Tutorial · Technique · First project
Swatching and gauge maths that actually predicts the finished size
Gauge is not a formality. A difference of two stitches per 10 cm turns a 100 cm chest into 110 cm, and no amount of careful knitting afterwards fixes it. This tutorial covers how to swatch so the number is real, and how to use it.
Published Abbreviation gauge
- Vknit
- -purl
At a glance
- Swatch sizeAt least 15 x 15 cm, measured over 10 cm in the middle
- BlockingWash and dry exactly as the finished object will be washed
- ToolsRuler, pins, a notebook
Working chart
| Step | Round / row | Stitches |
|---|---|---|
| Cast on enough stitches for 15 cm of fabric At 20 sts per 10 cm that is 30 stitches plus 4 edge stitches. | - | 30 |
| Work in the stitch pattern the project uses Cables and colourwork must be swatched as cables and colourwork. | 1-40 | 30 |
| Bind off and wash exactly as the garment will be washed Cool water, wool wash, no agitation. Acrylic needs three washes. | - | - |
| Dry flat and let it rest for at least two hours Wool relaxes as it dries; measuring wet overstates the gauge. | - | - |
| Measure 10 cm in the middle, in three places Use a hard ruler laid flat, not a tape measure held in the air. | - | 20 |
Measurements
| Target gauge | Your swatch | Stitches for a 100 cm chest |
|---|---|---|
| 20 sts / 10 cm | 20 sts | 200 |
| 20 sts / 10 cm | 19 sts | 190 |
| 20 sts / 10 cm | 21 sts | 210 |
| 20 sts / 10 cm | 22 sts | 220 |
Yarn and yardage
| Gauge difference | Width error on a 100 cm chest | Yarn difference |
|---|---|---|
| 1 st per 10 cm | 5 cm | 5% |
| 2 sts per 10 cm | 10 cm | 10% |
| 3 sts per 10 cm | 15 cm | 15% |
| 4 sts per 10 cm | 20 cm | 20% |
Why a 10 x 10 cm swatch is not enough
A 10 x 10 cm swatch is mostly edge. The stitches at the sides are pulled by the cast-on and bind-off and do not behave like stitches in the middle of a garment, so measuring the whole swatch measures the edges too.
Work at least 15 x 15 cm and measure 10 cm in the middle. The extra yarn costs about 15 metres. The measurement error it removes is worth several centimetres of finished garment.
Wash and block before measuring
Wool, alpaca and cotton all change size in the first wash. Non-superwash wool typically relaxes and the stitches open up by 3-5%; cotton can shrink 2%; superwash wool grows 2-4% and then holds. Measuring off the needles measures a fabric that will not exist after the first wash.
Wash the swatch the way the finished garment will be washed - same temperature, same detergent, same machine or hand - and dry it flat. If the garment will be hung to dry, the swatch should be hung too, because hanging changes the row gauge.
The arithmetic
Divide the stitch count by the width in centimetres and multiply by ten. A swatch measuring 21 stitches over 10 cm means 2.1 stitches per centimetre. For a finished chest of 100 cm plus 2 cm of ease, cast on 2.1 x 102 = 214 stitches, rounded to 216 so it divides by four for ribbing.
Work the same calculation for rows: 28 rows over 10 cm is 2.8 rows per centimetre, so a 40 cm body needs 112 rows. Row gauge matters less on a garment measured in centimetres, and more on anything shaped by row count, like a raglan yoke.
When your gauge is off
Too many stitches per 10 cm means your fabric is too tight: go up a needle size. Too few means too loose: go down. Change one size at a time and re-swatch, because the relationship between needle size and gauge is not linear - a half-millimetre change usually moves gauge by 5-8%.
What to do if it never matches
If two needle sizes bracket the target and neither hits it, change the size you are knitting rather than the needle. Work the stitch count for the size your gauge produces: if your gauge is 22 stitches per 10 cm against a pattern's 20, knit the size whose finished chest is 9% smaller than the one you wanted.
That is the reason garment patterns are written with the gauge stated first. Everything else in the pattern is arithmetic on top of it, and only the gauge is measured rather than calculated.