Stitchbay guide
Knitting gauge calculator: stitches per 10 cm (4 in) from your swatch
Gauge (tension in UK patterns) is how many stitches and rows fit in 10 cm, or 4 inches. Measure a flat part of your swatch away from the edges, count the stitches across it, and the calculator scales that to 10 cm. If yours is more than the pattern's, your stitches are smaller: go up a needle size.
Gauge from your swatch
Knit a proper swatch
Cast on at least 10 cm worth of stitches plus a few for a border, in the stitch the pattern's gauge is given in, and knit until it is square. Wash and dry it the way you will treat the finished piece: many yarns grow or shrink. Then measure in the middle.
Too many or too few
More stitches than the pattern in 10 cm means your work is tighter and the piece will come out smaller: try needles half a millimetre bigger. Fewer stitches means it is looser: go down. Row gauge matters most where the pattern counts rows, like a raglan yoke.
What a count will measure
Put any stitch count in the second box to see how wide it will be at your gauge: handy to check a pattern's cast-on before you start.
Questions
Is gauge the same as tension?
Yes: UK patterns say tension, US patterns say gauge.
Does gauge matter for scarves and blankets?
Less: they don't need to fit, though a looser gauge uses more yarn. For hats, socks and jumpers it decides whether they fit.