Check your gauge against a pattern, and work out exactly how many stitches to chain.
Gauge is the number of stitches and rows in a set measurement — usually 10cm (4in) — and it's the single biggest reason two people can crochet the "same" pattern in completely different finished sizes. If your gauge is tighter than the pattern's (more stitches per 10cm), size up your hook. If it's looser (fewer stitches), size down. Re-check your swatch after each hook change.
Why does crochet gauge matter?
Gauge determines the finished size of your project. If your stitch count per 10cm doesn't match the pattern's gauge, your finished piece will come out smaller or larger than intended — critical for garments and fitted items.
What do I do if my gauge doesn't match the pattern?
If you have more stitches per 10cm than the pattern, switch to a larger hook. If you have fewer, switch to a smaller hook. Re-swatch after changing hook size and check again before starting the project.
How big should a gauge swatch be?
Crochet a swatch at least 12–15cm square so you can measure a clean 10cm section away from the curled edges, which distort stitch size. Block the swatch the same way you plan to block the finished piece before measuring.