How to Measure Foot Size at Home, and Why Both Feet
Shoe sizing has a real ruler behind it, and one rule most people skip. Here is how to measure at home, which foot to fit, and what the numbers convert to.
Shoe sizing is in better shape than clothing sizing, because there is an actual unit underneath it. It is just a strange one: the barleycorn, “an old English unit that equates to 1⁄3 inch (8.5 mm). This is the basis for current UK and North American shoe sizes.”
One barleycorn is one shoe size. That is why sizes step by a third of an inch, and it is why the whole system can be written as arithmetic — which we will get to. First, the measurement, because everything else is downstream of it.
Measure both feet. Fit the larger one.
This is the single rule that changes outcomes, and it comes straight from Brannock, who make the foot-measuring device you stand on in shoe shops. Their own fitting instructions say: “Be sure to measure both feet, then fit the larger foot. It is common to have feet of different sizes.”
Note the wording: common, which is Brannock’s, not ours. That is enough to make measuring one foot a coin toss you have no reason to take — and no amount of breaking in fixes a shoe bought to the smaller foot.
Two more instructions from the same source, both easy to get wrong at home:
- Stand with your weight even on both feet. Brannock’s wording is that you should “stand with equal weight on both feet to ensure that the foot being measured has elongated and spread to its maximum size.” Measuring seated gives you a shorter, narrower foot than the one that will be in the shoe.
- Measure at the right time of day. “Have footwear fitted at a similar time as when you will be wearing the footwear. For daily footwear go when you’ve been on your feet all day your feet have expanded.” For everyday shoes, measure in the evening.
The home method
You need a sheet of paper bigger than your foot, a wall, a pencil and a ruler.
- Put the paper flat against a wall, on a hard floor. Carpet compresses and adds length.
- Stand on it with your heel against the wall, wearing the socks you would wear with the shoes. Weight even on both feet.
- Mark the longest toe — not automatically the big toe. Brannock’s instruction for reading length is to “look straight down over the longest toe (not necessarily the first toe)” — their parenthesis, and the reason to check rather than assume.
- Mark the widest points on each side of the ball of the foot, at the same time.
- Step off and measure. Heel to toe mark for length; across for width. Record in both inches and centimetres.
- Repeat for the other foot on a fresh sheet, and keep the larger set of numbers.
Have someone else mark if you can. Leaning down to draw around your own foot shifts your weight and pulls the reading short.
Turning length into a size
Your foot length is not your shoe size, and the gap is not an error. Shoes are built over a last, “the foot-shaped template over which the shoe is manufactured,” and a last runs longer than the foot it is for — typically “1⁄2 to 2⁄3 in or 1+1⁄2 to 2 barleycorns.” That extra room is deliberate, and the conversions already account for it.
The approximate formulas, from foot length:
| System | Formula |
|---|---|
| UK (adult) | size ≈ 3 × foot length (in) − 23 |
| US women’s | size ≈ 3 × foot length (in) − 21 |
| US men’s | size ≈ 3 × foot length (in) − 22 |
| EU (Paris points) | size ≈ (3⁄2 × foot length (cm)) + 2 |
A 10-inch foot comes out at a UK 7, a US women’s 9, and — at 25.4 cm — an EU 40.
Two things fall out of those formulas. US women’s sizes run two numbers above UK sizes, because the constants differ by two. And US men’s run one above UK: the same shoe “would be marked 13 in the US and 12 in the UK.”
Why conversion charts contradict each other
Because the offsets are not actually fixed. The one-size men’s difference is the nominal standard, but “most US manufacturers are using offsets greater than that standard; some offset by 1⁄2 barleycorn, others by 1 barleycorn.”
Wikipedia’s shoe size article puts the consequence bluntly: “Conversion tables available on the Web often contain obvious errors, not taking into account different zero points or wiggle room.” Including, to be fair, the risk in the table above — which is why it is labelled approximate and why the brand’s own chart wins.
Width is the measurement nobody takes
Length gets all the attention, and width is where most of the discomfort actually lives. The Brannock Device reads it directly: “Slide the width bar firmly to the edge of the foot. Locate the shoe size … on the movable width bar and view the width measurement indicated.”
Note what that instruction implies — width is read against the length. A given width in inches is a different letter at a different size, because a wide foot means wide for that length. This is why “I need a wide” is not portable between sizes, and why a width letter without a size attached means very little.
There is a third measurement the device takes that almost no home method captures: arch length, the heel-to-ball distance, taken by fitting a pointer to “the ball joint of the foot.” A shoe flexes at its own ball point, and if your foot’s ball sits behind or ahead of the shoe’s, the shoe fights you at every step even when the length is right. If a pair measures correct and still feels wrong across the front, that mismatch is the usual suspect, and it is worth getting measured properly in a shop.
Related reading
Foot length is the fourth of the four numbers worth keeping on your phone. The other three, and why brand charts disagree at all, are in our clothing size chart women guide. The clothing side of UK-versus-US labelling — which runs on a completely different offset from shoes — is in uk size 6 to us, and the other garment measurement worth taking properly is how to measure inseam women. The rest are in size guides.
Sources
- Brannock Device instructions and fitting tips — measuring both feet and fitting the larger, equal weight, time of day, reading the longest toe, arch length and width, all quoted verbatim
- Shoe size — Wikipedia — the barleycorn, the UK/US/EU formulas, the last and its extra length, the US/UK offsets, and the warning about online conversion tables
Frequently asked questions
Should I measure one foot or both?
Both, and then fit the larger one. The Brannock Device's own instructions say to measure both feet and fit the larger foot, because it is common to have feet of different sizes. Measuring only one foot is an easy way to end up with a pair that fits on one side and not the other.
Does it matter what time of day I measure?
Yes. Brannock's fitting guidance is to have footwear fitted at a similar time to when you will wear it, and notes that feet expand after you have been on them all day. An evening measurement is the safer one for everyday shoes.
Why is my measured length not my shoe size?
Because shoes are built over a last, a foot-shaped template that runs about half to two-thirds of an inch longer than the foot itself. The size conversions build that extra length in, which is why you convert rather than read your foot length off a ruler as a size.
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