How US and UK Shoe Sizes Differ
Shoe sizes represent foot length and width, but each country measures these dimensions using its own formula and unit system. The US and UK both derive their sizing from foot length in inches, yet apply different mathematical conversions, which explains why a US 10 men's shoe is not the same as a UK 10.
In the United States, sizing formulas are:
- Men: US size = (3 × foot length in inches) − 22
- Women: US size = (3 × foot length in inches) − 21
- Children: US size = (3 × foot length in inches) − 9.67
In the United Kingdom, the formulas shift by one or more full sizes:
- Adults: UK size = (3 × foot length in inches) − 23
- Children: UK size = (3 × foot length in inches) − 10
This offset means men's sizes are consistently 1 full size smaller in the US than the UK, while women's US sizes are 2 sizes smaller than their UK counterparts.
Converting Between US and UK Sizes
The conversion relies on foot length as the common reference point. If you know your foot length in millimetres or inches, you can calculate any regional size standard. Alternatively, use the direct conversion shortcuts when you already have a size in one system.
UK size = (3 × foot_length_mm) − 23
US men's = (3 × foot_length_mm) − 22
US women's = (3 × foot_length_mm) − 21
UK child = (3 × foot_length_mm) − 10
US child = (3 × foot_length_mm) − 9.67
Direct conversion (no foot measurement):
US men's size = UK size − 1
US women's size = UK size − 2
foot_length_mm— Your foot length measured from heel to longest toe, in millimetresfoot_length_inch— Your foot length converted to inches (divide mm by 25.4)UK size— Your shoe size in the United Kingdom sizing systemUS men's— US shoe size for menUS women's— US shoe size for women
Measuring Your Foot for Accurate Conversion
The most reliable conversions start with an accurate foot measurement. Shoes are fitted based on foot length, not just aesthetic preference, so a precise baseline prevents missteps.
How to measure:
- Stand barefoot on a flat surface with your heel against a wall or straight edge.
- Place a ruler or measuring tape along the floor, aligned with your heel.
- Mark the point where your longest toe ends (usually the big toe, though some people have a longer second toe).
- Record the distance in millimetres or inches.
- Repeat on both feet and use the longer measurement—sizes accommodate your larger foot.
Avoid measuring while sitting, as your foot expands slightly under body weight. If you swell throughout the day (common in warm climates or during pregnancy), measure in the evening when swelling is greatest. Always measure in the shoes and socks you'll actually wear.
Beyond US and UK: European, Japanese, and Korean Sizes
The global shoe market operates on at least six major sizing standards. Once you know your foot length, converting to European, Japanese, Mexican, or Korean sizes is straightforward.
The EU standard applies across most of Europe and is the most widely available alternative online. EU sizes are typically 30–35 points larger than UK sizes. Japanese and Mexican shoe sizes match foot length in centimetres, making them the easiest to understand—a size 25 in Japan literally means a 25 cm foot. Korean sizes multiply foot length in inches by 25.4, effectively showing foot length in millimetres.
Our calculator automatically displays conversions to EU, Japanese, Mexican, and Korean standards alongside your US and UK results, so you have every size reference at a glance when shopping internationally.
Common Conversion Pitfalls
Even with the right size number, fit depends on brand, width, and material stretch. Watch for these traps:
- Men's and women's sizes are offset differently — Men's US shoes are 1 size smaller than UK; women's are 2 sizes smaller. Using the male formula for a women's shoe (or vice versa) guarantees a poor fit. Always check whether the shoe is branded for men or women before converting.
- Child sizes shift at certain age thresholds — Children's shoe sizing ends around UK 13.5, after which sizing jumps to adult scales. A child wearing adult-sized shoes should be measured and converted using adult formulas, not child formulas, or you'll order something vastly too large.
- Foot length varies by time of day and season — Feet swell in heat, during pregnancy, and after long periods of standing or walking. Measure in the evening, in the season you'll wear the shoes most, and account for the socks you actually wear. A 2 mm difference in measurement can shift your size by a half-size.
- Width and shoe lasts aren't standardised across regions — UK and US use different width codes (UK: B, C, D, E, EE; US: AA, A, B, D, E, EEEE). A UK 6D may fit differently than a US 7D even though both claim to be wide. Always check width separately and read reviews from people with similar foot shapes.