Lever Calculator
Calculate lever mechanical advantage, effort force, load force, and lever arm lengths using the law of the lever Fa × a = Fb × b. Free online physics calculator.
Enter any 3 values. The unknown value is calculated using Fa × a = Fb × b.
About This Calculator
The Lever Calculator helps you analyze any lever system using the fundamental law of the lever discovered by Archimedes. Enter any three values — effort force, effort arm length, load force, or load arm length — and the calculator instantly computes the missing value along with the mechanical advantage.
A lever is one of the six classical simple machines. It consists of a rigid beam or rod that pivots about a fixed point called the fulcrum. The lever equation Fa × a = Fb × b describes the equilibrium condition, where Fa is the effort force applied, a is the distance from the fulcrum to the point of effort, Fb is the load force, and b is the distance from the fulcrum to the load. The mechanical advantage (MA = a / b) tells you how effectively the lever multiplies force.
There are three classes of levers based on the relative positions of the fulcrum, effort, and load. Class I levers have the fulcrum between effort and load (seesaw, crowbar). Class II levers have the load between fulcrum and effort, always providing a mechanical advantage greater than 1 (wheelbarrow, bottle opener). Class III levers have the effort between fulcrum and load, giving a mechanical advantage less than 1 but increasing speed and range of motion (tweezers, fishing rod).
This calculator is ideal for physics students, engineering professionals, and anyone working with mechanical systems. It supports worldwide use with consistent SI units (Newtons and meters).
Frequently Asked Questions
What is a lever and how does it work?
A lever is a simple machine consisting of a rigid bar that pivots around a fixed point called the fulcrum. It works by applying a small force (effort) over a longer distance to move a larger load over a shorter distance, or vice versa, following the law of the lever: Fa × a = Fb × b.
What is the law of the lever formula?
The law of the lever states that the effort force multiplied by the effort arm length equals the load force multiplied by the load arm length: Fa × a = Fb × b. This equilibrium equation allows you to calculate any unknown quantity when three values are known.
What is mechanical advantage of a lever?
Mechanical advantage (MA) of a lever is the ratio of the effort arm length to the load arm length (MA = a / b). A mechanical advantage greater than 1 means the lever multiplies force, allowing you to lift heavy loads with less effort. An MA less than 1 means the lever increases speed at the expense of force.
What are the three classes of levers?
Class I levers have the fulcrum between the effort and load (e.g., seesaw, crowbar, scissors). Class II levers have the load between the fulcrum and effort, with effort arm longer than load arm (e.g., wheelbarrow, bottle opener, nutcracker). Class III levers have the effort between the fulcrum and load, with load arm longer than effort arm (e.g., tweezers, fishing rod, baseball bat).
How do I use the lever calculator?
Enter any three of the four values: effort force (Fa), effort arm length (a), load force (Fb), and load arm length (b). Leave the unknown field empty or set to zero. Click Calculate and the calculator will compute the missing value using Fa × a = Fb × b, along with the mechanical advantage.
What units does the lever calculator use?
The calculator uses Newtons (N) for force values and meters (m) for arm lengths. You can use any consistent units as long as you are consistent across all inputs — the mechanical advantage is a dimensionless ratio and remains correct regardless of units.
Can I share my lever calculation results?
Yes, all input values are saved in the URL as query parameters. You can copy the URL and share it with others. When they open the link, the calculator will automatically restore your inputs and compute the results.
What is a real-world example of a lever?
A common example is a seesaw on a playground. If a 75 kg person sits 1.6 m from the fulcrum and a 60 kg person sits 2 m from the fulcrum on the other side, the seesaw balances. The mechanical advantage is 0.8, meaning the heavier person must sit closer to the fulcrum to balance the lighter person.