Free Recipe Scaling calculator with clear step-by-step results.
Works from the plate backwards: portions times portion weight is what must be served, grossed up for production loss to give the yield you actually have to make, then divided by the original recipe's yield to give a single multiplier for every ingredient.
Required yield
Yield = portions x portion weight / (1 - process loss)
Scale factor
Factor = required yield / original recipe yield
Trim, evaporation, what stays in the pan, and portioning waste. Six to ten percent is typical for a wet dish; a dry mix can be under two.
Bulk ingredients do. Salt, spice and leavening should be scaled more conservatively, and cooking times will change even though quantities scale cleanly.