Result
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Units and SI factors
All units are referenced to the SI base J (Joule).
| Unit | Name | Factor to SI | 1 unit = ? SI |
|---|
Energy in engineering practice
Energy is the capacity to do work, and its SI unit is the joule (J) — one newton applied over one metre. Practical systems scale this to kilojoules (kJ) and megajoules (MJ), while electricity billing uses the kilowatt-hour (kWh). In US thermal practice the British thermal unit (BTU) dominates, food and chemistry use the calorie (cal) and kilocalorie (kcal), and imperial mechanics often quote foot-pound force (ft·lbf).
Where each unit shows up
- J / kJ / MJ — physics, mechanical work and fuel energy content.
- kWh — electricity meters and battery capacity.
- BTU — heating, cooling and gas appliances in the US.
- cal / kcal — food nutrition and chemical calorimetry.
- ft·lbf — imperial mechanical work and airgun muzzle energy.
Conversion gotchas
“Calorie” is notoriously ambiguous: the small cal is 4.184 J, while the food Calorie (capital C, or kcal) is 1000× that. The BTU also has several definitions — this site uses the common IT value of 1055.06 J. Exact anchor: 1 kWh = 3.6 MJ = 3 600 000 J.
Method: every unit has a factor that maps it to its SI base. We compute value × source factor ÷ target factor, so round-trips agree to better than 1e-9.