BTU to kW: How to Convert Cooling Power for Cost Estimates
One BTU/hr is 0.00029307107 kW. One kW is 3,412.14163 BTU/hr. This reference shows how to convert your air conditioner's nameplate rating and — more usefully — how to estimate its running cost from its power draw, not its capacity.
What BTU/hr actually measures
BTU/hr is a rate of heat transfer, not power consumption. An air conditioner rated 12,000 BTU/hr moves that much heat out of your room per hour at rated conditions. It tells you how big a space the unit can cool — not how much electricity it draws. That distinction is exactly where most cost estimates go wrong.
The conversion factor
Because BTU/hr is an imperial heat-flow unit and kW is a metric power unit, they convert through a fixed physical factor:
BTU/hr = kW × 3,412.14163
12,000 BTU/hr ÷ 3,412.14163 = 3.52 kW
This is a unit conversion — the answer is exact by definition. The factor comes from the NIST definition of the Btu and the watt (0.29307107 W per Btu/hr).
Wait — 12,000 BTU/hr is only 3.5 kW? That seems low.
It's correct, and it's the whole point. A 1.5 ton (18,000 BTU/hr) unit is 5.28 kW of cooling power, but it consumes nowhere near 5 kW of electricity. The difference is the efficiency ratio below.
Why you need EER (or a nameplate) for cost
An air conditioner with 12,000 BTU/hr of capacity and an EER of 12 draws:
12,000 ÷ 12 = 1.0 kW
So the unit consumes ~1 kW while delivering 3.5 kW of cooling. Using the capacity figure (3.52 kW) as if it were consumption would overstate your bill by roughly 3.5×.
The most reliable number is still the nameplate's "input power" or "power consumption" in watts — divide by 1,000 and you have kW directly. EER on the label gets you the same thing from capacity.
From kW to running cost
Once you have input power in kW, the cost estimate is two multiplications:
- Energy (kWh) = input power (kW) × running hours
- Cost = energy × your rate (price per kWh)
Worked example — an 18,000 BTU/hr unit with EER 10 (1.8 kW input) running 6 hours a day at $0.15/kWh:
10.8 × $0.15 = $1.62/day
Need the arithmetic done for you? The AC Running Cost Calculator accepts direct kW or BTU/hr and EER, then returns daily, monthly and yearly estimates.
Common conversion mistakes
- Treating capacity as consumption. The #1 error — always divide by EER or read input power.
- Confusing BTU/hr with BTU. Ratings are per hour. For billing you want energy in kWh — BTU/hr × hours ÷ 3,412.14163.
- Mixing ton and kW. One "ton" of cooling = 12,000 BTU/hr = 3.52 kW capacity.
- Rounding to 3.41 too early. Fine for quick numbers; the difference adds up over a season.
How this guide was checked
The conversion factor in this article matches the NIST-based definition used by the AC Running Cost Calculator (3412.14163). Worked examples were re-derived, not copied. Corrections are welcome at info@dailyutilitylab.com; see our editorial policy.
Sources
- National Institute of Standards and Technology — Guide for the Use of the International System of Units (SI), Table 6 (conversion factors)
- U.S. Energy Information Administration — Electricity use in homes
- U.S. Department of Energy — Estimating appliance and home electronic energy use