The quick answer: Measure your bare foot in millimeters, then convert once. US women's sizes run about 1.5 sizes larger than US men's — a 250 mm foot is roughly a US women's 8.5 and a US men's 7. Unisex shoes are almost always labeled in men's numbers, so Oscar Blackwood shoppers should subtract 1.5 from their women's size.
Shoe sizing is not one system — it's four systems arguing with each other on the same product page. US women's, US men's, UK and EU numbers were built on different scales, and "unisex" isn't a fifth scale at all: it's men's sizing with a friendlier name. The one thing all four agree on is your foot length in millimeters. Start there, and every other number becomes arithmetic.
How do you measure your foot length in millimeters at home?
Trace both feet on paper at the end of the day, then measure heel to longest toe in millimeters — that number is your true size input. Feet swell up to 4% over a day, so a morning measurement will run small on the shoes you actually wear at 6 p.m.
- Tape a sheet of paper to a hard floor against a wall.
- Stand with your heel touching the wall, weight fully on the foot being traced. Sitting down shortens the reading by several millimeters.
- Mark the tip of your longest toe — for roughly one in five people that's the second toe, not the big toe.
- Measure from the wall edge of the paper to the mark in millimeters. Repeat for the other foot.
- Record both numbers separately. Do not average them.
Do not add "growing room" to the measurement. Standard size charts already build in 8–12 mm of toe spring, so padding your number is how people end up in shoes a full size too long that slip at the heel. If you land exactly between two rows on the chart, go up — a slightly long shoe can be fixed with a heel grip, a short one cannot be fixed at all.
What is the women's to men's shoe size conversion?
Subtract 1.5 to go from US women's to US men's, and add 1.5 to go the other way. A US women's 9 is a US men's 7.5; a US men's 10 is a US women's 11.5. That 1.5 gap is fixed across the adult range and does not drift at the extremes.
The catch is that length is only half the fit. Women's lasts are typically cut narrower through the heel and forefoot and have a shallower instep, so a converted men's shoe in the correct length can still feel roomy at the heel — and a converted women's shoe can feel tight across the ball of the foot even when the length is perfect. Width codes are not interchangeable either: a men's D is a standard men's width, but roughly equivalent to a women's wide.
As fashion stylists often note, the size number gets you into the right neighborhood — the last shape decides whether you actually live there comfortably.
This matters commercially, not just anatomically. The National Retail Federation reported that Americans returned about 14.5% of everything they bought in 2023 — roughly $743 billion in merchandise, with apparel and footwear among the worst-performing categories. Nearly all of that is fit, and most of the footwear share is one careless conversion.
What does your foot length in mm equal in US, UK, EU and unisex sizes?
Find your millimeter measurement in the left column and read across — the unisex column is identical to US men's, because that's how unisex shoes are labeled. EU numbers are the loosest of the four and vary by up to a full size between brands, so treat them as a starting point rather than a verdict.
| Foot length (mm) | US Women's | US Men's | Unisex label | UK | EU |
|---|---|---|---|---|---|
| 222–226 | 6 | 4.5 | 4.5 | 4 | 37 |
| 227–231 | 6.5 | 5 | 5 | 4.5 | 37.5 |
| 232–236 | 7 | 5.5 | 5.5 | 5 | 38 |
| 237–241 | 7.5 | 6 | 6 | 5.5 | 38.5 |
| 242–246 | 8 | 6.5 | 6.5 | 6 | 39.5 |
| 247–251 | 8.5 | 7 | 7 | 6.5 | 40 |
| 252–256 | 9 | 7.5 | 7.5 | 7 | 40.5 |
| 257–261 | 9.5 | 8 | 8 | 7.5 | 41 |
| 262–266 | 10 | 8.5 | 8.5 | 8 | 42 |
| 267–271 | 10.5 | 9 | 9 | 8.5 | 42.5 |
| 272–276 | 11 | 9.5 | 9.5 | 9 | 43 |
| 277–281 | 11.5 | 10 | 10 | 9.5 | 44 |
Two rules of thumb fall out of this chart and are worth memorizing: UK = US women's − 2, and UK = US men's − 0.5. One half-size step is about 4–5 mm of length, which is why a "close enough" guess between two rows is a 5 mm error — small on paper, blister-sized in practice.
If your measurement sits at the very top of a row and your foot is also wide, size up rather than sideways. Our guide to wide-foot shoes that don't look orthopedic covers which shapes absorb extra width without adding length.
What do you do when a style is only sold in women's sizing?
