What is the lever formula?

For a balanced lever, effort × effort arm = load × load arm, where each arm is the distance from the fulcrum to where that force acts. Know any three values and you can find the fourth.

What are the three classes of levers?

First class: the fulcrum is between the effort and the load (seesaw, crowbar, scissors). Second class: the load is between the fulcrum and the effort (wheelbarrow, nutcracker). Third class: the effort is between the fulcrum and the load (tweezers, a fishing rod, your forearm).

How do you find the mechanical advantage of a lever?

Divide the effort arm by the load arm. An effort arm 4 ft long against a 2 ft load arm gives a mechanical advantage of 2: the effort is half the load, but it has to move twice as far.

Free tool · OAR Mechanical Comprehension

Lever calculator

A balanced lever obeys effort × effort arm = load × load arm. Pick what you want to find, enter the other three values and check the torque balance.

Result

Answer: 150 lb
Mechanical advantage: 2 : 1
Torque check: 150 lb × 4 ft = 300 lb × 2 ft = 600 ft·lb

The effort arm is longer than the load arm, so the lever multiplies force (and the effort moves farther than the load).

How the calculation works

A lever is balanced when the turning effect (torque) on each side of the fulcrum is equal. Torque is force × the distance from the fulcrum, so:

Effort × effort arm = load × load arm
Mechanical advantage = effort arm ÷ load arm

Example: a 300 lb load 2 ft from the fulcrum, with the effort applied 4 ft away: 300 × 2 ÷ 4 = 150 lb. The mechanical advantage is 2 : 1: half the force, but the effort end travels twice as far as the load.

The three classes of levers

Class	What sits in the middle	Examples
First	Fulcrum	Seesaw, crowbar, scissors
Second	Load	Wheelbarrow, nutcracker, bottle opener
Third	Effort	Tweezers, fishing rod, broom, forearm

The formula is the same for all three. Second-class levers always multiply force (the effort arm is the longer one); third-class levers always multiply distance and speed instead.

Test yourself: an OAR-style question

A lever balances a 300 lb load that sits 2 ft from the fulcrum. How much effort force is needed 4 ft from the fulcrum on the other side?

139 lb
154 lb
135 lb
150 lb

Show answer

D. 150 lb

Balance the torques: load × load arm = effort × effort arm, so 300 × 2 = effort × 4 and the effort is 150 lb.

Questions like this come up on the Mechanical Comprehension section of the OAR. The 2,604 questions in the app each come with a written explanation.

FAQ

What is the lever formula?: For a balanced lever, effort × effort arm = load × load arm, where each arm is the distance from the fulcrum to where that force acts. Know any three values and you can find the fourth.
What are the three classes of levers?: First class: the fulcrum is between the effort and the load (seesaw, crowbar, scissors). Second class: the load is between the fulcrum and the effort (wheelbarrow, nutcracker). Third class: the effort is between the fulcrum and the load (tweezers, a fishing rod, your forearm).
How do you find the mechanical advantage of a lever?: Divide the effort arm by the load arm. An effort arm 4 ft long against a 2 ft load arm gives a mechanical advantage of 2: the effort is half the load, but it has to move twice as far.

Sources

Checked against these sources on October 24, 2026. Ideal lever: weightless and rigid, no friction at the fulcrum. For OAR preparation only; not affiliated with or endorsed by the U.S. Navy. Calculations run in your browser.