What stitch length should I use?

Standard sewing: 2.5mm (10 SPI). Topstitching: 3-3.5mm (7-8 SPI). Basting: 5-6mm (4-5 SPI). Gathering: 4-5mm. Fine fabrics: 1.5-2mm (12-16 SPI). Adjust based on fabric weight and thread.

SPI means Stitches Per Inch. It is the number of stitches in one inch (2.54cm) of sewing. Higher SPI means shorter, closer stitches. UK and many modern machines use millimetre stitch length settings instead.

How do I convert SPI to millimetres?

Divide 25.4 (millimetres per inch) by the SPI value. For example, 10 SPI = 25.4 / 10 = 2.54mm stitch length. This calculator does the conversion automatically.

How do I check my stitch length?

Sew a line of stitches on fabric. Measure 2.5cm (1 inch) of stitching and count the stitches. This is your SPI. Or measure the distance between 10 stitches and divide by 10 for average stitch length in mm.

SewCalcs

Stitch Per Inch Calculator — SPI & Stitch Length

Calculate stitch length settings and stitches per inch conversions.

Convert From

Stitches Per Inch (SPI)

How We Calculate This

Stitch length and SPI are inversely related. Converting between them uses the factor 25.4 (millimetres per inch).

The formula

Stitch length (mm) = 25.4 ÷ SPI

SPI = 25.4 ÷ Stitch length (mm)

Stitches per cm = SPI ÷ 2.54

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before cutting or purchasing fabric.