Gauge is the number of stitches and rows in a set measure, usually 4 inches. It is the single most important factor in whether a project comes out the right size.
Make a swatch
Knit or crochet a swatch at least 4 inches square in the pattern stitch, then measure the stitches per inch. Compare it to the gauge the pattern lists.
Adjusting your gauge
Too many stitches per inch means go up a needle or hook size; too few means go down. Change the tool, not your natural tension, until the swatch matches.
See the Gauge Formula and the Knitting Gauge Calculator.
