Methods: Energy unit converter
calc.energy-units.convert · Version 0.2.0
Method
Convert the amount to joules with its unit's definition, then from joules to the target unit. Fuels use EIA's published average heat content in Btu.
Assumptions
- Btu means the International Table Btu, 1,055.05585262 joules.
- A therm is 100,000 Btu (International Table), as EIA defines it. NIST SP 811 calls this the therm (EC); its therm (U.S.) is about 0.024% smaller.
- Fuel heat contents are US averages for the year shown, not the content of any one delivery.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units, 2008, Appendix B.8, British thermal unit (IT) and kilowatt hour to joule
- EIA, Heat Content of Natural Gas Consumed, Annual, 2025, US, delivered to consumers, Btu per cubic foot
- EIA, Monthly Energy Review, Appendix A, Table A1, approximate heat content of petroleum products
- EIA, Energy conversion calculators, 2026 estimates, Coal, electric power sector, Btu per short ton
- EIA, British thermal units (Btu), Energy Explained, Therm and MMBtu definitions
Worked examples
| Example | Independent source | Tolerance | Last result |
|---|---|---|---|
| 12 MWh to MMBtu | calc/energy-units-and-emissions spec, scenario "MWh to MMBtu"; factor from the NIST SP 811 Btu (IT) definition | ±0.0001 | Passed on Oct 31, 2026 |
| 1,000 cubic feet of natural gas to Btu | EIA 2025 US average of 1,036 Btu per cubic foot | ±0.001 | Passed on Oct 31, 2026 |
| 1 kWh to Btu | NIST SI derivation: 3.6 MJ ÷ 1,055.05585262 J per Btu | ±0.005 | Passed on Oct 31, 2026 |
| 1 therm to kWh | 100,000 Btu (EIA) × 1,055.05585262 J (NIST) ÷ 3.6 MJ | ±0.0001 | Passed on Oct 31, 2026 |
| 1 short ton of coal to MMBtu | EIA 2026 estimate, electric power sector | ±0.0001 | Passed on Oct 31, 2026 |
Known differences from reference engines
None recorded.
Cite this tool
Energy unit converter, version 0.2.0. gridprims. https://gridprims.com/tools/calc/energy-units/convert/