About this calculator
Power is the rate of doing work. The same job done twice as fast needs twice the power. This calculator covers four everyday cases: pushing or pulling something at a steady speed (conveyors, winches, vehicles), a known amount of work in a known time, a constant force moving a load through a distance, and lifting a load to a height (hoists, lifts, pumps lifting water).
Formula
Force × speed
P = F × v
F = force (N), v = speed (m/s), P = power (W).
Work ÷ time
P = W ÷ t
W = work or energy (J), t = time (s).
Force × distance
W = F × d P = W ÷ t
F = constant force (N) acting in the direction of motion, d = distance moved (m), W = work (J), t = time taken (s), P = average power (W). If the force acts at an angle θ to the motion, only F cos θ does work.
Lifting a load
W = m × g × h P = W ÷ t
g = 9.80665 m/s² (standard gravity). Input power = P ÷ efficiency.
Worked example
- Force × speed: 1000 N at 2 m/s = 2000 W = 2 kW.
- Work ÷ time: 3.6 kJ in 60 s = 60 W.
- Force × distance: a steady 1000 N pull moves a trolley 5 m in 60 s: work = 1000 × 5 = 5000 J; power = 5000 ÷ 60 = 83.3 W.
- Lifting: 1000 kg raised 10 m in 20 s: work = 1000 × 9.80665 × 10 = 98 067 J; power = 98 067 ÷ 20 = 4.90 kW. With an 80% efficient hoist, the motor must supply 4.90 ÷ 0.8 = 6.13 kW.
Assumptions and limitations
- Steady motion. Acceleration, starting loads and friction outside the drive efficiency are not included — add a margin when selecting a motor.
- Force × distance mode assumes a constant force acting along the direction of motion. For a changing force the work is the area under the force–distance graph; for rotating parts use the torque and shaft power calculator.
- Lifting mode ignores the weight of hooks, ropes and counterweights.
Safety note
Motor and hoist selection for lifting equipment must follow the applicable lifting-equipment standards and include their safety factors.
References
- Definitions of work and power (ISO 80000-4); standard gravity 9.80665 m/s².