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BIPM-ratified constants · v1.0

Converter

Shoe, size conversion calculator.

Convert shoe sizes between US Men's, US Women's, UK, EU, and centimeter systems using standard offset formulas and ISO Mondopoint measurements.

From

us

us_men

9 us_men =42Converted Shoe Size

Equivalents

Precision: 6 dp · Notation: Decimal · 5 units

Men

USus_men9

Women

USus_women10.5

Units

UKuk8.5
EUeu42

foot length

CMcm27

Common pairings

1 us_menequals2.5 us_women
1 us_menequals0.5 uk
1 us_menequals34 eu
1 us_womenequals-0.5 us_men
1 us_womenequals-1 uk
1 us_womenequals32.5 eu
1 ukequals1.5 us_men
1 ukequals3 us_women

The conversion

How the value
is computed.

How Shoe Size Conversion Works

Shoe sizing systems vary significantly across countries, making accurate shoe size conversion essential for international online shopping, travel, and footwear manufacturing. This calculator uses US Men's sizing as the canonical reference unit, applying linear offset formulas derived from industry-standard sizing charts to deliver consistent results across all major systems.

The Core Conversion Formulas

All conversions route through US Men's sizing as an intermediate value. The four primary relationships are:

  • UK Size: UK = USMen − 0.5
  • EU Size: EU = USMen + 33
  • Foot Length (CM): CM = 0.847 × USMen + 19.37
  • US Women's: USWomen = USMen + 1.5

These formulas reflect the linear relationship between US sizing increments and their international equivalents. Each full US size corresponds to approximately 8.47 mm of foot length, consistent with the barleycorn-based measurement system historically used in English-speaking countries, as documented by Shoe size — Wikipedia. The centimeter formula's slope (0.847) and intercept (19.37) are derived from regression modeling of standardized foot length data across US size increments.

Historical Context of Shoe Sizing Systems

The barleycorn unit, equal to 1/3 inch or approximately 8.47 mm, has served as the basis for English-speaking shoe sizing since the reign of King Edward II in the 14th century. This historical standard was formalized into modern sizing systems throughout the 20th century. The US adopted this incremental system, the UK maintains it with a consistent 0.5-size offset, and the EU developed its own system anchored to centimeter measurements. Understanding these historical roots explains why conversion offsets remain fixed constants rather than varying by size range—they represent fundamental differences in how each nation's standardization bodies defined and scaled their systems.

Step-by-Step Conversion Example

Consider a US Men's size 10 shoe. Applying each formula produces the following equivalents:

  • UK: 10 − 0.5 = 9.5
  • EU: 10 + 33 = 43
  • Foot Length: (0.847 × 10) + 19.37 = 8.47 + 19.37 = 27.84 cm
  • US Women's: 10 + 1.5 = 11.5

This single reference point illustrates how one US Men's size maps precisely across all major global systems without ambiguity.

Converting From Non-US Systems

When the source size is not US Men's, the calculator first converts to US Men's, then applies the target formula. For example, converting EU 42 to UK proceeds as: USMen = EU − 33 = 42 − 33 = 9, then UK = 9 − 0.5 = 8.5. For foot length in centimeters as the source, the inverse formula applies: USMen = (CM − 19.37) ÷ 0.847. A 27.0 cm foot yields USMen = (27.0 − 19.37) ÷ 0.847 ≈ 9.0, placing the wearer squarely in a US Men's 9.

Precision, Rounding, and Half-Sizes

Shoe sizes frequently include half-size increments (8.5, 9.5, etc.), particularly in US and UK markets, while EU sizing typically uses full increments. When converting between systems with different granularity, results may fall between standardized sizes. The calculator maintains decimal precision to one place, allowing users to identify intermediate sizes that best approximate their converted value. For centimeter-based measurements, this decimal representation provides exact foot length correspondence rather than requiring rounding to the nearest full size.

Methodology and Sources

The offset constants used in this calculator align with published sizing tables from the Brannock Device Sizing Instructions, the globally recognized standard for foot measurement since 1927. The Mondopoint system underlying the centimeter formula is codified in ISO 9407:2019 Footwear — Sizing — Mondopoint system, which defines shoe size in terms of mean foot length in millimeters, ensuring international comparability. Together, these two authoritative references anchor all conversion constants used here.

Limitations and Brand Variation

Shoe size conversion formulas provide standardized equivalents, but individual brands may apply proprietary lasts, adding up to half a size of variation. Always verify against a brand's published size chart when precision matters, particularly for athletic footwear, children's shoes, and specialty widths. The calculator assumes standard-width sizing (D for men, B for women) unless otherwise specified.

Practical Use Cases

  • Purchasing footwear from international retailers in UK, European, or Asian markets
  • Converting children's shoe sizes when traveling or shopping abroad
  • Verifying foot measurements for custom or orthopaedic footwear
  • Cross-referencing sizing between men's and women's lines of the same brand

Reference

Frequently asked questions

How do I convert US shoe size to EU size?
To convert a US Men's shoe size to EU, add 33 to the US Men's value. US Men's 9 equals EU 42, and US Men's 11 equals EU 44. For US Women's sizes, first subtract 1.5 to reach the US Men's equivalent, then add 33. A US Women's 9 becomes US Men's 7.5, which equals EU 40.5. The EU system increments by 6.67 mm per size unit.
What is the difference between US Men's and US Women's shoe sizes?
US Women's shoe sizes run 1.5 sizes larger than the equivalent US Men's size. A US Women's 8.5 corresponds to a US Men's 7.0, and a US Women's 11 corresponds to a US Men's 9.5. This offset reflects historical differences in last shapes between men's and women's footwear. Women shopping unisex or men's styles typically size down by 1.5 sizes to find the correct fit.
How do I convert shoe size to centimeters using foot length?
The formula for converting US Men's shoe size to centimeters is: CM = 0.847 × US_Men + 19.37. For a US Men's size 10, the calculation yields (0.847 × 10) + 19.37 = 27.84 cm. To convert a measured foot length back to US size, apply the inverse: US_Men = (CM − 19.37) ÷ 0.847. A 26 cm foot gives (26 − 19.37) ÷ 0.847 ≈ 7.8, which rounds to US Men's size 8.
How do I convert UK shoe size to US shoe size?
UK Men's sizes run 0.5 sizes smaller than US Men's sizes. To convert UK to US Men's, add 0.5 to the UK value. A UK 9 equals US Men's 9.5, and a UK 11 equals US Men's 11.5. For UK to US Women's, add 2.0 in total: UK 6 becomes US Women's 8. This offset has remained consistent since the adoption of the barleycorn sizing standard across English-speaking markets.
Are shoe size conversion formulas accurate across all brands?
The conversion formulas provide standardized equivalents based on industry references like the Brannock Device sizing system and ISO 9407:2019, but individual brands may deviate by up to half a size due to proprietary last designs and regional manufacturing preferences. Running shoes, luxury dress shoes, and children's footwear often show the most variation. Always cross-reference a specific brand's published size chart before purchasing, especially from international retailers where returns can be difficult.
What is the EU shoe size equivalent for a US Women's size 8?
A US Women's size 8 converts to EU 39.5. The calculation uses two steps: first, subtract 1.5 to reach the US Men's equivalent (8 − 1.5 = 6.5), then add 33 to get the EU size (6.5 + 33 = 39.5). This two-step process through the US Men's canonical unit ensures consistent and repeatable results across all supported sizing systems, including UK, EU, and centimeter-based Mondopoint measurements defined in ISO 9407:2019.