Foot-pounds to joules (ft·lbf to J)

The formula

J = ft·lbf × 1.355817948

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

• 1 ft·lbf = ft × lbf = 1.35581794833 J
• 1 J is the SI unit of energy.

Dividing the two SI sizes gives the factor: 1.35581794833 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 0.737562149277.

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): 6,171,920 ft·lbf = 8,368,000 J — 6,171,920 × 1.355817948 = 8,368,000
• A 1 kW heater run for one hour (1 kWh): 2,655,220 ft·lbf = 3,600,000 J — 2,655,220 × 1.355817948 = 3,600,000
• Lifting 1 kg through 1 m at standard gravity: 7.23301 ft·lbf = 9.80665 J — 7.23301 × 1.355817948 = 9.80665
• A visible-light photon (2 eV): 2.36341 × 10⁻¹⁹ ft·lbf = 3.20435 × 10⁻¹⁹ J — 2.36341 × 10⁻¹⁹ × 1.355817948 = 3.20435 × 10⁻¹⁹

Frequently asked questions