How this calculator works
A class I lever has the fulcrum between the forces, so its arms add to the full length. In class II the effort sits at the far end and the load lies between it and the pivot. In class III the load sits at the far end and the effort lies between it and the pivot. Forces are perpendicular to a straight, weightless bar. Class constraints prevent a calculated force arrangement from silently becoming another lever class.
Formula
Fe de = Fr dr; MA = Fr/Fe = de/dr. Class I: L = de+dr; class II: L = de; class III: L = dr.
Worked example
A 4 m class I lever balancing a 300 N load with 100 N effort has a 1 m load arm and a 3 m effort arm. A 2 m class II lever with a 200 N load and 100 N effort has a 1 m load arm.
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Frequently asked questions
Where is the fulcrum coordinate measured from?
The outputs give distances from the pivot to each force. Class I places the pivot between them; classes II and III put it at one end.
Why must class III have advantage below one?
Its effort acts closer to the pivot than its load, trading force for motion.
Does the tool include the bar's own weight?
No. A heavy bar adds a moment through its centre of mass and changes the balance.