Calculate perfect-bind spine thickness from interior page count and actual paper caliper, plus the flat cover size with bleed.
Result
Interior Leaves 50
Spine Width 0.200 in
Spine Width (mm) 5.08 mm
Flat Cover Size 12.200 × 9.000 in
Cover Size + Bleed 12.450 × 9.250 in
Formula: spine width = (interior pages ÷ 2) × actual paper caliper + adjustment. Use the actual caliper for the specific paper whenever possible; thickness can vary by stock and manufacturer.