British thermal units (IT) to joules (BTU to J)

The formula

J = BTU × 1,055.05585262

Where the factor comes from — each unit by its definition, then its size in SI:

• 1 BTU = 1055.05585262 × J = 1,055.05585262 J
• 1 J is the SI unit of energy.

Dividing the two SI sizes gives the factor: 1,055.05585262, exact — every step above is a definition, not a measurement. The reverse factor is 0.000947817120313.

The SI unit of energy is the joule. Food labels use kilocalories, electricity bills kilowatt-hours, heating specs BTU and particle physics electronvolts — the same quantity in five costumes.

Worked examples

• A day's food (2000 kcal): 7,931.33 BTU = 8,368,000 J — 7,931.33 × 1,055.055853 = 8,368,000
• A 1 kW heater run for one hour (1 kWh): 3,412.14 BTU = 3,600,000 J — 3,412.14 × 1,055.055853 = 3,600,000
• Lifting 1 kg through 1 m at standard gravity: 0.00929491 BTU = 9.80665 J — 0.00929491 × 1,055.055853 = 9.80665
• A visible-light photon (2 eV): 3.03714 × 10⁻²² BTU = 3.20435 × 10⁻¹⁹ J — 3.03714 × 10⁻²² × 1,055.055853 = 3.20435 × 10⁻¹⁹

Frequently asked questions