BTU to kW Calculator
Convert cooling and heating capacity between BTU/hr, kilowatts, tons and watts — the numbers you need to size an AC and the solar to run it.
1 ton of cooling = 12,000 BTU/hr = 3.517 kW. This is thermal (cooling/heating) capacity, not the electricity the unit draws — divide by the system COP/EER for input power.
How this conversion works
1 BTU/hr = 0.29307 W, 1 kW = 1000 W, 1 ton = 3516.85 W = 12,000 BTU/hr, 1 kcal/hr = 1.163 W.To get the electrical draw of an AC or heat pump, divide the cooling capacity by its efficiency (EER or COP).
Capacity units for AC and heat pumps
Air conditioners and heat pumps are rated by how much heat they move per hour — in BTU/hr (US), kW (metric) or tons (1 ton = 12,000 BTU/hr). These describe cooling or heating capacity, not the electricity consumed. A unit’s electrical draw is the capacity divided by its efficiency, so a 3.5 kW (1 ton) unit with a COP of 3.5 draws only about 1 kW of power.
From capacity to solar
Once you know the electrical draw, the mini-split calculator and load calculator turn it into panels and battery. A common 1.5 ton (18,000 BTU) AC is about 5.3 kW of cooling, typically drawing 1.5–1.8 kW electrically.
Standard AC sizes, converted
| Marketed size | BTU/hr | Cooling kW | Typical electrical draw* |
|---|---|---|---|
| 0.75 ton | 9,000 | 2.6 | 0.7–0.9 kW |
| 1 ton | 12,000 | 3.5 | 0.9–1.2 kW |
| 1.5 ton | 18,000 | 5.3 | 1.3–1.8 kW |
| 2 ton | 24,000 | 7.0 | 1.8–2.4 kW |
| 3 ton | 36,000 | 10.6 | 2.7–3.6 kW |
*Electrical draw assumes a modern inverter unit (COP ~3); older fixed-speed units sit at the top of each range or above. This distinction — thermal capacity vs electrical input — is the most common source of AC-sizing confusion.
Frequently asked questions
12,000 BTU/hr equals about 3.52 kW of cooling capacity, which is one ton of refrigeration.
No. BTU/hr and kW here measure cooling capacity, not electricity drawn. Divide capacity by the unit efficiency (EER or COP) to get electrical power.
24,000 BTU/hr is 2 tons of cooling, roughly 7 kW of capacity.
Find the electrical draw (capacity divided by COP/EER), then use the load and mini-split calculators to size the panels and battery for the hours it runs.
Sources & standards
These capacity conversions follow the same thermal-unit definitions and efficiency ratings HVAC manufacturers and standards bodies use to rate cooling and heating equipment.
- ASHRAE Terminology — "Ton of Refrigeration" — ASHRAE
Authoritative definition of the ton-of-refrigeration unit this calculator converts to and from. - NIST Special Publication 811 — Guide for the Use of the International System of Units (SI) — National Institute of Standards and Technology
Governing conversion factors between BTU, watts and kilowatts used throughout this tool. - AHRI Standard 210/240 — Performance Rating of Unitary Air-Conditioning & Air-Source Heat Pump Equipment — Air-Conditioning, Heating, and Refrigeration Institute
Defines how EER/SEER and COP ratings are measured, the figures used to go from cooling capacity to electrical draw. - ENERGY STAR — Central Air Conditioners and Air Source Heat Pumps — U.S. EPA / U.S. Department of Energy
Reference for the typical modern-equipment COP/EER values used in this calculator's electrical-draw estimate.