Stitch length converter
Convert a pattern’s stitches per inch to your machine’s stitch length in mm, or back.
That's 1.02× as long as a standard seam, while topstitching on jeans is 1.38× longer.
What it means
How long is that stitch?
For straight stitch. Thread tension and fabric thickness change the stitch you actually get by a little.
Every unit
That stitch in every unit
Learn
Three things worth knowing
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25 ÷ SPI
Divide about 25 by the SPI for mm: 8 SPI ≈ 3.2 mm, 12 SPI ≈ 2.1 mm.
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Singer’s dial
Early sewing machines marked stitch length in stitches per inch; European makers switched the dials to millimeters in the 20th century.
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More SPI, shorter stitch
A higher SPI means shorter stitches, not longer.
Shortcuts
Popular stitch conversions
Background
About stitch length
Modern machines set the stitch length in millimeters; older machines, US patterns and leatherwork use stitches per inch. They are inverses: 25.4 ÷ SPI = mm. The everyday default, 2.5 mm, is 10 SPI.