Kilojoules to kilocalories (food Calories) (kJ to kcal)

The formula

kcal = kJ × 0.2390057361

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

• 1 kJ = 1000 × J = 1,000 J
• 1 kcal = 1000 × cal = 4,184 J

Dividing the two SI sizes gives the factor: 0.239005736138 (rounded for display; the underlying ratio is fixed by the definitions). The reverse factor is 4.184.

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: 8,368 kJ = 2,000 kcal — 8,368 × 0.2390057361 = 2,000
• A 1 kW heater run for one hour (1 kWh): 3,600 kJ = 860.421 kcal — 3,600 × 0.2390057361 = 860.421
• Lifting 1 kg through 1 m at standard gravity (9.80665 J): 0.00980665 kJ = 0.00234385 kcal — 0.00980665 × 0.2390057361 = 0.00234385
• A visible-light photon (2 eV): 3.20435 × 10⁻²² kJ = 7.65859 × 10⁻²³ kcal — 3.20435 × 10⁻²² × 0.2390057361 = 7.65859 × 10⁻²³

Frequently asked questions