Power Converter
Convert power between watts, kilowatts, horsepower and BTU/hour.
Results update as you type.
About this calculator
A power converter changes a rate of energy use — energy per unit time — between watts, kilowatts and megawatts, mechanical and metric horsepower, and BTU per hour. All values convert through the watt as a common base.
The figures to know are 1 mechanical horsepower ≈ 745.7 watts, 1 metric horsepower (PS) ≈ 735.5 watts, and 1 watt ≈ 3.412 BTU/hour. The two horsepower definitions differ by about 1.4%, which is why the same engine can be quoted at two slightly different hp numbers.
Worked example: to convert 150 kilowatts to horsepower, divide by 0.7457, giving about 201 hp — a typical electric-car motor rating. To size an air conditioner, a 3.5 kW unit is 3,500 × 3.412 ≈ 12,000 BTU/hour, a "1 ton" cooler. A results table shows the same power in every unit at once.
Frequently asked questions
How many watts are in one horsepower?
One mechanical horsepower is about 745.7 watts. Metric horsepower (PS) is slightly less, about 735.5 watts, which is why the same engine can show two different figures.
How do kilowatts relate to horsepower?
One kilowatt is about 1.341 mechanical horsepower. Electric-car motors are often rated in kW, so a 150 kW motor is roughly 201 hp.
What is BTU per hour?
BTU/hour rates heating and cooling equipment. One watt equals about 3.412 BTU/h, so a 3.5 kW air conditioner is roughly 12,000 BTU/h — a "1 ton" unit.
What is the difference between mechanical and metric horsepower?
Mechanical (imperial) horsepower is about 745.7 watts, while metric horsepower, also called PS or CV, is about 735.5 watts — roughly 1.4% less. Car makers in different regions quote whichever suits them, so this power converter offers both.
How many watts does one horsepower equal?
One mechanical horsepower is about 745.7 watts, so a 100 hp engine produces roughly 74.6 kilowatts at its rated output.
How do I convert kW to BTU per hour?
Multiply kilowatts by 3,412.14. So a 2 kW heater outputs about 6,824 BTU/hour, the way heating and cooling equipment is usually rated in North America.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/power/curl
curl "https://calculator.free/api/v1/power/?amount=1&from=kw&to=hp"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/power/?" + new URLSearchParams({
"amount": "1",
"from": "kw",
"to": "hp"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.