Power Converter
Convert power between watts, kilowatts, megawatts, horsepower, BTU per hour, and calories per second.
How to use this tool
- Enter power and from unit in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your horsepower and the full breakdown beneath it.
Formula
All units convert to watts (W) first, then to the target unit:
W = input × factorfrom
output = W ÷ factorto
Key factors: W = 1 | kW = 1000 W | MW = 1,000,000 W | hp = 745.69987 W | BTU/h = 0.29307 W | cal/s = 4.184 W
How it works
The watt (J/s) is the SI unit of power — the rate of energy transfer. Each unit has a fixed watt-equivalent; the converter scales to watts then redistributes to all output units. Mechanical horsepower (745.7 W) is the defined standard used here; electrical horsepower and metric horsepower (PS, 735.5 W) are slightly different values used in other contexts.
A common mistake is confusing power (watts, horsepower) with energy (joules, kilowatt-hours): power is a rate, while energy is the accumulated total over time. A 1 kW device running for 1 hour consumes 1 kWh of energy — the two quantities are related by time, not directly interchangeable.
Worked example
Convert 1 kilowatt to all power units
- Input: 1 kW (from_unit = kilowatt), so base in watts = 1 × 1000 = 1000 W.
- MW: 1000 / 1,000,000 = 0.001 MW.
- Horsepower: 1000 / 745.69987 ≈ 1.341 hp.
- BTU/hour: 1000 / 0.29307 ≈ 3412.154 BTU/h. Calories/second: 1000 / 4.184 ≈ 239.006 cal/s.
1000 W | 1 kW | 0.001 MW | 1.341 hp | 3412.154 BTU/h | 239.006 cal/s
Common mistakes to avoid
- Confusing mechanical horsepower (745.7 W) with metric horsepower (735.5 W) -- European car specs often use metric hp (PS/CV), producing a ~1.4% difference that matters in engine comparisons.
- Mixing up power (watts) and energy (watt-hours) -- a 100 W bulb running for 10 hours uses 1 kWh of energy, not 100 kWh.
- Treating BTU/hr as an energy unit rather than a power unit -- air conditioner capacity in BTU/hr is a rate, not a stored amount of energy.
Key terms
- Watt (W)
- The SI unit of power, equal to one joule per second. Named after James Watt.
- Horsepower (hp)
- A unit of power equal to 745.69987 W. Mechanical horsepower was historically defined as the average power output of a draft horse.
- BTU per hour (BTU/h)
- An imperial power unit equal to 0.29307 W, commonly used to rate the heating or cooling capacity of HVAC systems.
- Kilowatt (kW)
- Equal to 1000 watts. The standard unit for rating motors, appliances, and EV charging rates.
Frequently asked questions
- How many watts is one horsepower?
- One mechanical horsepower equals exactly 745.69987 watts. The metric horsepower (PS) is slightly different at 735.499 watts.
- What is the practical difference between kW and kWh on an electricity bill?
- kW is power (how fast energy is used), while kWh is energy (how much was used over time). Your electricity bill charges for kWh: a 2 kW heater running for 3 hours uses 6 kWh.
- Why do electric motors sometimes list power in both kW and horsepower?
- Historically different industries adopted different conventions. Automotive and industrial contexts in the US use horsepower, while the SI system uses kilowatts. Modern standards increasingly prefer kW, but horsepower persists in marketing.