About the BTU to Watts Converter
This BTU to watts converter translates heating and cooling capacity between BTU per hour (BTU/h), the unit on most US air conditioners, furnaces and space heaters, and watts or kilowatts, the unit used for electric appliances and in most other countries. It also shows tons of refrigeration and horsepower, and converts in any direction.
Use it to compare a 12,000 BTU mini-split with a 3.5 kW heat pump, to size an electric heater against a gas one, to check whether a portable AC is powerful enough for a room, or to read European product sheets. Remember that an air conditioner’s BTU rating is its cooling output, not the electricity it draws — divide by the unit’s efficiency (EER or COP) to estimate electrical watts.
The calculator uses the International Table BTU (1,055.05585262 joules), so 1 BTU/h = 0.29307 W and 1 W = 3.41214 BTU/h.
With the default inputs, the converted power is 3,516.853. Change any value above to recalculate instantly.
How to use the btu to watts converter
- 1Enter the rating from the appliance label or spec sheet.
- 2Choose the unit it is in — usually BTU/h for AC units or W/kW for electric heaters.
- 3Choose the unit you want to compare against.
- 4Read the converted value and check the chart against common AC sizes.
Formula and method
A BTU (British thermal unit) is an amount of energy — 1,055.05585262 joules on the International Table definition — and a watt is one joule per second. So one BTU per hour is 1,055.056 ÷ 3,600 = 0.29307 watts, and one watt is about 3.412 BTU/h. Kilowatts are watts ÷ 1,000.
A ton of refrigeration is the cooling capacity of 12,000 BTU/h (3.517 kW), historically the rate at which a ton of ice melts in 24 hours. Mechanical horsepower is 745.7 W. The energy-per-hour output is simply kW × 1 h, the heat moved in one hour of running at full capacity.
- BTU/h
- British thermal units per hour (heating/cooling rate)
- W
- Watts (joules per second)
- ton
- Ton of refrigeration = 12,000 BTU/h
Worked examples
12,000 BTU/h mini-split to watts
12,000 × 0.29307 = 3,516.85 W, or 3.52 kW of cooling — exactly one ton of refrigeration.
1,500 W space heater to BTU/h
1,500 × 3.41214 = 5,118 BTU/h. A plug-in electric heater turns essentially all its electricity into heat.
5,000 BTU window AC in kW
5,000 × 0.29307 ÷ 1,000 = 1.47 kW of cooling capacity.
3-ton central AC to kW
3 tons × 12,000 = 36,000 BTU/h, which is 36,000 × 0.29307 = 10.55 kW.
Frequently asked questions
How many watts is 1 BTU?+
A BTU is energy and a watt is power, so the useful comparison is per hour: 1 BTU/h = 0.29307 W. One BTU of energy equals 0.000293 kWh (1,055 joules).
How many watts does a 12,000 BTU air conditioner use?+
12,000 BTU/h of cooling equals 3,517 W of heat removed, but the electricity used is lower — typically around 1,000–1,200 W for an efficient unit with an EER of 10–12.
How do I convert watts to BTU?+
Multiply watts by 3.412 to get BTU per hour. A 2,000 W heater produces about 6,824 BTU/h.
What is a ton in air conditioning?+
A ton of refrigeration is 12,000 BTU/h, about 3.52 kW of cooling. A 2.5-ton central air system therefore moves 30,000 BTU/h.
How many BTU do I need to heat or cool a room?+
A common rule of thumb is about 20 BTU/h per square foot for cooling in a typical climate, adjusted for sun, ceiling height, insulation and occupants. A professional load calculation gives the most accurate size.