How to use this calculator
- Enter or choose calculate from.
- Enter or choose power unit.
- Enter or choose time (duration).
- Enter or choose time unit.
- The result updates as you type. Use Copy result or Share to keep it.
Method
P = W ÷ t; W = P t; t = W ÷ P; P = F v
- P
- power in watts (1 hp = 745.700 W; 1 PS = 735.499 W)
- W
- work or energy in J
- t
- time in s
- F
- force along the motion in N
- v
- speed in m/s
Worked example
- P = W ÷ t.
- P = 6,000 J ÷ 20 s = 300 W (0.3 kW, about 0.40 hp).
Doing 6,000 J of work in 20 seconds takes 300 W of mechanical power.
What the result means
This is output (useful) power. A motor or engine must draw more input power than this because of its efficiency losses; divide by the efficiency to size the drive. For torque and rpm, use the Horsepower Calculator.
Assumptions and limits
- Average power over the stated time; force and speed along the same line.
- Peak power during acceleration can be much higher than the average.
Questions
How many watts is one horsepower?
Mechanical (imperial) horsepower is 550 ft·lbf/s = 745.700 W. Metric horsepower (PS) is 75 kgf·m/s = 735.499 W.
Why use P = F v?
For steady motion it avoids needing a time: a cyclist pushing 20 N of drag at 10 m/s needs 200 W.