Wrench and Socket Size Chart

Wrench and socket sizes describe the distance across the flats of a bolt head or nut, not the bolt's thread diameter. This chart lists standard imperial wrench sizes with their decimal inch value and the closest metric socket size, useful when you only have one tool set on hand and need to know how close a substitute will fit.

The metric column is an approximate cross reference, not an exact match. A metric socket one size off an imperial bolt head can feel like it fits, but a loose fit rounds off bolt heads over repeated use, so match the exact size whenever one is available.

A bolt's head size does not always match its thread diameter directly. A 1/4-20 bolt, for example, commonly takes a 7/16" wrench, not a 1/4" one. When in doubt, measure the head across the flats with a caliper and match the decimal reading to this chart, or to the bolt size chart for the thread specification underneath.

A set covering 1/4" through 3/4" in imperial, or 6 mm through 19 mm in metric, handles the overwhelming majority of household, furniture, and small engine hardware. Add larger sizes only as a specific job requires them.