Leather Thickness Converter

No. An ounce is 1/64 inch (about 0.397 mm) and an iron is 1/48 inch (about 0.529 mm), so one ounce is exactly 0.75 iron and one iron is about 1.33 ounces. The ounce is the US tannery scale; the iron is the older British gauge still used for shoe and sole leather. This calculator converts each against its own exact inch fraction.

The calculator first converts your Thickness Value to millimeters based on whichever unit you selected, then recalculates ounces, irons, and inches from that millimeter figure. Switching the Input Unit changes what your entered number is assumed to mean, which changes every converted value that follows from it -- and since an ounce and an iron are different sizes, switching between Ounces and Irons changes the numbers too, not just Millimeters and Inches.

Weight Class translates the millimeter thickness into the rough categories leatherworkers use when choosing material -- Garment leather for thin, drapey pieces like clothing, up through Extra Heavy for structural items like belts and holsters. It's a quick sanity check on whether a thickness suits your project type.

The 1/64-inch (about 0.397 mm) per-ounce figure is exact by definition, but actual hide thickness varies by tannery, hide section, and how the leather was split or finished, so a supplier's stated ounce weight is itself an approximation of the real hide. Treat the converted values as a close estimate for planning purposes, not a guaranteed measurement of any specific piece of leather.