Leather Thickness Converter
Convert between leather ounces (oz) and millimeters (mm) for leather thickness.
Includes iron number conversion and common leather uses.
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Leather thickness is measured differently depending on the country and trade. In the United States, leather thickness is traditionally measured in ounces (oz), while most other countries use millimeters (mm). The old British system uses irons.
Conversion formulas:
- 1 oz of leather = 1/64 inch = 0.3969 mm (approximately 0.4 mm)
- 1 iron = 1/42 inch = 0.6048 mm (approximately 0.6 mm)
- To convert oz to mm: mm = oz x 0.3969
- To convert mm to oz: oz = mm / 0.3969
- To convert irons to mm: mm = irons x 0.6048
Note about ounce measurements: Leather ounces refer to the weight of one square foot of leather at that thickness, not a volume measurement. A piece of leather that weighs 4 ounces per square foot is called “4 oz leather.”
Common leather thickness reference table:
| Oz | mm | Irons | Common Use |
|---|---|---|---|
| 1-2 oz | 0.4-0.8 | 0.7-1.3 | Garment lining, book covers |
| 2-3 oz | 0.8-1.2 | 1.3-2.0 | Wallets, handbag linings, gloves |
| 3-4 oz | 1.2-1.6 | 2.0-2.6 | Handbags, journal covers, moccasins |
| 4-5 oz | 1.6-2.0 | 2.6-3.3 | Bags, knife sheaths, light holsters |
| 5-6 oz | 2.0-2.4 | 3.3-4.0 | Belts (dress), saddlebags, cases |
| 6-7 oz | 2.4-2.8 | 4.0-4.6 | Belts (casual), light armor |
| 7-8 oz | 2.8-3.2 | 4.6-5.3 | Heavy belts, straps, holsters |
| 8-10 oz | 3.2-4.0 | 5.3-6.6 | Sole leather, heavy tooling |
| 10-14 oz | 4.0-5.6 | 6.6-9.3 | Shoe soles, heavy straps, armor |
Practical tips for leathercrafters:
- Most projects use leather in the 3-7 oz range, which covers wallets, bags, and belts.
- When buying leather, the ounce rating is often given as a range (e.g., 4-5 oz) because natural leather varies slightly in thickness across a single hide.
- Leather can be split or skived to reduce thickness for specific areas of a project, such as fold lines or edges.
- Vegetable-tanned leather is best for tooling and carving, while chrome-tanned leather is softer and better for garments.