If crochet hooks are unmarked by the manufacturer, it is easy for a crocheter to forget which size a hook is. Knowing hook size is important for achieving the correct gauge in a crochet project, so crocheters can use a tool called a hook size gauge to ensure their hook is the correct size for a project at hand. There are two types of hook size gauges that will help find the size of a crochet hook: tapered hook size gauges and holed hook size gauges.
Using Tapered Hook Size Gauges to Find the Size of A Crochet Hook
Hold both the hook and the tapered hook size gauge in the air. Place the hook inside either the bigger or smaller tapered opening on the gauge, depending on the size of the hook.
Slide the hook down the tapered opening until it can no longer fit through the opening.
Trace across from the final fitting point in the opening to the measurement listed next to it. This is the size of the hook.
Using Holed Hook Size Gauges to Find the Size of A Crochet Hook
Hold the hook and hook size gauge in the air.
Stick the hook through one of the larger holes to see if it fits firmly. If the hole is too loose or too tight, try the other holes until a match is found.
Read the measurement under the smallest hole the hook will fit into. This is the hook's size.
While hooks are sometimes sized by their metric measurement, they often have a lettered or numbered size in the United States. For example, a 4mm hook is a size G/6 hook. Consult a conversion chart if the hook is marked with a letter/number size but no metric measurement.