Block and Tackle Mechanical Advantage Calculator

A block and tackle shares a load across however many rope segments run between the fixed and moving blocks. Ignoring friction, pulling the rope a given distance moves the load only 1/n as far, so by the work-in = work-out rule of simple machines, the ideal mechanical advantage is exactly n — the number of supporting rope segments — and the ideal effort needed is the load force divided by n.

Real rigging loses some of that advantage to friction at each pulley sheave and rope bend, captured here by a system efficiency percentage you supply (100% models an idealized, frictionless system). Friction makes the actual required effort larger than the ideal effort by that same factor — actual effort = ideal effort ÷ efficiency — which is equivalent to saying the actual mechanical advantage is only n × efficiency instead of the full n.

Both the mechanical advantage and effort calculations are scale-invariant ratios, so the effort force comes out in whichever force unit the load was given in — no internal metric-to-imperial conversion of the force value itself is needed.