Power Conversion Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: August 19, 2026Two Different Horsepowers, and Both Are in Use
When a European manufacturer quotes 150 PS and an American one quotes 150 hp, those are not the same engine. Mechanical horsepower is 745.6998715822702 watts; metric horsepower (PS, or Pferdestärke) is 735.49875 watts. The gap is about 1.4% — small enough to be ignored casually, large enough to matter in a spec comparison or a homologation document. This converter treats them as the distinct units they are.
The Formula
Power is the rate of energy transfer, and the watt — one joule per second — is the base every unit here pivots through:
(Factors are relative to 1 watt)
Converting 200 hp to kilowatts is 200 × 745.6998715822702 ÷ 1000 = 149.13997432 kW.
The Factors
| Unit | Code | Watts per unit | Basis |
|---|---|---|---|
| Watts | w | 1 | SI: 1 J/s |
| Kilowatts | kw | 1000 | SI multiple |
| Megawatts | mw | 1000000 | SI multiple |
| Horsepower (Mechanical) | hp | 745.6998715822702 | 550 ft·lbf/s |
| Metric Horsepower (PS) | ps | 735.49875 | 75 kgf·m/s |
| BTU/Hour | btu_hr | 0.29307107017222222 | 1 BTU per 3600 s |
| Foot-Pounds/Second | ftlb_s | 1.3558179483314 | 1 ft·lbf per second |
Mechanical horsepower's odd factor traces back to its definition as 550 foot-pounds per second: 550 × 1.3558179483314 = 745.6998715822702 W exactly.
Horsepower and Kilowatts
The conversion that gets run most, in both directions:
| Horsepower | Kilowatts |
|---|---|
| 1 | 0.74569987 |
| 100 | 74.56998716 |
| 150 | 111.85498074 |
| 200 | 149.13997432 |
| 300 | 223.70996147 |
| 500 | 372.84993579 |
| Kilowatts | Horsepower |
|---|---|
| 1 | 1.34102209 |
| 50 | 67.05110448 |
| 100 | 134.10220896 |
| 150 | 201.15331344 |
| 200 | 268.20441792 |
Full Cross-Reference
| 1 of… | Watts | Kilowatts | hp | PS | BTU/hr |
|---|---|---|---|---|---|
| Watt | 1 | 0.001 | 0.00134102 | 0.00135962 | 3.41214163 |
| Kilowatt | 1000 | 1 | 1.34102209 | 1.35962162 | 3412.14163313 |
| Megawatt | 1000000 | 1000 | 1341.0220896 | 1359.6216173 | 3412141.63313 |
| Horsepower (Mechanical) | 745.69987158 | 0.74569987 | 1 | 1.01386967 | 2544.43357764 |
| Metric Horsepower (PS) | 735.49875 | 0.73549875 | 0.98632007 | 1 | 2509.62590599 |
| BTU/Hour | 0.29307107 | 0.00029307 | 0.00039301 | 0.00039847 | 1 |
| Foot-Pound/Second | 1.35581795 | 0.00135582 | 0.00181818 | 0.0018434 | 4.62624287 |
Where the Distinction Counts
- Vehicle and engine specs — comparing a European PS rating against a North American hp rating, or either against a kW figure on an EV.
- HVAC equipment — air conditioners rated in BTU/hour against heat pumps rated in kilowatts. The 3412.14163313 BTU/hr per kW factor is the bridge.
- Electric motors — industrial motors are nameplated in hp in some markets and kW in others, and drive sizing depends on getting it right.
- Generators and plant capacity — output in megawatts translated to horsepower for mechanical comparison.
- Mechanical work rate — foot-pounds per second appearing in older engineering texts alongside modern watt figures.
How to Use This Calculator
- Enter the power figure in the Value field.
- Select the source unit in the first dropdown — check whether a horsepower figure is mechanical hp or metric PS before choosing.
- Select the target unit in the second dropdown.
- Press Calculate. The breakdown lists both watt factors and the division.
Related Calculations
Power sustained over time gives energy — the Energy Conversion Calculator covers joules, kWh and BTU. For data throughput rather than electrical power, see the Data Transfer Rate Converter.
Governing Principles of Physical Power and Conversion Scales
Power represents the time rate of performing mechanical work or converting energy from one form to another: P = dE/dt. In the International System of Units (SI), the standard coherent unit of power is the Watt (W), named in honor of Scottish engineer James Watt. One Watt represents the transfer of one Joule of energy per second (1 W = 1 J/s = 1 N·m/s = 1 kg·m²/s³).
