressor’s start capacitor with one that ramps the motor up over roughly two seconds instead of slamming it to full speed instantly. Stretching the same startup work over a longer window cuts the peak LRA draw by around 65-75%. A compressor with a 45 A LRA can come down to 12-15 A of peak draw with a kit fitted, which is the difference between an air conditioner a small inverter or generator can start and one it cannot. This is the standard fix for running RV rooftop units and small mini-splits from battery power, and it is worth budgeting for before sizing anything for off-grid RV or cabin use.
Can a portable power station run an air conditioner?
Central air is out of reach for any battery-based power station: the load is thousands of continuous watts on a 240V circuit, and every power station on the market outputs 120V only. Window units, portable units, and the smaller mini-splits are a different matter. Two figures have to clear the station’s spec sheet – the unit’s running watts against the station’s continuous AC output, and its LRA spike against the station’s separate, higher surge rating. Apex 300 Versatile Power Station outputs about 3,800 W continuous with enough surge headroom to start most window units up to the 12,000 BTU / 10 A size in the table without a soft-start kit; it holds 2,765 Wh of capacity and lists at $1,899 – see our Apex 300 Versatile Power StationCheck price at BLUETTI for the full breakdown. EcoFlow DELTA Pro Solar Generator (PV400W) runs about 4,500 W continuous, for $2,399 and 3,000 Wh of capacity. For a smaller window unit, or a mini-split fitted with a soft-start kit, BLUETTI AC200L Portable Power Station outputs around 2,400 W for $899 and 2,048 Wh, and the more compact BLUETTI AC180P Portable Power Station outputs about 1,800 W for $649 and 1,440 Wh – enough for the small window and mini-split units at the top of this page, provided the compressor’s LRA is inside its surge rating. Whichever size fits the load, check the cost per watt-hour on our power station price index before buying, since sticker price alone is a poor guide to value at this capacity, and use the power station finder to match a unit to the actual wattage figures here rather than the marketing name on the box.
None of this changes the arithmetic at the top of this page: watts divided by volts gives amps, running amps are not starting amps, and central air is a 240V load a portable power station cannot touch. For the wattage of everything else in the house, see the appliance wattage chart.
How this page makes money. Some links here are affiliate links and we earn a commission if you buy through them — currently BLUETTI, ALLPOWERS, Mango Power, Renogy and MoonCool. Every other brand on this page is here because leaving it out would make the comparison useless to you, and we are paid nothing either way. Prices are each maker’s own list price at the time of writing and change often.