What is being measured?
Energy is a quantity that can be transferred as work or heat. A unit conversion does not determine which physical process produced it.
Calories are thermochemical. BTU uses the international-table definition. Foot-pounds mean foot-pounds force.
Meaning of ft·lbf
foot pounds uses the symbol ft·lbf in this library and measures energy. Under the stated reference convention, 1 ft·lbf = approximately 1.35581794833 J. This equivalence changes how a known value is written. It does not increase measurement accuracy or establish whether a measurement is appropriate to a real application.
Conversion method
Multiply the value by the source factor (1.3558179483314004), then divide by the target factor (1). The factor ratio expresses the same energy measurement in the other unit.
Worked example
For a known value of 10 ft·lbf, the reference conversion gives 13.5581794833 J. Converting that result back gives approximately 10 ft·lbf. This reverse check helps catch a reversed factor, but matching round-trip arithmetic alone does not independently verify a source definition.
Common reference values
| Input (ft·lbf) | Reference equivalent (J) |
|---|---|
| 1 | 1.35581794833 |
| 5 | 6.77908974166 |
| 10 | 13.5581794833 |
| 25 | 33.8954487083 |
| 50 | 67.7908974166 |
| 100 | 135.581794833 |
Compare one ft·lbf with other units
| Target unit | Equivalent of 1 ft·lbf | Definition guide |
|---|---|---|
| Joules (J) | 1.35581794833 | Read definition |
| Kilojoules (kJ) | 0.00135581794833 | Read definition |
| Kilowatt-hours (kWh) | 3.76616096759e-7 | Read definition |
| Thermochemical calories (cal) | 0.32404826681 | Read definition |
| International-table BTU (BTU IT) | 0.00128506746346 | Read definition |
| electronvolts (eV) | 8462350027830000000 | Read definition |
| kilocalories (kcal th) | 0.00032404826681 | Read definition |
| megajoules (MJ) | 0.00000135581794833 | Read definition |
Precision and common mistakes
- Keep the source and target quantity consistent. A matching symbol is not enough to establish a compatible definition.
- Record the original measurement precision. Showing twelve significant digits in a table does not make a rounded input more precise.
- Check symbol capitalization, prefixes and any regional convention in the source. Use the displayed unit definition rather than a similarly named unit.
- Factors involving repeating fractions or π use finite numerical precision. Round the final answer to the precision justified by your input.
Use a working converter
- Energy converter
- Foot pounds to Joules converter
- Foot pounds to Kilojoules converter
- Foot pounds to megajoules converter
- Foot pounds to watt hours converter
- Foot pounds to Kilowatt-hours converter
Source and verification scope
Examples and tables are computed from the versioned unit definitions used by the linked converters. The source access dates appear below. Computandum is independent of the cited organizations; a citation does not mean that a publisher endorses this page or an actual project.
Sources
- NIST / BIPM: NIST: unit conversion factors ↗ · 2026-10-08