Measure heel-to-toe foot length and see what a simplified shoe-size formula can—and cannot—tell you. The animation explains unit conversion, sizing offsets and brand-specific fit.
Open the shoe size calculator inches to shoe size · More Miscellaneous videos
The calculation
A simplified adult US estimate uses 3 × length in inches − an offset; use a matching brand chart for fit
Worked example
A 10-inch measurement equals 25.4 cm. In the simplified adult US estimates illustrated here, 3 × 10 − 22 gives a men’s estimate of 8, while 3 × 10 − 21 gives a women’s estimate of 9. Those arithmetic examples do not establish a universal size.
Measure both feet using the chosen brand’s instructions. Use that brand’s foot-length chart and consider width and fit; the centimeter label on a shoe box may not represent measured foot length.
Video chapters
- 0:00 — Is a 10-inch foot always the same size?
- 0:16 — Measure heel to longest toe
- 0:33 — Keep the input unit consistent
- 0:50 — An illustrative adult US estimate
- 1:08 — The system changes the offset
- 1:29 — Rounding does not create an exact fit
- 1:44 — Use the matching manufacturer chart
- 2:01 — Measure, match the system, check the chart
Read the full transcript
A foot measures ten inches from heel to longest toe. What shoe size is that? You need more than a length: the sizing system and the manufacturer's chart matter. A simple formula can illustrate the arithmetic, but it cannot guarantee how a shoe fits.
Measure the actual foot, not the outside of an old shoe. Stand with weight on the foot, mark the heel and longest toe, and measure between them. Check both feet. Follow the chosen brand's measuring instructions, including how it handles a difference between the two feet.
If a formula expects inches, convert centimeters first. Ten inches equals twenty-five point four centimeters. Centimeters divided by two point five four gives inches. Mixing a centimeter measurement with an inch-based formula gives a number with the wrong meaning.
One simplified adult U S men's estimate multiplies foot length in inches by three, then subtracts twenty-two. With ten inches, three times ten is thirty, and thirty minus twenty-two is eight. Treat that as an approximate formula result, not a universal fitting recommendation.
Using a different offset changes the size label without changing the foot. A simplified U S women's formula subtracts twenty-one instead, so the same arithmetic example gives nine. Those equations are educational approximations. Do not assume every brand uses a one-size difference between its men's and women's ranges.
Suppose a formula gives eight point three. Rounding to a half-size might suggest eight and a half, but that only rounds a number. Width, toe shape, and the shoe's construction still matter. Never confuse a decimal result with precision about comfort.
For an actual selection, compare your measurement with the brand's chart for that product and sizing range. Read whether the chart describes foot length or another label measurement. Nike, for example, distinguishes foot length from the centimeter size printed on its boxes. Follow the chart's own guidance between sizes.
Measure both feet consistently, convert units when needed, and identify the sizing system before doing the arithmetic. A formula gives an estimate; a matching manufacturer chart and a fit check make the answer useful. The length stays the same even when the size label changes.