"Lloyd E. Sponenburgh"
wws

Roll the cutter on a flat surface one
revolution and measure it.
Solve for diameter.


Roll? A three-blade carbide wing drill?

You must be assuming all cutters are
helical-flute millers. Not most of
these -- "ROUTER BITS".

LLoyd

Perhaps by using, OMG, trigonometry?
Or plane geometry? horror of horrors...
But it may not be accurate to a 0.001 ....
phil k.