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Efficiency calculator

Compute efficiency as the ratio of useful output to total input.

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Enter Useful output energy, Total input energy and the Efficiency calculator works out Efficiency straight away. For instance, with Useful output energy = 80 and Total input energy = 100 it returns Efficiency = 80%.

How to use it

  1. Enter your values: Useful output energy, Total input energy.
  2. Read the result instantly: Efficiency.

Frequently asked questions

How does the Efficiency calculator work?

It takes Useful output energy and Total input energy and derives Efficiency from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

2 values: Useful output energy and Total input energy. Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Useful output energy = 80 and Total input energy = 100, the calculator returns Efficiency = 80%. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

When would I actually use this?

Checking a homework answer, sizing something before building it, and getting an order of magnitude before committing to a design — a torque on a bolt, the force a spring returns, the frequency a circuit resonates at, how long light takes to arrive.

What is the most common mistake?

Feeding in a value in the wrong unit. Physics formulas assume SI throughout, so grams instead of kilograms or centimetres instead of metres shifts the answer by powers of ten without any warning.

What is the difference between the Efficiency calculator and the Kinetic energy calculator?

This one returns Efficiency; the Kinetic energy calculator returns Kinetic energy (J). That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Potential energy calculator is the closest one after this: Compute gravitational potential energy from mass, height and gravity (E = mgh).

What else is worth having open alongside it?

Specific heat calculator and Spring potential energy calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from, and how current are they?

Constants are the CODATA values and the formulas are the textbook ones. Most assume an idealised case — no air resistance, no friction, a point mass — and the tool says so where the simplification matters.

Further reading

All guides →
ExplainerHooke's Law Explained: F = kx, Real Spring Constants, and Where It Stops HoldingHooke's law says force is proportional to stretch — but only below the elastic limit. Here is F = kx with worked numbers, what a 200 N/m spring actually feels like, and how springs combine.GuideThe Four Kinematics Equations: Which One to Use, and What Each One Leaves OutFive variables, four equations, and each equation is missing exactly one of them. Choose by looking at the variable the question never mentions.ExplainerProjectile Motion Explained: Range, Height, Flight Time — and Why 45° Is Not Always BestThree formulas cover the whole of projectile motion on level ground. The catch is level ground: the moment launch and landing heights differ, the 45° result stops being true.ExplainerWhat Is Kinetic Energy? The KE = ½mv² Formula ExplainedKinetic energy is the energy of motion, given by KE = ½mv². Learn what the formula means, why speed matters most, and see worked examples in joules.ExplainerWhat Is Horsepower? Mechanical hp, Metric PS, and kWHorsepower measures the rate of doing work. Learn where the unit came from, how mechanical hp differs from metric PS/CV, and how both relate to kilowatts.ExplainerHow the Doppler Effect Works: The Formula, the Sign Convention, and Why Moving the Source Is Not the Same as Moving the ListenerFor sound, f' = f(v + v_o)/(v − v_s) — and getting the signs backwards is the classic error. Here is the convention spelled out, a 440 Hz source computed at four speeds, and why light needs a different equation entirely.