This takes two minutes and it is the only measurement that works across every brand. You need a sheet of paper, a pen, and a ruler or tape measure.

1. Measure late in the day

   Feet swell over the course of a day and during exercise. An evening measurement reflects how the shoe will actually feel on a run or a ride.

2. Wear your usual socks

   Stand on the paper in the socks you'll wear with these shoes. Thick hiking socks can change the answer by half a size.

3. Trace standing up

   Put your weight on the foot — it lengthens under load. Hold the pen upright and trace the outline.

4. Measure heel to longest toe

   Not always the big toe. Measure in centimetres. Do both feet and use the larger number — almost everyone has one foot bigger than the other.

Sizes are calculated from each brand's own published size chart. Where a brand publishes a Japanese/CM size designation rather than a true foot-length measurement, we apply the 0.5 cm relationship that Salomon publishes between the two. See how this works.

The good news: across the running brands we carry, US sizing is broadly consistent. The differences that actually matter are width and volume, not length — which is why the width section below is worth more of your attention than the conversion table.

If a shoe feels tight across the ball of your foot but your toes have room at the end, you don't need a longer shoe — you need a wider one. Going up half a size to fix a width problem gives you a shoe that slides at the heel and bruises your toenails on descents.

Brooks, New Balance, ASICS and HOKA all use the same letter system, which makes it easy once you know it:

Note the overlap: a women's D is a wide, but a men's D is a standard. Same letter, different meaning depending on which side of the range you're shopping.

• Widest selection

  Brooks and New Balance carry the full four-width range on the most models. If you've struggled to find a shoe that fits across the forefoot, start here.

• Wide as a separate model

  Salomon and Specialized don't use width letters — the wide version is its own product (Speedcross 6 Wide, S-Works Torch Wide). Specialized's wide has a base plate 4 mm wider than standard.

• Volume, not footprint

  HOKA notes that most of the extra room in its wide sizes comes from the upper, which relieves pressure over the top of the foot rather than widening the sole. Worth knowing if you expected a visibly wider shoe.

• Shimano's wide ladder

  Shimano offers three levels: half a size up for a slightly wide foot, the DYNALAST Wide last (about 9–10 mm more circumference at the ball) for a genuinely wide foot, and the Volume Tour last for maximum volume.

The closest size on each brand's own published chart to the measured foot length. Where a brand's range stops, the cell is blank. Giro and DMT aren't shown — Giro publishes no foot-length column, and DMT uses a separate chart for every model.

• Five Ten follows adidas

  Five Ten is an adidas brand and uses the adidas size ladder exactly — identical US, UK and heel-to-toe measurements. If you know your adidas size, that's your Five Ten size. Note the EU numbers come in thirds (42 ⅔, 43 ⅓), so a Five Ten EU 42 ⅔ is a US 9 while a Shimano EU 42 is a US 8.5. adidas states: True to size. We recommend ordering your usual size.

• DMT charts are per model

  DMT publishes a different chart for each shoe, and they differ by up to a full US size — a KR4 EU 41 and an SH10 EU 41 are not the same shoe internally. Always read the chart on the specific product page. DMT does publish a width in cm per size, which is unusually useful if you have a wide foot.

• Sidi has two lasts

  Sidi's newer Millennium Fit is slightly wider and fits a foot about 0.5 cm longer at the same EU number than the classic Regular Fit. A 26.0 cm foot is an EU 42 in Regular but an EU 41.5 in Millennium. Also unusual: a Sidi half size adds upper volume, not sole length — a 44 and a 44.5 share the same sole.

• Giro sizes by EU only

  Giro publishes no foot-length column, so we can't convert it reliably here — use the EU number and Giro's own chart. Giro's wide is designated HV (high volume) in the model name. Giro's women's models use a slightly narrower last than the unisex line.

• Scott runs slim

  Scott labels the Road RC a racing fit with smaller volume and a slim fit, and offers no wide version — instead the shoe ships with high, medium and low volume insoles. If you're between brands and have a wide foot, Scott is the one to try on first.

• The one rule everyone agrees on

  No cycling brand publishes a running-to-cycling conversion — the widely repeated size up half a size for bike shoes has no brand backing. What Shimano does say officially: Go with your normal shoe size, as bike shoes run true to size, and always size up if you have to decide between two sizes because your foot can swell throughout the day.

