Work Calculator
Calculate the mechanical work done by a force, W = F × d × cos θ, or solve the same equation for the force, distance or angle. Use newtons, pounds-force, metres, feet and get the answer in joules, kWh, foot-pounds and more.
0° = force along the motion, 90° = perpendicular (no work)
Adds the average power P = W ÷ t
How to use the Work Calculator
- Choose what to solve for: work, force, distance or angle.
- Enter the known values and pick their units.
- Set the angle between the force and the direction of motion (0° if they point the same way).
- Optionally add a time to also get the average power.
- Read the result in several energy units, with the working and a table of work at other angles.
The work formula
In physics, work is the energy transferred when a force moves an object. For a constant force the work is
W = F × d × cos θ
where F is the size of the force, d the distance moved (displacement) and θ the angle between the force and the direction of motion. Only the force component along the motion, F cos θ, does work. Rearranged, the same equation gives F = W ÷ (d cos θ), d = W ÷ (F cos θ) and θ = arccos(W ÷ (F d)).
- θ = 0°: force along the motion, W = F × d (maximum positive work).
- θ = 90°: force perpendicular to the motion, W = 0.
- θ = 180°: force opposite to the motion (friction, braking), W = −F × d.
Worked example: pulling a sled 25 m with an 80 N rope at 30° above the ground gives W = 80 × 25 × cos 30° = 80 × 25 × 0.8660 ≈ 1,732 J.
Energy unit conversions
| Unit | In joules | Notes |
|---|---|---|
| 1 joule (J) | 1 J | = 1 N·m = 1 W·s |
| 1 kilojoule (kJ) | 1,000 J | |
| 1 foot-pound (ft-lb) | 1.355818 J | 1 lbf moved 1 ft |
| 1 calorie (cal) | 4.184 J | thermochemical calorie |
| 1 kilocalorie (kcal) | 4,184 J | the "Calorie" on food labels |
| 1 BTU | 1,055.06 J | International Table BTU |
| 1 watt-hour (Wh) | 3,600 J | |
| 1 kilowatt-hour (kWh) | 3,600,000 J | unit on electricity bills |
Force conversions used: 1 lbf = 4.448222 N, 1 kgf = 9.80665 N, 1 kN = 1,000 N.
Work, energy and power
The work-energy theorem says the net work done on an object equals its change in kinetic energy, Wnet = ΔKE. Work done against gravity is stored as potential energy, W = m g h. Power is the rate of doing work, P = W ÷ t, measured in watts (1 W = 1 J/s); one mechanical horsepower is about 745.7 W.
Frequently asked questions
What is the formula for work?
Work done by a constant force is W = F × d × cos θ, where F is the force, d is the displacement and θ is the angle between the force and the direction of motion. When the force points along the motion (θ = 0°), cos θ = 1 and W = F × d.
What is the unit of work?
The SI unit of work is the joule (J). One joule is the work done by a force of one newton moving its point of application one metre: 1 J = 1 N·m. In US customary units work is often given in foot-pounds (1 ft-lb ≈ 1.3558 J).
Why does the angle matter?
Only the part of the force that points along the motion does work. That component is F × cos θ. At 90° (a force perpendicular to the motion, like carrying a bag horizontally at constant height) cos θ = 0, so the force does no work.
Can work be negative?
Yes. If the angle is between 90° and 180° the force opposes the motion and the work is negative, meaning it removes energy from the object. Friction and braking forces do negative work.
How do I convert joules to kWh?
Divide by 3,600,000, because 1 kWh = 1,000 W × 3,600 s = 3.6 million joules. For example, lifting 100 kg by 10 m takes about 9,807 J, which is only 0.0027 kWh.
What is the difference between work and power?
Work is the energy transferred (joules); power is how fast it is transferred (watts = joules per second). Doing 1,000 J of work in 2 seconds is an average power of 500 W. Enter a time in the calculator to see the power.
How much work is done lifting an object?
Lifting at constant speed needs a force equal to the weight, F = m × g, so the work is W = m × g × h. Lifting 20 kg by 1.5 m takes 20 × 9.80665 × 1.5 ≈ 294 J.