rpm to fpm on a sawmill OnlineConversion Forums20/03/2015· To convert that to an rpm we need to divide by the circumference of the wheel pi x diameter If the wheel is the same diameter as the 19 pulley then we need 844 rpm If it is NOT 19 you need to tell us or work through the rpm yourself We set up a proportion x inches/19 inches = 844 rpm/3100 rpm so x = inches You would then come