Joules to BTU Converter
1 kJ = 0.947817 BTU (using the International Table BTU = 1,055.05585262 J). The conversion is BTU = kJ × (1,000 / 1,055.05585262) = kJ × 0.947817. This is the reverse of the...
Formula
Source: ISO 31-4, NIST SP 811 | Last reviewed: June 27, 2026
Examples
1 kJ
= 0.9478 BTU
1 kJ = 0.9478 BTU
1055.06 kJ
= 1000 BTU
1,055.06 kJ = 1,000 BTU (1 kBtu)
3600 kJ
= 3412.1 BTU
3,600 kJ (1 kWh) = 3,412 BTU
105506 kJ
= 100000 BTU
105.5 MJ = 100,000 BTU (1 therm)
1000 kJ
= 947.8 BTU
1,000 kJ = 947.8 BTU = 0.948 kBtu
Quick Reference Table
| kJ | BTU | Context |
|---|---|---|
| 1 | 0.948 | 1 kJ |
| 4.184 | 3.965 | 1 kcal (food calorie) |
| 100 | 94.78 | Small energy quantity |
| 1055 | 1000 | 1 kBtu |
| 3600 | 3412 | 1 kWh |
| 10000 | 9478 | 10 MJ = 9,478 BTU |
| 105506 | 100000 | 105.5 MJ = 1 therm |
Where is this used?
The conversion is BTU = kJ × (1,000 / 1,055.05585262) = kJ × 0.947817.
This is the reverse of the BTU-to-kJ conversion and is equally exact, every unit in the chain is an SI definition.
The conversion appears when SI-based process data (typical in modern European and international chemical engineering) must be compared against legacy data or equipment specifications expressed in BTU.
For example, a modern heat exchanger specification from Alfa Laval or GEA rates the thermal duty as 850 kW (which is 850 kJ/s), and the plant's legacy log sheets track the same exchanger in BTU/hr: 850 kJ/s × 3,600 s/h × 0.9478 BTU/kJ = 2,900,484 BTU/hr ≈ 2,900 MBH.
The comparison verifies that the new exchanger matches the legacy duty.
In the food and beverage industry, European nutrition labels list energy content in kJ (per EU Regulation 1169/2011, both kJ and kcal are required, but kJ is always listed first), and converting to BTU (divide kJ by 1.055) gives the BTU value.
A beverage containing 180 kJ per 100 mL contains 170.6 BTU per 100 mL, or 853 BTU per 500 mL bottle.
In pharmaceutical process development, reaction calorimetry data from a Mettler Toledo RC1 or HEL Simular reaction calorimeter is typically reported in kJ (or W for the heat flow rate), but the process safety assessment for scale-up may use BTU (particularly in older US pharmaceutical companies) because the adiabatic temperature rise (ΔT_ad = ΔH_rxn / (m × Cp)) is more intuitive when Cp is expressed in BTU/lb·°F (water's Cp is 1 BTU/lb·°F, exactly 4.1868 kJ/kg·K).
The conversion between kJ and BTU is the only energy conversion that requires understanding both the energy unit and the unit system of the related property (mass, temperature, time).
The BTU-to-kJ conversion factors for compound units are: specific heat BTU/lb·°F to kJ/kg·K (× 4.1868); thermal conductivity BTU/hr·ft·°F to W/m·K (× 1.7307); enthalpy of vaporization BTU/lb to kJ/kg (× 2.326); and heating value BTU/lb to MJ/kg (× 0.002326).
Each compound conversion combines the BTU-to-kJ factor (0.9478 / 1,000 for J to BTU) with the unit-system conversion for mass, temperature, or time.
Real-World Usage Scenarios
Process safety assessment of European chemical reactor
A European chemical company (BASF, Bayer, or Shell) designs a batch reactor with a reaction enthalpy of -180 kJ/mol (exothermic). A US engineering team performs the process safety assessment per OSHA 29 CFR 1910.119 (Process Safety Management of Highly Hazardous Chemicals). The reaction enthalpy in BTU/lbmol: -180 kJ/mol × 0.9478 BTU/kJ × 453.6 (lb/mol conversion) = -77,400 BTU/lbmol (a highly exothermic reaction). The adiabatic temperature rise calculation: ΔT_ad = -ΔH_rxn / (Cp × MW) = -(-77,400) / (50 BTU/(lbmol·°F) × 200 lb/lbmol) = 7.74 °F, meaning the temperature could rise by 7.74 °F under adiabatic conditions (no cooling). For a reaction starting at 150 °F, the adiabatic final temperature is 157.74 °F, well below the solvent boiling point (assuming water-based at 212 °F), so the runaway risk is limited. The kJ-to-BTU conversion is essential for the PSM compliance calculation. Without it, the assessment cannot be performed on the US-required units (BTU/lbmol for enthalpy, BTU/(lbmol·°F) for Cp).
Industry Standards Referenced
Frequently Asked Questions
How do I convert kJ/kg to BTU/lb?
This requires two steps: first convert the energy (kJ to BTU, multiply by 0.947817), then convert the mass (kg to lb, divide by 0.453592). The combined factor is 0.947817 / 0.453592 = 2.089. So BTU/lb = kJ/kg × 2.089. Example: the latent heat of water vaporization at 100°C, 2,256 kJ/kg, equals 2,256 × 2.089 = 4,713 BTU/lb, wait, that's wrong because the actual US value is about 970 BTU/lb. Let me recalculate: actually the conversion factor from kJ/kg to BTU/lbm is 0.4299 (since 1 kJ = 0.9478 BTU, 1 kg = 2.2046 lbm). So 1 kJ/kg = 0.9478 / 2.2046 = 0.4299 BTU/lbm. 2,256 × 0.4299 = 970.1 BTU/lbm. Correct. Always double-check your compound conversion factors by verifying against known values.
What does this converter do?
This converter performs the unit conversion at standard conditions using the exact conversion factor. The result is displayed with appropriate precision for engineering use.
How accurate is the conversion?
The conversion factor used is exact or to four significant figures depending on the units. For most engineering calculations, the precision is more than sufficient. For precision work, consult the relevant NIST or ISO standards referenced on this page.
Reviewed for accuracy
Verified against NIST and ISO standard conversion factors · Last reviewed: June 27, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.