XS: Size 75 strap measures 29" from tip to middle hole.  25-30" Fit = 75 (XS)

S: Size 80 strap measures 31" from tip to middle hole.  27-32"Fit = 80 (S)

M: Size 85 strap measures 33" from tip to middle hole.  29-34" Fit = 85 (M)

L: Size 90 strap measures 35" from tip to middle hole.  31-36" Fit = 90 (L)

XL: Size 95 strap measures 37" from tip to middle hole.   33-38" Fit = 95 (XL)