Formula for Engravable Bounding Box

I’m only aware of Engrave or Cut and Speed as affecting the usable bed size. And it’s not a linear formula. They seem to adjust the horizontal size depending on speed bands. But to get you close…

As of 7/9/2018
Cuts have a bed size of 10.95” x 19.45” maximum. Speed is not a factor for a cut.
Engrave size will depend on the speed from 100 to 1000.
Engrave with speed below 145 allows 10.95” x 19.45” (maximum engrave bed size)
Engrave with speed at 1000 allows 10.95" x 18.05" (the minimum engrave bed size)
800 allows ~18.5"
500 allows ~19"
250 allows ~19.25"

In practice you may not be able to achieve these sizes, because it is extremely difficult to precisely nudge the maximum size in both directions using only the bed camera. Only the horizontal direction is affected by speed. If you have both a cut and an engrave, the bed will be restricted to the lower engrave size for everything.