There are a few ways to measure the Overlap %, which is a percentage of the overlap within the seam.
The most common formula to calculate Overlap % is:
Overlap % = Overlap / Dim B
Additional formulas such as:
Overlap % (1.1x) = (1.1 Cover-thick + cover-hook + body-hook – length) / (Length – (2.2 cover-thick + 1.1 body-thick))
There are additional ways to calculate this (e.g., using Ferrolite) and with different factors.