Industrial machinery, automotive engineering, HVAC refrigeration, electrical grid distribution, and acoustics employ diverse regional and historical units of power. Precision engineering requires understanding exact conversion factors between SI metric units, imperial horsepower standards, and thermodynamic heat transfer ratings.
Comprehensive Power Conversion Equivalency Matrix
| Power Unit | Symbol | Equivalent in Watts (SI) | Primary Industry or Application |
|---|---|---|---|
| Watt (SI Base) | W | 1.000 W (1.0 J/s) | Scientific physics, audio engineering, electronics |
| Kilowatt | kW | 1,000 W (10³ W) | Electric motors, household appliances, EV charging |
| Megawatt / Gigawatt | MW / GW | 106 W / 109 W | Hydroelectric dams, thermal power plants, regional utility grids |
| Mechanical Horsepower (Imperial) | hp (I) | 745.69987 W (550 ft·lbf/s) | American automotive engines, pumps, industrial compressors |
| Metric Horsepower (PS / DIN) | PS / cv / pk | 735.49875 W (75 kgf·m/s) | European and Japanese automotive engine ratings |
| Electrical Horsepower | hp (E) | 746.00000 W | Electric motor nameplate ratings in North America |
| Boiler Horsepower | BHP | 9,809.50 W (33,475 BTU/h) | Industrial steam boiler evaporation capacity |
| Ton of Refrigeration | TR / RT | 3,516.853 W (12,000 BTU/h) | Commercial HVAC chillers and industrial cold storage |
| BTU per Hour | BTU/h | 0.2930711 W | Residential furnaces, gas water heaters, air conditioners |
| Decibel-Milliwatt | dBm | P(W) = 10(dBm-30)/10 | RF telecommunications, Wi-Fi router transmit power |
Step-by-Step Worked Calculation Example
Example: Electric Vehicle Motor Power Rating Conversion
Problem: An all-electric performance vehicle traction motor has a peak manufacturer power rating of 320.0 kilowatts (kW). Convert this output power rating into: (1) Imperial mechanical horsepower (hp); (2) Metric horsepower (PS); and (3) BTU per hour (BTU/h) for thermal cooling system sizing.
Step 1: Convert kilowatts to imperial mechanical horsepower:
Power in hp = 320,000 W / 745.69987 W/hp = 429.13 hp
Step 2: Convert kilowatts to metric horsepower (PS):
Power in PS = 320,000 W / 735.49875 W/PS = 435.08 PS
Step 3: Convert kilowatts to BTU per hour:
Power in BTU/h = 320,000 W / 0.2930711 W/(BTU/h) = 1,091,885 BTU/h (1.092 MMBTU/h)
Conclusion: The 320 kW motor outputs 429.1 hp (435.1 PS), dissipating thermal rejection equivalent to 1.09 million BTU/h under peak load.
Common Pitfalls in Power Conversion
- Confusing Imperial Mechanical Horsepower with Metric PS: European vehicle specs state horsepower in PS (735.5 W); directly converting to imperial hp (745.7 W) without adjusting overstates power by approximately 1.4%.
- Ton of Refrigeration vs. Mass Ton: A "ton of refrigeration" is a power rate (3.517 kW — the rate of heat extraction needed to freeze 1 short ton of water into ice in 24 hours), not a measure of physical weight.
Marine Propulsion and Gas Turbine Shaft Ratings
In naval architecture and marine engineering, ship propulsion systems (such as modern container vessels and naval frigates) express main engine output in shaft horsepower (shp) and brake horsepower (bhp), where 1 shp equals 745.7 Watts delivered directly to the propeller drive shaft. Marine diesel two-stroke engines on ultra-large container ships produce over 80,000 kW (approx. 107,000 bhp), driving massive fixed-pitch propellers at 80 RPM with thermal brake efficiencies exceeding 50%.
Aviation Jet Engine Thrust vs. Equivalent Shaft Power
Turbofan jet engines measure thrust in kiloNewtons (kN) or pounds-force (lbf). At high flight cruising speeds, net propulsive thrust power is calculated via P = Thrust × True Airspeed: a jet engine delivering 120 kN of net thrust at 250 m/s cruise speed produces 30.0 Megawatts (approx. 40,200 hp) of continuous kinetic propulsion power.