Saddle Stitch Thread Calculator
Thread to cut for a hand saddle stitch in leather, from seam, thickness and stitch spacing.
Result
Thread to cut: 42.8 inEstimate
One length, a needle at each endThe geometry runs a little long; a thread that is too short needs a join in the seam.
- Stitches
- 66
- Holes
- 67
- Stitch length
- 3.85 mm (0.15 in)
- Thread as a multiple of the seam
- 4.28Estimate
https://calcgallery.com/crafts/saddle-stitch-thread-calculator/
Results are arithmetic on the figures you enter and are estimates. Products, materials and animals vary, so follow the maker's instructions and label, make a test piece where it matters, and ask a vet about feeding. Nothing here is safety or veterinary advice. Read the full disclaimer
How to use the Saddle Stitch Thread Calculator
- Measure the seam from the first hole to the last.
- Enter the total thickness the thread goes through, all layers together.
- Enter the hole spacing from your pricking iron or chisel, or the stitches per inch.
- Add any backstitches and the extra for tails, then read the thread to cut.
How it is calculated
spacing = hole spacing, or 1 in ÷ stitches per inchstitches = ⌈seam ÷ spacing⌉ holes = stitches + 1thread = 2 × stitches × spacing the two faces + 2 × holes × thickness both needles through every hole + 4 × backstitches × (spacing + thickness) + tailsA saddle stitch uses one thread with a needle at each end. Both needles pass through every hole from opposite sides, so each face carries a line of stitches and each hole carries the thread twice. That is the whole of the geometry; the tails are what you hold and tie off.
Why it runs a little long
The page assumes the thread goes straight through the full thickness. In practice the leather compresses as each stitch is pulled tight, and the forum rules of thumb, about four times the seam plus a few inches, come in a little shorter on thick work. Leather Beast’s rule is four times the seam plus 3 to 6 inches. A thread slightly too long is trimmed; one too short needs a join partway along the seam, which is weaker and shows.
Long seams
Long threads tangle and wear as they are pulled through again and again, so many makers cut no more than an arm span at a time and join a new thread at a hole. Divide the total by the length you like to work with to see how many threads to cut. For a belt, the belt blank calculator gives the strap length to stitch.
With your numbers
- Stitches = ⌈10 in ÷ 3.85 mm⌉ = 66, holes 67
- Faces = 2 × 66 × 3.85 mm = 20 in; through the holes = 2 × 67 × 3.18 mm = 16.8 in
- Thread = 20 in + 16.8 in + 0 in + 6 in = 42.8 in
Quick reference
The geometry runs a little long; a thread that is too short needs a join in the seam.
| Example | Thread to cut |
|---|---|
| 10 in seam, 1/8 in, 3.85 mm | 42.8 in |
| 10 in seam, 1/4 in, 3.85 mm | 59.5 in |
| 12 in seam, 1/4 in, 6 SPI, 2 back | 71.8 in |
| 8 in seam, 3/16 in, 8 SPI | 46.4 in |
| 25 cm seam, 4 mm, 4 mm spacing | 116.6 cm |
| 30 cm seam, 3 mm, 3.38 mm, 3 back | 141.8 cm |
Common questions about the Saddle Stitch Thread Calculator
- How much thread do I need for a saddle stitch?
- More than most people expect: the thread lies on both faces of the leather and passes through every hole twice, once from each needle. For a 10 inch seam through 1/8 inch of leather at 3.85 mm spacing that is about 43 inches of thread including 6 inches of tails, a little over four times the seam.
- Is four times the seam length a good rule?
- It is a common one, and it works for thinner leather at ordinary spacing. It falls short on thick stacks and on close stitching, because the part that passes through the holes grows with both. This page counts that part directly, so the multiple it shows changes with your leather and spacing.
- Why does closer stitching use more thread?
- The thread along the faces is about twice the seam whatever the spacing, but every extra hole adds two more trips through the leather. At 8 stitches per inch through 1/4 inch of leather, the trips through the holes use more thread than the faces do.
- How do I convert stitches per inch to millimetres?
- Divide 25.4 by the stitches per inch. Six stitches per inch is a spacing of about 4.2 mm, and a 3.85 mm iron gives about 6.6 stitches per inch. Choose whichever your tool is marked in.