How many watts does an air conditioner use? Real numbers by BTU.
A 12,000 BTU window unit pulls about 1,050 W running. A 36,000 BTU central system pulls 3,500–4,500 W. Here's the wattage and the cost per hour for every common AC type in 2026.
Wattage formula
An AC's nameplate gives you either watts directly or BTU/hr cooling capacity and an efficiency rating. The conversion:
watts = BTU/hr ÷ EER cost_per_hour = (watts ÷ 1000) × rate
EER (Energy Efficiency Ratio) is BTU per watt at fixed test conditions. SEER and SEER2 are seasonal versions used for central systems — divide SEER by 1.1 for a rough EER equivalent.
Wattage by AC type
| Type | Typical BTU | Watts (running) | $/hour @ $0.175 |
|---|---|---|---|
| Small window unit | 5,000–6,000 | 450–550 | $0.08–$0.10 |
| Medium window | 8,000–10,000 | 700–900 | $0.12–$0.16 |
| Large window | 12,000–15,000 | 1,000–1,300 | $0.18–$0.23 |
| Portable AC | 8,000–14,000 | 900–1,500 | $0.16–$0.26 |
| Mini-split 1-zone | 9,000–18,000 | 500–1,400 | $0.09–$0.25 |
| Central 2 ton | 24,000 | 2,000–3,000 | $0.35–$0.53 |
| Central 3 ton | 36,000 | 3,000–4,500 | $0.53–$0.79 |
| Central 5 ton | 60,000 | 5,000–7,000 | $0.88–$1.23 |
Monthly cost: what you'll really pay
Hourly cost only tells half the story — your AC doesn't run 24/7. Compressor duty cycle averages 30–70% during use. Typical summer-month bill addition by climate:
- Mild summer (Pacific NW): central 3 ton, ~$50–$80/month June–August.
- Moderate (Northeast, Midwest): ~$80–$140/month June–August.
- Hot (Texas, Florida, Phoenix): ~$200–$380/month May–September. Phoenix peak bills can hit $450.
5 ways to cut AC wattage
- Raise the setpoint 2 °F. Saves ~6–10% on cooling.
- Clean the filter monthly. Dirty filter cuts efficiency by up to 15%.
- Use a smart thermostat with schedule. 5–8% savings, no comfort loss.
- Shade the outdoor condenser. 5–10% reduction in compressor load on sunny days.
- Switch to a heat pump / mini-split with inverter compressor. 30–50% less electricity than fixed-speed AC.
Run your AC through the calculator
The general electricity cost calculator takes wattage and hours and gives you daily/monthly/yearly. For whole-home electrification with a heat pump that also heats, see the heat pump calculator.
Frequently asked questions
What is EER vs SEER vs SEER2?
EER is efficiency at a fixed 95 °F test. SEER averages across a cooling season. SEER2 (mandatory since 2023) uses a more rigorous test reflecting real ductwork pressure — SEER2 ≈ SEER × 0.95.
Does running the AC longer at a higher temp save electricity?
Generally no — the more efficient strategy is to set it once at your comfort temp and let it cycle. Setbacks save energy only when the house is unoccupied for 8+ hours.
Are portable ACs really less efficient?
Yes. Portable units have a single exhaust hose that depressurizes the room, drawing in hot outside air through every gap. Real efficiency is 20–40% worse than the nameplate suggests. Window units always win on $/BTU.