Gauge calculator
Crochet a 15 × 15 cm swatch in the pattern stitch, then measure 10 cm (4 in) across the middle and count your stitches.
Check your gauge
Compare your swatch with the pattern's gauge (both counted over the same 10 cm / 4 in).
How many stitches to start?
Use your gauge (from the swatch above) to work out a starting stitch count for any width.
Add any turning or foundation chains your pattern calls for on top of this.