Convert Watt-Hour to British Thermal Unit (Wh → BTU)

Converting watt-hours to BTU is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in watt-hours

   Start with the number of watt-hours (Wh) you want to convert.
2. 2
   Multiply by 3.412142

   The conversion factor from Wh to BTU is 3.412142. Multiply your value by this number.
3. 3
   Read the result in BTU

   The result is your value in BTU (BTU).

Multiply the value in watt-hours by 3.412142. For the reverse direction, multiply by 0.293071.

• ✓1 Wh = 3600 J = 0.001 kWh.
• ✓Battery mAh × V = Wh. A 3000 mAh phone battery at 3.7 V = 11.1 Wh.
• ✓Airline limits lithium batteries to 100 Wh for carry-on.

• ✗Confusing mAh with Wh — need voltage to convert.
• ✗Using Wh when kWh is more appropriate for large batteries.
• ✗Forgetting the voltage in battery capacity calculations.

What is the Watt-Hour?

The watt-hour equals exactly 3,600 joules and is the standard unit for small-battery capacity, household electrical energy, and renewable-energy storage. A smartphone battery stores roughly 12–15 Wh, a laptop battery 50–100 Wh, and an electric car battery 60,000–100,000 Wh (60–100 kWh). The watt-hour represents the energy delivered by a 1-watt device running for 1 hour. It is the natural unit for connecting power (watts) to time, which is why electric utilities bill in kilowatt-hours. The watt-hour relates to the joule (3,600 J = 1 Wh), the kilowatt-hour (1,000 Wh = 1 kWh), and the BTU (1 Wh ≈ 3.412 BTU). Battery capacity, solar panel output (Wh per day), and energy storage system specifications all rely on the watt-hour as the base small-energy unit.

• Laptop and phone battery capacity
• Portable power banks and UPS
• Home solar panel daily output

What is the British Thermal Unit?

The British thermal unit (BTU) equals approximately 1,055.06 joules and is the standard unit in American HVAC, gas appliances, and air-conditioner ratings. Originally defined as the heat needed to raise 1 pound of water by 1°F, the BTU is the imperial counterpart to the calorie. American gas utilities measure delivered heat in BTUs or therms (1 therm = 100,000 BTU), and air conditioners are rated by their cooling capacity in BTU per hour (a typical window AC is 5,000–12,000 BTU/h, central AC for a medium home is 24,000–60,000 BTU/h). Furnaces are similarly rated. The BTU relates to the joule (1 BTU ≈ 1,055 J), the calorie (1 BTU ≈ 252 cal), the watt-hour (1 BTU ≈ 0.293 Wh), and the therm (100,000 BTU = 1 therm). Outside the United States, the BTU is rare; metric countries use kilojoules or kilowatt-hours for the same applications.

• US air-conditioner sizing
• US heating-system capacity
• Natural gas billing in some US regions