From the Labonville website:
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I followed the directions and measured for the top of my belt to my instep to get 39". I purchased the "XL = 40" length and they are a perfect fit.
**IMPORTANT NOTICE***
Sizing - Chap length is not the same as your pants length. It is not measured by your Inseam. Chaps are sized by overall length. To calculate your overall length measure from your waist (where you would wear your belt) to the top of your foot or your instep.
(broken image removed)
I followed the directions and measured for the top of my belt to my instep to get 39". I purchased the "XL = 40" length and they are a perfect fit.