Watts to BTU per Hour Converter (W to BTU/h)

Almost every watt an electric device draws ends up as heat in the room, whether it comes from a space heater, a light fixture, a computer or a refrigerator's compressor. HVAC load calculations in the US add up those gains in BTU per hour, so converting wattage to BTU/h is the usual first step when sizing cooling for an office, a server closet or a home theater.

The factor is about 3.412 BTU/h per watt. A 1,500 W portable heater, the usual top setting on US plug-in heaters, gives out about 5,118 BTU/h whatever its style, because resistance heaters all turn their full input into heat; a fan model simply spreads that heat around the room faster.

How to use this tool

1. Type a value in the Watt box to see it in British thermal units per hour, or type in the British Thermal Unit per Hour box to convert the other way.
2. Press ⇄ to swap the two units, or Load example for a typical value.
3. Check the charts below for common values; for other units, open the Power converter.

Formula

British Thermal Unit per Hour (BTU/h) = Watt (W) × 3.41214163313

Watt (W) = British Thermal Unit per Hour (BTU/h) × 0.293071070172

Both factors come from exact definitions: 1 british thermal unit per hour = 0.293071070172 watts and 1 watt = 3.41214163313 British thermal units per hour (shown to 12 significant digits).

Example

Two conversions worked with the same factors the converter uses:

1500 W × 3.41214163313 ≈ 5118.21 BTU/h

10000 BTU/h × 0.293071070172 ≈ 2930.71 W

Watt to British Thermal Unit per Hour chart

Common values from watts to British thermal units per hour, rounded to four decimal places.

British Thermal Unit per Hour to Watt chart

The reverse direction for values people often look up.

Heat sources measured in watts

Quick mental estimate

Multiply by 3.4: 1,500 W → 5,100 BTU/h. That is about 0.35% under the exact 3.41214, small next to the safety margin used when sizing air conditioning.

Use the converter or the charts when the exact figure matters.

The two units

Watt (W): The watt (W) is the SI unit of power, one joule of energy per second. Light bulbs, appliances, chargers and electronics are rated in watts.

British Thermal Unit per Hour (BTU/h): One International Table BTU per hour (BTU/h) is about 0.293071 W. In this power converter the shorthand BTU means BTU/h, as in cooling-capacity ratings; a quantity of BTU energy alone cannot be converted to watts without a time interval.