What Is a Power Converter?
A power converter translates rates of energy transfer between units. Power is energy divided by time, so it measures how fast work gets done. The watt is the SI unit, defined as one joule per second. Horsepower predates the metric system and survives in automotive, marine, and small engine specs. BTU per hour dominates HVAC ratings. These units rarely appear together in one document, which is why a converter is useful when you cross between fields.
You need power conversion when comparing a 150 hp car engine to its kilowatt rating on a European spec sheet, sizing a generator in watts against an air conditioner rated in BTU/h, or checking whether a 2,000-watt microwave will trip a 15-amp circuit. For the energy totals behind these power figures, see our Energy Converter.
What This Calculator Does
This converter handles eight common power units: watts, kilowatts, megawatts, mechanical horsepower, metric horsepower (PS), foot-pounds per second, BTU per hour, and BTU per minute. Enter a value, pick the source and target units, and the result appears instantly. A swap button reverses the direction, and a full table shows your input in every supported unit at once.
- Inputs: A numeric value, source unit, and target unit
- Outputs: Converted result, conversion details, and a table of all units
How the Conversion Works
The calculator first converts the input to watts, the SI base unit for power, then divides by the target unit's watt factor. One watt is one joule per second. Mechanical horsepower is defined as exactly 745.6998715822702 watts, a value set by the 1959 yard and pound agreement. Metric horsepower (PS, from the German Pferdestärke) is defined as exactly 735.49875 watts, based on lifting 75 kilograms at one meter per second against standard gravity.
For example, converting 200 mechanical horsepower to kilowatts: 200 times 745.6998715822702 equals 149,139.97 watts. Dividing by 1,000 gives 149.14 kW. That is why a 200 hp engine is often listed as roughly 149 kW on European spec sheets. For electrical power calculations involving voltage and current, see our Ohm's Law Calculator and Watt Calculator.
Mechanical vs Metric Horsepower
There are two common horsepower definitions, and they are not the same. Mechanical horsepower (also called imperial or brake horsepower) is 745.7 watts. Metric horsepower (PS, CV, ch) is 735.5 watts. The 1.4% difference means a 100 PS European car has about 98.6 mechanical horsepower. American and British sources use mechanical hp. Most of Europe and Japan use PS or CV. Always check which one a spec sheet uses before comparing. This converter includes both so you can move between them.
Common Conversion Factors
| Unit | In Watts | Typical Use |
|---|---|---|
| 1 Watt (W) | 1 | SI base unit, electronics |
| 1 Kilowatt (kW) | 1,000 | EV motors, appliances |
| 1 Megawatt (MW) | 1,000,000 | Power plants, wind turbines |
| 1 Horsepower (hp, mech) | 745.70 | US/UK engines, motors |
| 1 Metric hp (PS / CV) | 735.50 | European/Japanese engines |
| 1 Foot-pound/second | 1.35582 | Mechanical engineering |
| 1 BTU/hour | 0.29307 | HVAC, heating, cooling |
| 1 BTU/minute | 17.584 | HVAC, industrial |
How to Use the Calculator
- Enter the power value you want to convert.
- Select the unit you are converting from.
- Select the unit you are converting to, or click swap to reverse the direction.
- Read the result and the full conversion table below it.
Example Calculations
Example 1: Car Engine hp to kW
A U.S. car is rated at 180 mechanical horsepower. The owner wants the kilowatt figure for a European registration document.
- Start: 180 hp times 745.70 = 134,226 watts
- Convert: 134,226 / 1,000 = 134.23 kW
- In metric hp: 134,226 / 735.50 = 182.5 PS
- Result: 180 hp is 134.2 kW or 182.5 PS
Example 2: Air Conditioner BTU/h to Watts
A portable air conditioner is rated at 14,000 BTU per hour. The user wants the wattage to estimate electricity cost.
- Start: 14,000 BTU/h times 0.29307 = 4,103 watts
- In kilowatts: 4.10 kW of cooling capacity
- Note: this is cooling output. With a CEER of 6.5, electrical input is about 2,154 watts (14,000 / 6.5).
Real-World Scenarios
Generator Sizing for a Job Site
Tom, a contractor in Denver, needs a portable generator to run a 1,500-watt circular saw, a 600-watt air compressor, and a 1,000-watt work light simultaneously. The total running load is 3,100 watts, and he needs about 2,000 additional watts of surge capacity for motor startup. He is looking at a generator rated at 6,500 watts, which the manufacturer also lists as 8.7 hp. Using the converter, he confirms 8.7 mechanical horsepower times 745.70 equals 6,488 watts, which matches the rating. He then checks the BTU/h equivalent for the heat output: 6,500 watts divided by 0.29307 equals 22,180 BTU/h, useful for understanding the cooling load if the generator runs inside an enclosure. For fuel consumption planning, he pairs this with our Fuel Cost Calculator.
EV Motor Comparison Across Markets
Aisha, an automotive journalist, is comparing three electric vehicles for a review. The U.S. spec sheet lists 214 hp. The European version lists 160 kW. The Japanese brochure lists 217 PS. She needs to confirm they are the same motor. Using the converter, 214 mechanical hp equals 159.5 kW, and 160 kW equals 217.5 PS. The three figures describe the same 160 kW motor, rounded differently for each market. She notes that the 1.4% gap between mechanical and metric horsepower means a PS figure is always slightly larger than the equivalent hp figure, which can mislead buyers who compare numbers across regions without converting.
Solar Panel Output to Horsepower
Ken, an off-grid homeowner, has a 6 kW solar array and wants to know how much mechanical work that can drive, to size a water pump. Using the converter, 6,000 watts divided by 745.70 equals 8.05 mechanical horsepower. He picks a 1.5 hp submersible pump (1,118 watts), which his array can run comfortably during peak sun with power to spare for other loads. He also checks the BTU/h equivalent: 6,000 watts times 3.41214 equals 20,473 BTU/h, which tells him the array could theoretically power a small air conditioner, though solar output fluctuates and battery storage is needed for consistent operation. For sizing the battery bank, he uses our Electricity Calculator.
Common Mistakes to Avoid
- Confusing mechanical and metric horsepower: 100 PS is 98.6 hp, not 100 hp. The 1.4% difference seems small but matters in performance comparisons and regulatory paperwork. American specs use mechanical hp (745.7 W). European and Japanese specs use PS or CV (735.5 W). Always confirm which definition a number uses.
- Mixing power and energy: A 1,500-watt heater is rated in power. The energy it consumes depends on how long it runs. 1,500 watts for 4 hours is 6 kWh of energy. You cannot convert watts to BTU (energy) directly. You convert watts to BTU per hour (power), which this calculator does.
- Ignoring input vs output power: An air conditioner's BTU/h rating is cooling output, not electrical input. A 10,000 BTU/h unit with a 10 EER draws 1,000 watts, not 2,930 watts. Efficiency ratios (EER, SEER, COP) bridge the gap. Always check whether a spec is input or output before estimating operating cost.
- Using peak instead of continuous power: Generators and motors often list peak (surge) power separately from continuous (running) power. A 5,000-watt generator may only sustain 4,000 watts continuously. Electric motors need 2 to 3 times their running wattage to start. Size for continuous load plus surge headroom, not the peak number.
Authoritative Research and Resources
- NIST Metric SI Units - The National Institute of Standards and Technology defines the watt as the SI unit of power and maintains reference values for converting between SI and non-SI power units including horsepower and BTU per hour.
- U.S. Department of Energy - Horsepower - The DOE explains the origin and definition of horsepower, its relationship to the watt, and how it is applied in industrial and automotive contexts alongside SI power units.