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BTU to Watts Converter

Convert BTU to watts — and to kilowatts, horsepower, calories per second, and foot-pounds per second — with this free BTU to watts converter. Enter any heating or cooling power in BTU per hour and see it in every power unit at once, with exact factors and a worked air-conditioner example.

Common conversions

How it works

A BTU — a British thermal unit — is a unit of heat energy: the energy needed to raise one pound of water by one degree Fahrenheit. But air conditioners, heaters, and boilers are not sold by total energy; they are sold by how fast they can move heat, which is power. That rate is written as BTU per hour (BTU/h), and it is a power unit in exactly the same sense as a watt. A watt is one joule per second, so converting BTU per hour to watts is a matter of converting the energy unit and the time unit together: one BTU is 1,055.06 joules, and one hour is 3,600 seconds, so one BTU per hour equals 1,055.06 ÷ 3,600 = 0.293071 watts.

That single factor unlocks every other power unit. A kilowatt is 1,000 watts, so 12,000 BTU per hour is 3.51685 kilowatts. A mechanical horsepower is defined as 745.699872 watts, which works out to 2,544.43 BTU per hour. A calorie per second is 4.184 watts, and a foot-pound per second is 1.35582 watts. Because all of these are exact definitions, the converter works through watts as its common base: it turns your input into watts first, then divides into whichever unit you asked for, so converting back and forth always returns the number you started with.

To convert BTU per hour to watts, multiply by 0.293071. To go the other way, multiply watts by 3.41214. For example, 12,000 × 0.293071 = 3,516.85 watts, and 1,000 watts × 3.41214 = 3,412.14 BTU per hour. For kilowatts, divide the watt figure by 1,000; for horsepower, divide watts by 745.70. A quick mental shortcut is that 1,000 BTU per hour is about 293 watts, so a 9,000 BTU air conditioner moves heat at roughly 2,640 watts — close enough for a rough check, but use the exact factor when you are sizing equipment.

The number people meet most often is 12,000 BTU per hour, because that is one "ton" of cooling — the cooling power of melting one ton of ice in a day, a definition left over from the days of ice-cooled buildings. A 1-ton air conditioner therefore moves heat at about 3.52 kilowatts. That is cooling capacity, not electricity use: a modern unit with a good efficiency rating may draw only about 1,000 to 1,200 watts of electricity to deliver those 3,517 watts of cooling, because it moves heat rather than making it. Heaters are different — an electric heater turns nearly every watt of electricity into heat, so a 1,500-watt space heater delivers about 5,118 BTU per hour. Keep that distinction in mind when you compare an air conditioner label with your electricity bill.

Worked example

A 1-ton air conditioner is rated at 12,000 BTU per hour. How many watts of cooling power is that, and how many horsepower?

Step 1: Write down the power — 12,000 BTU/h.
Step 2: Use the conversion factor — 1 BTU/h = 0.293071 W.
Step 3: Multiply: 12,000 × 0.293071 = 3,516.85.
Step 4: Read the answer — 3,516.85 watts, or 3.52 kW rounded.
Step 5: For horsepower, divide by 745.70: 3,516.85 ÷ 745.70 = 4.72 HP.

Enter 12,000 in the converter with BTU per hour to watts selected and it gives exactly the same result: 3,516.85 W, with 3.52 kW and 4.72 HP in the table below. As a second check, 1 horsepower converts to 2,544.43 BTU per hour — 745.70 watts × 3.41214 — which is why a 1-HP motor and a 2,544 BTU/h heater are the same power in different units.

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