sewcalcs.uk
Stitch Per Inch Calculator — SPI & Stitch Length
Calculate stitch length settings and stitches per inch conversions.
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
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.
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.
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.
Related Calculators
Fabric Cost Calculator
Calculate total fabric cost from meterage and price per metre.
Circle Skirt Calculator
Calculate radius, fabric and cutting layout for circle skirts.
Gored Skirt Calculator
Calculate gore panel dimensions for 4, 6, 8 or 12 gore skirts.
Yoke Calculator
Calculate yoke dimensions for skirts and bodices.
Flounce Calculator
Calculate inner and outer radii for circular flounces.
Was this calculator helpful?
Last updated: February 2026
All calculations are estimates. Always verify quantities before cutting or purchasing fabric.