Power Calculator (P = W/t)
Calculate mechanical power in Watts and horsepower. Enter work done and time, or force and distance (at constant speed) and time.
How to use this tool
- Enter work done (w), time, force (optional, instead of w) and distance (if using force) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your power and the full breakdown beneath it.
Power is the rate of doing work: P = W/t (Watts = Joules per second). Alternatively P = F·v for constant speed. One horsepower = 745.7 W.
Formula
P = W ÷ t
Alternatively: P = F × d ÷ t (if force and distance are given instead of work)
Horsepower: hp = P ÷ 745.7
Where P = power (W), W = work (J), t = time (s), F = force (N), d = distance (m).
How it works
This calculator computes mechanical power — the rate at which work is done or energy is transferred. If force and distance are provided instead of total work, it first computes work as F × d, then divides by time. It also converts Watts to mechanical horsepower (1 hp = 745.7 W). The formula assumes a constant force and constant speed; instantaneous power in systems with varying force or velocity requires calculus.
Worked example
- Given: work W = 1000 J, time t = 10 s.
- Apply: P = W ÷ t = 1000 ÷ 10 = 100 W.
- Convert to horsepower: hp = 100 ÷ 745.7 ≈ 0.1341 hp.
Power = 100 W; Horsepower = 0.1341 hp
Common mistakes to avoid
- Entering force and distance as a shortcut without checking that the force is constant over that distance -- average power from F x d / t is only valid for constant force.
- Confusing electrical power (P = VI) with mechanical power (P = W/t) -- this calculator uses the mechanical definition only.
- Entering time in minutes instead of seconds -- 2 minutes must be entered as 120 s; using 2 overstates power by 60x.
Key terms
- Power
- The rate of doing work or transferring energy. Measured in Watts (W), where 1 W = 1 J/s.
- Watt (W)
- The SI unit of power. 1 Watt equals 1 Joule of energy transferred per second.
- Horsepower (hp)
- A non-SI unit of power commonly used for engines. One mechanical horsepower equals 745.7 W.
- Work (J)
- The energy input or output over the time period. Power is the work divided by the time taken to do it.
- Rate of energy transfer
- Power describes how quickly energy moves — a high-powered machine does the same work as a low-powered one, but in less time.
Frequently asked questions
- What is the difference between power and energy?
- Energy (J) is the total amount of work done; power (W) is how fast it is done. A 100 W bulb running for 36,000 s uses 3,600,000 J = 1 kWh.
- How do I convert watts to horsepower?
- Divide watts by 745.7. A 1000 W motor produces about 1.34 hp.