How long of a belt do I need for my lawnmower?

Question

I think the original belt was a 42 inch but I replaced a pulley from 5 inches to 3 inches how long of a belt will I need now?

Answer 1

This sounds like a homework problem to me. Why would you replace the pulley to a smaller one?  Which belt? Is it 180 deg. contact or an idler pulley with less?  

Answer 2

Maybe 3" less or so, half the circumference difference of the 5" and 3" pulleys.

Try measuring it. Measure from the outside of each pulley and around, then multiply by 2. This would be your belt length. Or use a rope to measure the entire path.

Answer 3

The best way is to take a piece 3/8" rope and wrap it around the pulleys- the path of the v-belt, mark where the two ends overlap measure that length, that will be the size belt you need