How many watts does an air conditioner use? It depends on size and type. A small window unit can run on around 500W, while a 3-ton central AC can pull 3,000W or more. The startup surge matters as much as the running watts when you’re sizing backup power.
Electrical work can be dangerous: follow the manual, fuse and size every cable correctly, and use a licensed electrician for anything connected to household wiring.
How Many Watts Does an Air Conditioner Use? Typical Ranges
| Type | Size | Running watts | Startup surge |
|---|---|---|---|
| Window AC | 5,000–8,000 BTU | 450–800W | 1,200–2,500W |
| Window AC | 10,000–12,000 BTU | 900–1,300W | 2,500–3,500W |
| Portable AC | 8,000–14,000 BTU | 800–1,400W | 2,000–3,500W |
| Ductless mini-split (inverter) | 9,000–12,000 BTU | 300–1,200W (variable) | Low (soft start) |
| Central AC | 2–3 ton | 1,800–3,500W | Often 60–120A LRA at 240V |
| RV rooftop AC | 13,500–15,000 BTU | 1,200–1,700W | 2,500–3,500W+ |
Typical ranges, not measurements of a specific model. Check the nameplate, the EnergyGuide label, or the LRA rating on the outdoor unit.
Using EER to Estimate Watts
Watts ≈ BTU/h ÷ EER. Example math: a 10,000 BTU window unit with an EER of 11 uses about 910W while the compressor runs.
Why Inverter Mini-Splits Are Backup-Friendly
Variable-speed compressors ramp up slowly, with no big startup surge, and run at partial power most of the time. That’s why mini-splits are often the easiest AC to run from batteries or solar.
Taming Startup Surge
- Soft starters (such as Micro-Air EasyStart-style devices) can cut AC startup current a lot, which helps generators, RVs and home batteries
- Check the LRA: compare your AC’s locked-rotor amps with the inverter’s or battery’s motor-starting rating
Runtime on Batteries
Example math, 10,000 BTU window unit at 900W running and a 50% duty cycle (~450W average):
| Usable battery | Runtime |
|---|---|
| 2 kWh | ~4 hours |
| 5 kWh | ~11 hours |
| 13.5 kWh | ~30 hours (AC only) |
Hot days push duty cycle toward 100%, which halves these.
Worked Example: Running a Window AC From a Battery
Illustrative unit: 8,000 BTU window AC with a label EER of 12.
| Step | Math | Result |
|---|---|---|
| Running watts | 8,000 ÷ 12 | about 667W |
| Duty cycle on a warm evening (assumed) | 60% | about 400W average |
| Battery draw through inverter (assume 90%) | 400 ÷ 0.9 | about 444W |
| Runtime on 5kWh usable | 5,000 ÷ 444 | about 11 hours |
| Startup surge (check LRA on the label) | several times running watts on fixed-speed units |
Inverter sizing has to cover that startup, which is why surge watts vs running watts matters. EER is BTU per hour ÷ watts, a definition used on ENERGY STAR and DOE efficiency labels.
Typical Ranges by Type
| Type | Size | Typical running watts |
|---|---|---|
| Small window AC | 5,000–6,000 BTU | about 450–600W |
| Mid window AC | 8,000–12,000 BTU | about 650–1,100W |
| Portable AC | 8,000–14,000 BTU | about 900–1,400W |
| Ductless mini-split (inverter) | 9,000–12,000 BTU | about 300–1,100W (varies with speed) |
| Central AC | 3 tons (36,000 BTU) | about 2,500–3,500W |
Typical ranges; your unit’s label shows rated watts or amps and EER/CEER.
SEER2 vs EER
- EER: efficiency at one hot test condition. Best for estimating peak watts.
- SEER2: seasonal efficiency over a range of temperatures, used for central AC and heat pumps under DOE’s 2023 test procedure.
- CEER: used for room air conditioners and includes standby power.
Matching an AC to Backup Power
- Read rated watts, or amps × volts, from the label.
- Find LRA or ask the maker for startup current.
- Choose an inverter or home battery with a continuous rating above running watts and a surge rating above startup.
- Size the battery for hours of use. See how many batteries to power a house.
- Consider a soft starter for fixed-speed units.
240V Central AC
Central systems run on 240V split-phase. Illustrative: 3,000W ÷ 240V = 12.5A per leg running. The outdoor unit’s MCA and MOP numbers set the wire and breaker size. See 120V vs 240V split phase.
FAQ
How many watts does a 5,000 BTU AC use?
Usually about 450–550W running.
Can a power station run an air conditioner?
Small window units and mini-splits, often yes, if the inverter handles the surge. Central AC needs a home battery or generator.
How many amps does a window AC use?
About 4–11A at 120V, depending on size.
How many watts does a 12,000 BTU mini-split use?
At an assumed EER of 12, about 1,000W at full output, and much less at low speed.
Can solar run an air conditioner?
Yes, with enough panels and battery; daytime cooling lines up well with solar production.
Sources: U.S. Department of Energy, “Estimating Appliance and Home Electronic Energy Use” and room air conditioner guidance; ENERGY STAR; ENERGY STAR room air conditioner specifications; U.S. DOE appliance test procedures. Accessed Oct 2026.
Related: BougeRV PC35 Portable Air Conditioner Review, EcoFlow Delta 3 Max RV Air Conditioner