Car Weight Calculator

Find how heavy an HO freight or passenger car should be so it rolls and tracks reliably, using the NMRA RP-20.1 recommendation. Pick the car that looks like yours, or measure your own.

RP-20.1 for HO is 1 oz plus 0.5 oz for each inch of car body length (measured over the body, not the couplers). It is a tracking guideline, not a prototype-mass figure — weight added low in the frame keeps a car planted in curves. See the glossary for the physics, or grab weights in the store.