A US size 8 is not a UK size 8. It’s a UK 12. This single fact causes more wrong-size orders between American and British shoppers than any other piece of clothing math — and unlike a lot of sizing confusion, it has an exact, reliable formula behind it.
This guide gives you that formula, a full conversion chart in inches and centimetres, and — more usefully — the specific situations where the formula stops being reliable and you need to check the brand’s own chart instead.
Key Takeaways
- The core rule: US size + 4 = UK size, for women’s tops, dresses, skirts and most ready-to-wear. A US 8 is a UK 12.
- For EU sizes: US size + 32 = EU size. A US 8 is an EU 40.
- Shoes use a different formula entirely — do not apply the clothing rule to footwear.
- Letter sizes (XS–XL) are usually identical between the US and UK, but the underlying numeric sizes and measurements behind each letter are not.
- The formula holds for maybe 70–80% of mainstream brands. Fast fashion and designer labels are the two categories most likely to break it.
- When the size number and your actual measurements disagree, trust the measurements.
US to UK/EU Size Calculator
Enter a US size to convert. Clothing and shoes use different formulas, so pick the right tab.
These are standard conversions. Always check the brand’s own size chart before buying.
The Core Rule for Women’s Clothing
US size + 4 = UK size. A US 4 is a UK 8. A US 8 is a UK 12. A US 12 is a UK 16.
US size + 32 = EU size. A US 8 is an EU 40. A US 6 is an EU 38.
This rule applies to tops, dresses, blouses, skirts, jumpsuits and most standard women’s ready-to-wear. It does not apply to shoes, kidswear, or most men’s clothing, which each use their own separate systems — more on those below.
| US | UK | EU | Bust (in / cm) | Waist (in / cm) | Hip (in / cm) |
|---|---|---|---|---|---|
| 0 | 4 | 32 | 31–32 / 79–81 | 24–25 / 61–64 | 34–35 / 86–89 |
| 2 | 6 | 34 | 32–33 / 81–84 | 25–26 / 64–66 | 35–36 / 89–91 |
| 4 | 8 | 36 | 33–34 / 84–86 | 26–27 / 66–69 | 36–37 / 91–94 |
| 6 | 10 | 38 | 34–35 / 86–89 | 27–28 / 69–71 | 37–38 / 94–97 |
| 8 | 12 | 40 | 35–36 / 89–91 | 28–29 / 71–74 | 38–39 / 97–99 |
| 10 | 14 | 42 | 36.5–37.5 / 93–95 | 29.5–30.5 / 75–77 | 39.5–40.5 / 100–103 |
| 12 | 16 | 44 | 38–39 / 97–99 | 31–32 / 79–81 | 41–42 / 104–107 |
| 14 | 18 | 46 | 40–41 / 102–104 | 33–34 / 84–86 | 43–44 / 109–112 |
These figures follow the general EN 13402 standard used across most of Europe and adopted loosely by many UK and US size charts. Treat the measurement columns as more reliable than the size numbers — a size label is a marketing decision as much as a measurement, and that’s exactly the problem the next section covers.
Why the Same Body Gets a Different Number in Each Country
The four-number gap between US and UK sizing isn’t an accident or a rounding difference. It comes from two separate things.
Different baseline standards. UK and most EU sizing loosely follows the EN 13402 standard, which ties a size number to a specific measurement range. The US never adopted a single mandatory standard in the same way, so US sizing has always had more room to drift.
Vanity sizing. Since the 1980s, many US brands have gradually resized their labels so that the same body measurements get a smaller number over time — a size 8 today often fits what would have been labelled a size 12 decades ago. This happened because a smaller number sells better. The UK market saw a milder version of the same drift, but not to the same degree, which is a large part of why the US-to-UK gap isn’t a clean, fixed number across every brand.
