The formula
BTU/h = W × 3.412141633
Where the factor comes from — each unit by its definition, then its size in SI:
1 W is the SI unit of power.1 BTU/h = BTU / h = 0.293071070172 W
Dividing the two SI sizes gives the factor: 3.41214163313 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 0.293071070172.
Power is energy per second; the watt is one joule per second. Engine ratings in horsepower and air-conditioner ratings in BTU/h convert to watts with fixed factors.
Worked examples
- A small car engine (100 hp): 74,570 W = 254,443 BTU/h — 74,570 × 3.412141633 = 254,443
- An old incandescent bulb: 60 W = 204.728 BTU/h — 60 × 3.412141633 = 204.728
- An electric kettle (2 kW): 2,000 W = 6,824.28 BTU/h — 2,000 × 3.412141633 = 6,824.28
- A room air conditioner: 3,516.85 W = 12,000 BTU/h — 3,516.85 × 3.412141633 = 12,000
Frequently asked questions
How many BTU per hour is 1 W?
1 W = 3.41214163313 BTU/h.
How do I convert BTU per hour back to watts?
Divide by 3.41214163313 — or multiply by 0.293071070172: 1 BTU/h = 0.293071070172 W.