Router Bushing Calculator
Use this calculator when a guide bushing follows a template and the router bit is smaller than the bushing outside diameter.
Enter a bushing diameter and bit diameter to calculate the offset.
Formula
Offset = (guide bushing outside diameter - router bit diameter) / 2
Template Direction
For inside routing, such as cutting an opening, the template opening needs to be larger than the finished opening by two offsets.
For outside routing, such as following the outside of a pattern, the template needs to be smaller than the finished part by two offsets.