AC Running Cost Calculator
See what your air conditioner costs to run — the kW it draws, the kWh it uses and the dollar cost — from its BTU capacity, EER and your own electricity rate.
Calculator
A 36,000 BTU/h AC at EER 12.0 draws 3.00 kW ≈ $3.60 for 8.0 h at your $0.150/kWh rate.
Air-conditioner running cost is simple physics: the unit turns a set number of BTU of cooling into an electrical draw, and you pay for that draw at your local rate. The only three things that move the number are the capacity (how many BTU/h it delivers), the efficiency (its EER — how much cooling you get per watt) and the price of a kilowatt-hour where you live. This calculator asks for exactly those, plus how long the compressor actually runs, and returns the cost with the kW draw and kWh consumed shown alongside so the arithmetic is transparent.
Because the rate is your number, the result stays correct forever — there is no energy tariff baked into the page that could go stale. Pull the all-in price per kWh from your bill (divide the total bill by the kWh used to capture delivery charges, not just the headline supply rate) and the estimate will track your real cost. For seasonal figures, use your typical daily compressor hours and multiply out.
Formula
Electrical draw and cost come from the EER definition (cooling delivered per watt of input):
kW = capacity (BTU/h) ÷ (EER × 1000)kWh = kW × run hourscost = kWh × your $/kWh rate
EER already folds in the compressor, fan and everything else the unit draws at rated conditions, so no extra fudge factor is needed. If you only have a seasonal SEER2 number, convert it first (EER ≈ SEER ÷ 0.9, a documented approximation) — SEER is a seasonal average and will slightly understate the peak-hour draw this tool models.
Worked example
A 3-ton central AC (36,000 BTU/h) at EER 12:
- kW = 36,000 ÷ (12 × 1,000) = 3.0 kW
- One hour costs 3.0 kWh × $0.15 = $0.45
- An 8-hour day costs 24 kWh × $0.15 = $3.60
- Over a 120-day cooling season at 8 h/day: 2,880 kWh ≈ $432
Halving the rate to $0.075/kWh halves the cost; a more efficient EER-18 unit of the same capacity draws only 2.0 kW and would run the same hour for $0.30.
How to read the number
A few things this estimate deliberately does not do. It does not model cycling: a right-sized unit runs longer at a steady draw, while an oversized unit short-cycles and can actually cost more for worse comfort, which is why sizing matters (see AC size and the right-sizing guide). It does not add standby or thermostat draw, which are negligible next to the compressor. And it uses the nameplate EER, which is a lab value at rated outdoor conditions — on a 100 °F afternoon the real draw is a little higher.
To budget a whole summer, estimate your daily compressor hours honestly. A thermostat log or a plug-in meter beats guessing. If you want to compare running a heat pump in cooling mode, use the same capacity in the heat-pump running cost tool, and to see whether an efficiency upgrade pays back, try SEER2 upgrade savings.
Reference table
Draw and cost per hour at a sample $0.15/kWh rate (use your own rate in the tool):
| Capacity | kW @ EER 10 | $/h @ EER 10 | kW @ EER 14 | $/h @ EER 14 |
|---|---|---|---|---|
| 1.5 ton | 1.80 kW | $0.27 | 1.29 kW | $0.19 |
| 2 ton | 2.40 kW | $0.36 | 1.71 kW | $0.26 |
| 3 ton | 3.60 kW | $0.54 | 2.57 kW | $0.39 |
| 4 ton | 4.80 kW | $0.72 | 3.43 kW | $0.51 |
| 5 ton | 6.00 kW | $0.90 | 4.29 kW | $0.64 |