Code says there should be a power receptacle about every six
feet along wall. Therefore power cords are generally about 6
feet long. Maybe 8 foot max to provide a margin of
adjustment.

Too_Many_Tools wrote:
In about a month, I will be replacing a significant number of power
cords on a variety of metal and wood working machines.

So how long of a cord should a person replace them with?

It's a harder question to answer than at first glance. It's like asking
"How high should I build my workbench?"..it depends.

Of course one should replace the cord so the new one reaches the outlet
but how much extra cord should one allow?