Archimedes said he could move the Earth with a long enough lever. Seesaws (class I), wheelbarrows (class II) and tweezers (class III) all balance effort and load around a fulcrum by the law of the lever.
How to use the Fulcrum Calculator
- Lever class
- Lever length L
- Load force F_l
- Effort force Fₑ
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose the lever class and enter the lever length, the load and the effort available.
Inputs explained
| Field | What to enter |
|---|---|
| Lever class | Choose one: Class I (fulcrum in the middle), Class II (load in the middle), Class III (effort in the middle) |
| Lever length L | Units: m, cm, mm, km, in, ft … |
| Load force F_l | Units: N, kN, MN, mN, lbf, kgf … |
| Effort force Fₑ | Units: N, kN, MN, mN, lbf, kgf … |
Example values
How the main result changes when Lever length L changes and everything else stays at the example values above:
| Lever length L (m) | Load arm d_l (fulcrum to load) (m) |
|---|---|
| 1 | 0.2857 |
| 1.5 | 0.4286 |
| 2 | 0.5714 |
| 2.5 | 0.7143 |
| 3 | 0.8571 |
| 4 | 1.1429 |
Formula
Fₑ·dₑ = F_l·d_l · Class I: d_l = L·Fₑ/(Fₑ + F_l) · Class II: d_l = L·Fₑ/F_l · Class III: dₑ = L·F_l/Fₑ
Worked example
Inputs — Lever class: Class I (fulcrum in the middle); Lever length L: 2 m; Load force F_l: 500 N; Effort force Fₑ: 200 N.
Results — Load arm d_l (fulcrum to load) = 0.5714 m; Effort arm dₑ (fulcrum to effort) = 1.4286 m; Mechanical advantage = 2.5 ×; Possible? = Yes.
Key terms
- Fulcrum
- The pivot point of a lever.
Frequently asked questions
What are the three classes of levers?
They differ by whether the fulcrum, load or effort is in the middle.
Can a class III lever give mechanical advantage?
No – it trades force for speed and range of motion.
Why is a wheelbarrow class II?
The load sits between the wheel (fulcrum) and your hands.
Does the lever's weight matter?
Yes in practice; this calculator assumes a weightless lever.