Watts to Heat Calculator — Power to BTU/h & kcal/h
Convert electrical power (watts) to heat output in any thermal unit — BTU/h, kcal/h, cal/s, J/s, or MJ/h. Includes an efficiency setting for non-ideal heaters; resistive heaters are 100% efficient by default.
W
Output heat unit
%
1,000 W → 3,412.14 BTU/h
- 1
Input power (100% efficiency)
1,000All electrical energy converts to heat in a resistive heater. - 2
Apply conversion factor
1,000 × 3.412141633 = 3,412.14
How does this calculator work?
Multiply watts by 3.412 to get BTU/h, or by 0.860 to get kcal/h. Resistive heaters (electric baseboard, fan heaters) are ~100% efficient. Enter wattage, choose your thermal unit, and optionally adjust efficiency to get the heat output in any unit.
Formula
How this is calculated
In a resistive heater (electric baseboard, toaster, hair dryer), virtually all electrical energy is converted to heat — efficiency is essentially 100%. A 1000 W heater therefore outputs 1000 W of thermal power, equivalent to 3412 BTU/h or 860 kcal/h. The conversion factors follow directly from the definitions: 1 BTU = 1055.06 J, so 1 W = 3600 J/h ÷ 1055.06 J/BTU ≈ 3.412 BTU/h.
If you have a system that is not 100% efficient — for example an old electric furnace rated at 90% — enter 90% and the calculator will apply that fraction to the input watts before converting. Note that heat pumps work differently: their efficiency (COP) exceeds 100%, meaning a 1000 W pump might deliver 3000 W of heat. The efficiency field here models simple fractional losses, not COP-based systems.
BTU/h is the standard unit for HVAC equipment in the US and Canada. One "ton" of air conditioning = 12000 BTU/h ≈ 3517 W. Kilocalories per hour are common in continental Europe and China for heating specifications.
Frequently asked questions
1500 W × 3.412 ≈ 5118 BTU/h (assuming 100% efficiency, which is correct for a simple resistive heater).
All electrical energy that flows into a resistor is dissipated as heat — none is converted to light, sound, or mechanical work (unlike a motor or light bulb). So the thermal output in watts equals the electrical input in watts.
A British Thermal Unit (BTU) is the amount of heat needed to raise 1 pound of water by 1°F. In power terms, BTU/h is how much heat is added per hour. 1 W = 3.412 BTU/h.
Also known as
TG we-Calculate Editorial Team. (2026). Watts to Heat Calculator — Power to BTU/h & kcal/h [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/watts-to-heat-calculator
TG we-Calculate Editorial Team. "Watts to Heat Calculator — Power to BTU/h & kcal/h." TG we-Calculate. 2026. https://we-calculate.com/calculator/watts-to-heat-calculator.
TG we-Calculate Editorial Team, "Watts to Heat Calculator — Power to BTU/h & kcal/h," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/watts-to-heat-calculator
@misc{wecalculate_watts_to_heat_calculator, title = {Watts to Heat Calculator — Power to BTU/h & kcal/h}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/watts-to-heat-calculator}}, year = {2026}, note = {TG we-Calculate} }
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