Leather Sheet Thickness Converter
Convert leather thickness between ounces, millimeters, and irons. Standardize leather weight specs for tooling, stitching, and pattern layout projects.
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Inputs that matter
Thickness Value, From Unit
Output to expect
Leather Thickness Converter
How it works
1 documented formula across 1 calculation mode
- Confirm that every value uses the unit and time basis shown before comparing scenarios.
- Change one input at a time to see which assumption materially changes the result.
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Reference & details
How it works
Updated July 2026
How it works
Updated July 2026Ounces to Millimeters
Leather "ounce" weight refers to weight per square foot, which correlates to thickness. One ounce ≈ 0.4 mm in the standard conversion used by North American tanneries.
Thickness (mm) ≈ ounces × 0.4Irons to Millimeters
The iron (or ligne) is a traditional leathercraft unit. One iron equals 1/48 inch or approximately 0.529 mm, used widely in European leatherworking.
Thickness (mm) = irons × 0.529Cross-System Conversion
Convert between any two units by passing through millimeters as the common base. Round to practical fractions for skiving and machine settings.
oz ≈ mm / 0.4; irons ≈ mm / 0.529Updated: July 2026
Example Scenarios
4–5 oz ≈ 1.6–2.0 mm. Use 0.8–1.0 mm thread (Lin Cable 432 or Ritza 25) with 3.0–3.5 mm stitch holes for balanced hand stitching.
Pattern calls for 5 iron leather (~2.65 mm). Convert to 6–7 oz domestic equivalent when ordering from a US tannery listing ounce weight.
Clicker die rated for 3 mm max. A 9 oz strap at 3.6 mm exceeds capacity — split or skive, or select thinner stock before cutting.
Common Mistakes to Avoid
Common Mistakes to Avoid
Confusing iron (thickness unit) with pricking iron tool size
A "5 iron" thickness (2.65 mm) is unrelated to a "5 mm pitch pricking iron" spacing tool. Thickness irons measure hide depth; pricking irons set stitch hole spacing.
Assuming oz conversion is exact across all leather types
Dense latigo and loose-pull-up leather at the same oz can differ 0.2–0.3 mm. Caliper your actual hide at multiple points before precision fitting.
FAQ
Ounce weight is the weight of a 1 sq ft piece, not the actual scale weight of your cut. It correlates with thickness: 3 oz ≈ 1.2 mm, 8 oz ≈ 3.2 mm, 10 oz ≈ 4.0 mm.
Tanneries vary in compression, temper, and whether thickness is measured at crust or finished stage. Always caliper-measure critical pieces rather than relying on label oz alone.
One iron = 1/48 inch (0.529 mm). A 6-iron leather is about 3.17 mm. Irons appear in European patterns and pricking iron spacing references.
Divide mm by 0.4 for approximate oz. Example: 2.0 mm ≈ 5 oz. Order slightly heavier if you plan to skive — you cannot add thickness back.
Temper (soft, firm, boardy) affects stiffness and compressibility, not nominal thickness. A firm 5 oz skives differently than a soft 5 oz but measures the same calipered thickness.
About Leather Sheet Thickness Converter
Leather is sold and specified in ounces (oz), millimeters, or irons depending on region and trade. This converter translates between all three systems so you can match materials to patterns, machines, and thread recommendations.