Power conversion starts with the watt
The watt is the SI coherent unit of power, equal to one joule per second. CalcOS converts each supported power unit through watts and rounds only the displayed result.
result = value × source-to-W ÷ destination-to-W
Power is a rate. Converting power to energy requires a duration, so joules and kilowatt-hours remain in the Energy Converter.
Horsepower and rate variants
| Unit | Watt relationship | Status |
|---|---|---|
| mechanical horsepower | 745.6998715822702 W | exact derived |
| metric horsepower | 735.49875 W | exact |
| electrical horsepower | 746 W | exact convention |
| boiler horsepower | ≈ 9,809.50 W | NIST published factor |
| BtuIT per hour | ≈ 0.2930711 W | NIST published factor |
| Btuₜₕ per hour | ≈ 0.2928751 W | NIST published factor |
There is no safe unlabeled horsepower
“Horsepower” can describe several different units. CalcOS labels mechanical, metric, electrical, and boiler horsepower separately. The focused hp↔kW pages state that they use mechanical horsepower.
Power is not energy
A kilowatt describes a rate; a kilowatt-hour describes energy accumulated while that rate persists over time. They cannot be converted without a duration.
Popular power converters
Authoritative references: BIPM SI Brochure and NIST SP 811 Appendix B.9.