The easiest way to measure foot size is to trace the shape of the foot while standing on a large piece of paper. Measure the width and length of the tracing using a ruler or tape measure. The length of the foot dictates the shoe size.
To convert between length of foot in inches and commercial shoe size, consult a chart provided by the shoe manufacturer. The width of the foot dictates whether a special width of shoe – usually indicated by a letter after the numerical size – is needed. Average-sized feet take an average width. Each shoe manufacturer uses a different system to denote shoe width.