Shoes Use a Completely Different System
This is the most common mistake people carry over from clothing sizing. Shoe sizes do not follow the US+4 rule at all.
| US Women’s | UK | EU | Foot Length (in / cm) |
|---|---|---|---|
| 5 | 3 | 35–36 | 8.5 / 21.6 |
| 6 | 4 | 36–37 | 8.75 / 22.2 |
| 7 | 5 | 37–38 | 9.1 / 23.1 |
| 8 | 6 | 38–39 | 9.4 / 23.9 |
| 9 | 7 | 39–40 | 9.75 / 24.8 |
| 10 | 8 | 40–41 | 10.1 / 25.6 |
The rough shortcut here is US size − 2 = UK size for women’s shoes — the opposite direction from the clothing rule, and a different gap entirely. If you only remember one thing from this section, remember that: clothing adds, shoes subtract, and they’re not the same number.
Foot length in cm or inches is the more reliable figure if you have it, since shoe fit varies by brand more than most clothing categories.
When the Formula Breaks: Brand Exceptions
The +4 rule is a genuinely useful starting point, but it’s a generalisation, not a guarantee. Two categories break it most often.
Fast fashion. Brands with fast production cycles and frequent size-range changes tend to drift furthest from the standard formula, and drift inconsistently between garment types within the same brand — a dress and a pair of trousers from the same label may not follow the same conversion.
Designer and premium labels. These often run smaller than the standard chart, sometimes significantly, because their target sizing skews toward a narrower range. Each brand manages its own sizing internally before it ever reaches the customer, which is exactly why the standard chart works as a starting point rather than a guarantee.
The practical response to both: use this chart to get your starting size, then check that specific brand’s own size guide before ordering, and lean on your actual bust/waist/hip measurements over the label number whenever they disagree.
Men’s and Kids’ Clothing: Different Rules Again
Men’s clothing has the smallest US-UK gap of any category. Most men’s tops and jackets use identical or near-identical numbers between the US and UK — a size 40 jacket is a 40 in both markets, since both are commonly based directly on chest measurement in inches. Letter sizes (S, M, L, XL) are also generally identical.
Kids’ clothing is sized by age or height rather than a numeric scale in both countries, but the age bands themselves don’t always line up exactly, since they’re built around each country’s average growth curves. When ordering for a child close to a size boundary, height in cm is more reliable than the age label.
A Faster Way to Check Before You Buy
- Find your US size on the chart above and read across to the UK/EU column
- Check that specific brand’s own size chart — search “[brand name] size chart” if it’s not on the product page
- Compare your actual bust, waist and hip measurements against the brand’s measurement chart, not just the size number
- For shoes, use foot length in cm if the brand provides it, rather than converting the size number
- If you’re between two sizes, size up for structured garments (blazers, coats) and consider sizing down for stretch fabrics
Getting the size right matters, but so does keeping the garment in shape afterwards — see our guide on how to stop black jeans from fading.
Frequently Asked Questions
Is a US 8 the same as a UK 12?
Yes, under the standard conversion. A US size 8 is a UK size 12 and an EU size 40, following the US+4=UK and US+32=EU rules for women’s clothing. Always check the specific brand’s chart, since not every label follows this exactly.
Do UK sizes run bigger or smaller than US sizes?
UK sizes use a bigger number for the same body — a UK 12 and a US 8 fit the same measurements. So “bigger number” does not mean “bigger garment” here; it just reflects a different numbering scale.
Are UK and US shoe sizes calculated the same way as clothing?
No. Clothing sizes add roughly 4 going from US to UK. Shoe sizes subtract roughly 2. These are separate systems and mixing them up is the most common conversion mistake.
Why do two UK size 12s from different brands fit differently?
Because size labels are a brand decision as much as a measurement standard. Fast fashion and designer labels are the two categories most likely to deviate from the standard chart, sometimes by a full size or more.
Should I trust the size chart or my own measurements more?
Your own measurements, whenever they disagree with a size label. The label is the brand’s interpretation of a size; your bust, waist and hip measurements in inches or cm are the actual reference point the chart is built from.
Do men’s sizes need converting between the US and UK?
Rarely. Most men’s clothing uses the same or near-identical numbers in both countries, since sizing is commonly based directly on chest measurement in inches rather than a separate scale.
The Short Version
For women’s clothing: add 4 to go from US to UK, add 32 to go from US to EU. For shoes: subtract roughly 2 going from US to UK — a different direction and a different number entirely. Use the chart to get your starting point, then check the specific brand before you buy, because the formula is a strong starting rule, not a guarantee.
