Kilojoule to Joule
Free instant kilojoule to joule converter. 1 kJ = 1000 J.
Common Kilojoule to Joule values
| Kilojoule (kJ) | Joule (J) |
|---|---|
| 1 | 1000 |
| 5 | 5000 |
| 10 | 10000 |
| 25 | 25000 |
| 50 | 50000 |
| 100 | 100000 |
| 500 | 500000 |
| 1000 | 1000000 |
How does Kilojoule to Joule conversion work?
Type a value in the Kilojoule (kJ) field and the equivalent in Joule (J) appears instantly to the right. The math uses the exact formula shown above — no rounding errors, no approximations beyond standard floating-point precision. Use the swap button to flip the units and see the inverse conversion.
Kilojoule. 1,000 joules. Common unit on food labels in metric countries.
Joule. The SI unit of energy. About the energy of a small apple falling from waist height.
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Conversion factors come from the official standard (NIST, BIPM, ISO definitions where applicable). Values are precise to standard floating-point limits.
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How it works — the formula
1 cal (thermochemical) = 4.184 J exactly
1 kcal = 4,184 J = 4.184 kJ
1 kWh = 3,600,000 J = 3.6 MJ
1 BTU (IT) = 1,055.05585262 JThe joule is the SI derived unit of energy: 1 J = 1 N·m = 1 W·s. The "calorie" exists in three flavors — thermochemical (4.184 J exact, used in chemistry), International Table (4.1868 J, used in nutrition tables in some countries), and 15 °C (~4.1855 J). US food labels and the FDA use the thermochemical kilocalorie. The BTU is defined as the energy needed to raise 1 lb of water by 1 °F; the International Table BTU (1,055.05585262 J) is the standard for HVAC and energy markets per ISO 31.
Worked examples
- Inputs:
- 500 kcal = ? J
- Output:
- 500 × 4,184 = 2,092,000 J = 2.092 MJ
- Inputs:
- 1 kWh = ? BTU
- Output:
- 3,600,000 / 1,055.05585262 ≈ 3,412.14 BTU
- Inputs:
- 10,000 BTU/h cooling
- Output:
- 10,000 × 1,055.05585262 / 3,600 ≈ 2,930.7 W ≈ 2.93 kW
Limitations
- "Calorie" without a qualifier is ambiguous — nutrition labels almost always mean kilocalories (1 Calorie = 1 kcal = 1,000 cal).
- BTU comes in five definitions (IT, thermochemical, 39 °F, 59 °F, 60 °F) within ~0.1% — the IT BTU is the most common modern usage.
- Electronvolt (1 eV ≈ 1.602 × 10⁻¹⁹ J) is standard in atomic physics but not used for everyday energy.
- Energy and power are different units (energy = power × time); 1 watt ≠ 1 joule, and 1 kWh ≠ 1 kW.
Conversions are exact for joule-defined units (calorie, kWh, BTU-IT). Food-calorie counts on labels are reported with two-significant-digit precision and may differ from thermochemical equivalents at the third digit.