Choosing running socks by foot length, not shoe size

Most sock labels give a range of shoe sizes. That seems simple until you notice that your running shoes, cycling shoes and everyday shoes are not all the same size, and that a UK size from one brand is not always the same foot as an EU size from another. Foot length in centimetres is a better starting point, because it does not change with the shoe.

Why shoe sizes are a poor guide

A shoe size describes a shoe, not a foot. Each shoe maker builds on its own lasts (the foot shapes that shoes are made round), adds its own allowance for room at the toes, and converts between UK, EU and US sizes in its own way. Running shoes are often bought a little longer than everyday shoes, and cycling shoes have their own sizing again. So the same foot can wear several different numbers.

Sock makers then group shoe sizes into bands, such as S, M and L, and the bands differ from maker to maker. If you only know your shoe size, you are converting twice. If you know your foot length, you can read the sock maker's table directly.

How to measure your foot

You need a sheet of paper, a pen, a ruler or tape and a wall.

1. Put the paper on a hard floor, with one short edge against the wall.
2. Stand on it barefoot, with your heel against the wall and your weight even on both feet.
3. Mark the tip of your longest toe. For many people that is the big toe; for some it is the second toe.
4. Step off and measure from the edge of the paper, where your heel was, to the mark, in centimetres.

Stand while you measure. A foot spreads and lengthens a little under your weight, and that is the foot your socks have to fit. If you can, ask someone else to make the mark, because leaning down to do it shifts your weight.

Both feet, in the evening

Measure both feet. Many people have one foot slightly longer than the other, and you should size to the longer one.

Measure later in the day if you can. Feet tend to be a little larger in the evening than first thing in the morning, after a day of walking and standing, and an evening measurement is closer to your feet on the move.

Sock size bands

Sock sizes are bands, not single sizes. Each band covers a range of foot lengths, or a range of shoe sizes the maker has matched to foot lengths. Knitted socks stretch, so a sock fits across its band, but the ends of a band still matter.

• Near the bottom of a band, the sock is long for you. The heel pocket can sit behind your heel rather than under it, and spare fabric can wrinkle inside the shoe.
• Near the top of a band, the sock is short for you. It can pull tight across the toes, and the heel can creep down under your foot as you run.

Running socks with a shaped left and right foot, or an elastic band round the arch, are less forgiving than a plain sock, so getting the band right matters more.

Enter your foot length in the fit finder and every pair of socks shows its size from the maker's own table. When you are within half a centimetre of the line between two bands, you see both: the larger as room to layer, the smaller as close fit. A thin running sock usually feels best without spare fabric, while a thick winter sock may suit the larger band. It is your choice; the maker's table only tells you where your foot sits.

Compression socks and calf sleeves

Compression socks and calf sleeves are sized differently. The pressure they give depends on how far they stretch round your leg, so makers size them by calf circumference, sometimes together with foot length or ankle circumference.

To measure your calf:

1. Stand with your weight on both feet, or sit with your foot flat on the floor if the maker asks for that.
2. Wrap the tape round the widest part of your calf.
3. Keep it level and snug, without squeezing.

Some makers ask you to measure in the morning, before your legs have had a day on them. Follow the instructions that come with the size table.

Add your calf measurement to the fit finder, and compression socks and calf sleeves in sleeves and warmers show their size from the maker's table. On a compression product, a larger size usually feels looser and a smaller one firmer. If you are between sizes and the maker gives advice for that case, follow it.

Cycling overshoes

Overshoes go over your cycling shoes, not your bare feet, so they are made to fit round a shoe. Makers usually size them by shoe size, and some by foot length. Where a maker's table uses foot length, the fit finder reads it like any other table. Where it uses shoe size, go by your cycling shoes rather than your running shoes, and read the maker's notes on cleats and fastenings. A shoe with a buckle or a dial takes up more room than a smooth one.

Socks and shoes together

When you buy new running or cycling shoes, try them on with the socks you plan to wear. A thick winter sock takes up noticeably more room than a thin summer one, and a shoe that is just right with one can be tight with the other.

Keep your numbers in one place

Your foot and calf measurements stay in the fit finder alongside your hand and head, so you only measure once. As a guest they are kept in a cookie on this browser; signed in, they are kept in your account and follow you to other devices. "Forget my measurements" clears them whenever you like.

To browse everything that has your size, open the shop and turn on the Fits me filter. For gloves, our guide on measuring your hand works the same way, and Shipping and returns explains what to do if a size is not right.