About Power Unit Converter — kW, HP, BTU/h & Tons of Refrigeration
The power unit converter translates between the units that motors, engines, and HVAC equipment mix on every project: watts and kilowatts from SI documentation, horsepower from US motor nameplates, PS (metric horsepower) from European and Japanese engine ratings, BTU/h from US heating and cooling equipment, tons of refrigeration from air-conditioning capacity, and kcal/h from older metric heating literature. Every conversion runs through the watt using NIST SP 811 Appendix B factors.
The trap this tool refuses to blur: there are two horsepowers. Mechanical horsepower — 550 ft·lbf/s = 745.6999 W — is what US motor nameplates mean; metric horsepower (PS, cavallo, cheval) — 735.4988 W — is what European engine brochures mean. They differ by 1.4%, enough to matter in a compliance calculation, so the converter lists them as separate units. The other anchors: 1 kW ≈ 1.341 hp ≈ 3,412 BTU/h, and 1 ton of refrigeration = 12,000 BTU/h ≈ 3.517 kW.
How It Works
- Enter the power value, pick the unit it is currently in ("from"), and pick the unit you need ("to"). The headline shows the converted value; the table beneath shows the same power in all eight units at once.
- Every conversion is value × (watts per from-unit) ÷ (watts per to-unit). The SI ladder is exact; hp, PS, BTU/h, and tons carry the published NIST 7-significant-figure values; kcal/h is exact (4,186.8 J per kcal IT ÷ 3,600 s = 1.163 W).
- Displayed values are rounded to 6 significant digits; the conversion itself runs in full double precision, so converting back returns your original number.
- Remember that power converts, ratings do not: a motor's output rating, an engine's SAE-vs-DIN test basis, and a boiler's input-vs-output all involve efficiency and test-condition questions on top of the unit arithmetic. This tool does the arithmetic exactly; the rating basis is yours to check.
Worked Example
A 10 hp US motor nameplate needs a kW figure for a European schedule. Through the watt: 10 hp × 745.6999 W/hp = 7,456.999 W = 7.456999 kW — call it 7.46 kW. Had the source been a 10 PS engine brochure, the answer would be 7.354988 kW, 1.4% lower — the two-horsepowers trap the tool keeps explicit. As a cross-check, the chart's "10 kW" row reads 13.4102 hp, and 10 kW ≈ 34,121 BTU/h ≈ 2.84 tons of cooling.
kW to HP conversion chart (with PS and BTU/h)
Common kilowatt ratings converted with the NIST SP 811 factors (1 hp = 745.6999 W mechanical; 1 PS = 735.4988 W metric), shown to 6 significant digits — exactly what the converter outputs for the same inputs.
| Power | hp (mech.) | PS (metric) | BTU/h |
|---|---|---|---|
| 1 kW (space heater) | 1.34102 | 1.35962 | 3,412.14 |
| 5 kW (EV charger) | 6.70511 | 6.79811 | 17,060.7 |
| 10 kW (small motor) | 13.4102 | 13.5962 | 34,121.4 |
| 50 kW (fast charger) | 67.0511 | 67.9811 | 170,607 |
| 100 kW (city car engine) | 134.102 | 135.962 | 341,214 |
| 250 kW (industrial drive) | 335.256 | 339.905 | 853,035 |
Formulas
- Conversion through the base unit
x = value × f_from ÷ f_to- Watts per unit (the factor table)
hp 745.6999 · PS 735.4988 · BTU/h 0.2930711 · ton 3,516.853 · kcal/h 1.163 · kW 10³ · MW 10⁶- The everyday anchors
1 kW ≈ 1.34102 hp ≈ 3,412.14 BTU/h; 1 ton = 12,000 BTU/h ≈ 3.51685 kW
Standards & References
- NIST SP 811, Guide for the Use of the International System of Units, Appendix B — conversion factors (horsepower 550 ft·lbf/s = 7.456999×10² W; metric horsepower 7.354988×10² W; BTU_IT/h 2.930711×10⁻¹ W; ton of refrigeration 3.516853×10³ W)
- Exact definition: 1 kcal (IT)/h = 4,186.8 J ÷ 3,600 s = 1.163 W
- Unit conversion only — motor output ratings, SAE-vs-DIN engine test bases, and input-vs-output boiler ratings add efficiency questions on top
Frequently Asked Questions
How do I convert kW to HP?
Divide kilowatts by 0.7456999 (or multiply by 1.34102) for mechanical horsepower: 100 kW ≈ 134.1 hp. For metric horsepower (PS) divide by 0.7354988 instead, giving 136.0 PS for the same 100 kW. Going the other way, 1 hp = 0.7457 kW and 1 PS = 0.7355 kW.
What is the difference between HP and PS (metric horsepower)?
Mechanical horsepower is defined as 550 ft·lbf/s = 745.6999 W; metric horsepower (PS, from German Pferdestärke) is 75 kgf·m/s = 735.4988 W. The gap is 1.4% — a "300 PS" European engine is 296 hp. US motor nameplates and pump curves mean mechanical hp; European and Japanese engine brochures mean PS. The converter lists both so the choice is explicit instead of silent.
What is a ton of refrigeration?
The cooling rate that melts one US short ton of ice in 24 hours — standardized as exactly 12,000 BTU (IT)/h = 3,516.853 W ≈ 3.517 kW. Air-conditioning equipment in North America is still sized in tons: a typical house needs 2–5 tons, and the chart's 10 kW row (≈2.84 tons) is squarely residential scale. Note it is a rate of heat removal, not an amount of energy.
How many BTU per hour is a kilowatt?
1 kW = 3,412.14 BTU/h (1,000 W ÷ 0.2930711 W per BTU/h). That is the number for converting electric heater ratings: a 1,500 W space heater delivers about 5,118 BTU/h. For cooling equipment, divide BTU/h by 12,000 to get tons: 36,000 BTU/h = 3 tons ≈ 10.55 kW.
Does converting an engine's kW rating to hp change the measured power basis?
No — the unit conversion is exact, but the RATING may not be comparable. Engine figures depend on the test standard (SAE gross vs net, DIN, JIS), and electric-motor horsepower is shaft output while a heater's kW is input. Convert the number with this tool, then confirm both figures were measured on the same basis before comparing equipment.