Convert your men's or unisex size upward by 1.5 and then check the width, because the length will fit but the last may not. A US men's 8 becomes a US women's 9.5 — but that women's 9.5 is cut roughly a half-width narrower than the men's shoe you're used to, so a standard men's D foot should look for the widest available option or a style with adjustable volume.
This is the single most common sizing trap in fashion e-commerce right now, and it runs in both directions: a women's-only heel with no men's equivalent, or a unisex sneaker that stops at men's 4.5 and leaves smaller feet with nothing. Statista's data shows online channels took roughly a quarter of US footwear sales in 2024, which means most of these decisions now get made without a try-on.
Here's how the main categories compare when you're converting across the gap:
| Category | Usually labeled in | Conversion rule | Typical US price range | Forgiveness if you're between sizes |
|---|---|---|---|---|
| Women's heels & slingbacks | US women's only | Men's + 1.5 → women's | $60–$180 | High — slingback straps adjust; ankle straps stop heel slip |
| Women's flats & loafers | US women's, sometimes EU | EU ≈ women's + 31 | $50–$150 | Medium — removable insole buys about a half size |
| Unisex sneakers | US men's | Women's − 1.5 | $70–$200 | High — laces control volume across the instep |
| Men's leather loafers & dress shoes | US men's + UK | UK = men's − 0.5 | $90–$250 | Low — structured lasts barely stretch; go by mm |
| Boots | US women's or men's, plus EU | As above, then size for socks | $90–$300 | Medium — zip or adjustable shaft helps the calf, not the toe |
In practice, laced and strapped styles convert most safely. The Calvaro Woven Leather Loafers have enough give in the woven upper to absorb a half-size difference, while the structured last on the Beaumont Croc-Embossed Loafers rewards getting the millimeters right the first time. Browse the full women's footwear and men's footwear ranges side by side and compare the mm figure, not the label.
What should you do if your left and right feet are different sizes?
Buy for the larger foot, then adjust the smaller side with an insole or tongue pad — never split the difference. Mild asymmetry is normal; a gap of a half size (about 4–5 mm) or more is common enough that most people who measure both feet properly find one.
The reason this matters more than it sounds: a long-cited American Orthopaedic Foot & Ankle Society survey from 1993 found that 88% of women were wearing shoes narrower or shorter than their own feet, and asymmetry is a big part of why — people size to the foot that feels fine and quietly compress the other one for years.
- Half a size or less: Buy the larger size. Add a thin 2–3 mm insole on the smaller side.
- A full size: Buy the larger size, use a full-length cushioned insole plus a heel grip on the smaller foot to stop slippage.
- More than a full size: Prioritize styles with real adjustment — laces, buckles, ankle straps or elastic gussets — over slip-ons.
- Both feet, all cases: Try shoes on at the end of the day, in the sock thickness you'll actually wear.
Adjustable styles do the heavy lifting here. The ankle strap on the Aveline Slingback Heels locks the heel in place on the smaller foot, and the lace closure on the Amber Grove Olive Shoes lets you tune each side independently. If asymmetry has pushed you toward sizing up across the board, our guide to fixing itchy sweaters is a companion read on the same principle: fix the fit problem at the source instead of tolerating it.
Frequently Asked Questions
Is a women's 9 the same as a men's 7.5?
Yes, in length — both correspond to roughly 252–256 mm of foot. The men's version will be cut wider through the forefoot and heel, so the same number in millimeters can still feel like a different shoe.
Are unisex shoe sizes men's or women's?
Unisex shoes are labeled in US men's sizes almost universally. If a listing says "unisex 8," that's a men's 8, which equals a US women's 9.5 — subtract 1.5 from your women's size to order.
How do I convert my foot length in mm to a US shoe size?
Each half size equals about 4–5 mm. A 250 mm foot is a US women's 8.5 or a US men's 7; use the conversion table above and round up if you fall between two rows.
Should I size up or down when converting between women's and men's?
Convert exactly using the 1.5-size rule first, then adjust for width rather than length. If a converted shoe feels tight across the ball of the foot, look for a wide option — going up a half size adds length you don't need and causes heel slip.
Do EU shoe sizes run smaller than US sizes?
EU sizing isn't smaller so much as less standardized — the same EU 39 can vary by nearly a full size between Italian, Spanish and Portuguese makers. Always cross-check the brand's own millimeter chart before ordering an EU-labeled shoe.
Why do my feet measure different sizes?
Slight asymmetry between the left and right foot is normal and typically ranges from 2 to 8 mm. Buy for the larger foot and pad the smaller one — that's the standard fitting-room approach and it works at home too.
Ready to put your millimeters to work? Explore new arrivals, browse accessories to finish the look, and shop the full footwear edit at oscarblackwood.com — measure once, order confidently.