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Stitches per inch by leather weight
Stitches per inch (SPI) is set by your stitching irons or pricking irons, and it's one of the biggest drivers of how hand-stitched leather looks. The rule that ties it together: the heavier the leather and the larger the item, the lower the SPI; the thinner the leather and the finer the goods, the higher the SPI. A stitch that looks crisp on a card wallet looks toy-like on a belt.
SPI by leather weight and project
Leather thickness is measured in ounces (1 oz ≈ 1/64 inch). A practical starting guide:
| Project | Leather weight | Typical SPI |
|---|---|---|
| Wallets, card holders, fine goods | 2–4 oz | 7–9 |
| Bags, watch straps, medium goods | 4–7 oz | 6–7 |
| Belts, sheaths, heavy goods | 8–12 oz | 4–6 |
SPI to millimeters
Irons are often sold by spacing in millimeters, so it helps to convert (spacing = 25.4 ÷ SPI):
| SPI | Spacing |
|---|---|
| 9 | ~2.8 mm |
| 8 | ~3.2 mm |
| 7 | ~3.6 mm |
| 6 | ~4.2 mm |
| 5 | ~5.1 mm |
Proportion is the real goal. SPI isn't about strength so much as looking right for the piece. Thicker thread suits lower SPI and heavier leather; fine thread suits higher SPI. Match thread thickness, iron spacing, and leather weight as a set.
Packing many small holes close together in heavy leather perforates it like a stamp — the stitch line can tear. Lower SPI on thick leather isn't just aesthetic; it leaves enough material between holes.
Hide picks SPI for your project
Choose your leather weight and project and Hide suggests an SPI (and iron spacing), then sizes thread, edge, and finishing to match — with brand-aware presets. Free to download.
Sources
- Al Stohlman, The Art of Hand Sewing Leather; Nigel Armitage stitching tutorials
- Practitioner guidance on iron spacing and thread sizing (e.g. Stitchpunk, Corter Leather)
Weights and SPI are starting points — match thread, iron, and leather as a set for your piece.