Birkenstock's own conversion is a formula: women's US size + 31 = EU size, and men's US size + 33 = EU size.

Footbed length is not foot length. Birkenstock's own instruction: add 10 mm to your measured foot length to get the footbed length you need, then read the EU size.

Regular or narrow?

Birkenstock makes the cork footbed in two widths, and you identify them by the small footprint icon printed on the footbed itself:

• Regular — outlined footprint

  Equivalent to a US women's C–D or men's D–EE. The hollow, outline icon.

• Narrow — solid footprint

  Equivalent to a US women's A–B or men's B–C. The filled-in icon. Birkenstock notes that our Narrow width fits most women's feet.

Their test: if there's significant room on either side of your foot on the footbed, you're a narrow. In a correct narrow fit you should still have some space along the sides, and your feet shouldn't ride up on the rims. If the straps are still loose at the last hole, go narrow.

Compare your foot width measurement to the width columns in the table above — that's the reliable way to decide before ordering.

Everything below is the brand's own published guidance. Where a brand publishes nothing, we say so rather than repeating internet folklore.

• Brooks

  Brooks recommends ordering Brooks running shoes a half size to one size larger than what you wear in casual or dress shoes.

  Read that carefully — it's relative to casual or dress shoes, not to other running shoes. Against another running brand, Brooks is true to size. Brooks Korea puts it plainly: select your regular size based on the athletic shoes you normally wear.

• HOKA

  Between sizes? For a more secure fit, try the smaller size. For more freedom for your toes, try the size up.

  One model-specific note from HOKA itself: for the women's Clifton 10, Arahi 8 and Challenger 8, HOKA recommends going down half a UK size from your usual HOKA size — those three moved to a redesigned last.

• On

  On publishes no brand-wide fit statement. Its US retail partners describe the Cloudmonster 3, Cloudsurfer 2, Cloudrunner 3 and Cloudboom Strike as true to size, with a note that the Cloudmonster 3 can run a touch long compared to other On models — worth trying both if you're between sizes.

• Salomon

  If you fall between two sizes, choose the bigger size as your feet will swell during your hike, with a target of about a 1 cm gap between your toes and the end of your shoe.

  Salomon has a reputation for running small and narrow, but Salomon itself publishes no such statement — the size-up advice above is what the brand actually says.

• ASICS

  ASICS recommends a running shoe around a half size larger than the shoe size you usually get, with about a thumb's width between your longest toe and the front of the shoe.

• New Balance

  Choose the larger size if your feet are between sizes. You can adjust for a better fit with socks, insoles and lacing patterns. No model-specific guidance is published.

• Altra

  Altra shoes run true to size in general, but the sizing can vary across different models. Altra notes the Escalante runs slightly narrow, while Torin and Lone Peak fit true. Coming from casual sneakers rather than running shoes, consider half a size to a full size up.

• Specialized

  Specialized shoes fit true to size, but every foot is different. The Wide versions use a base plate 4 mm wider than standard, in the same EU numbering — you don't change size number to go wide.

• Shimano

  Go with your normal shoe size, as bike shoes run true to size. Shimano describes cycling shoes as designed to fit very close to the foot, almost like a second sock — snugger than you'd accept in a running shoe, and that's correct.

• Sidi

  Measure the length of the foot in cm, from the heel to the big toe. If the foot length falls between two sizes, we recommend choosing the larger one. Sidi's wide models are badged Mega; on models updated to Millennium Fit, the extra volume is built in and Mega is no longer offered.

• fizik

  fizik declines to give a conversion rule: the choice of the shoe size is very personal, so it is difficult to give you an advice behind a screen. They publish a printable sizing grid instead — print at 100% scale and stand on it barefoot. Their Wide models add a higher-volume ball and broader metatarsal area.

• Birkenstock

  Aim for about ¼ inch of space around the foot, with toes clear of the front edge. Flex the footbed by hand before first wear, keep the straps loose, and build up from an hour or two indoors as the cork moulds to your foot.

Every number on this page comes from the brand's own published size chart. That sounds obvious, but it's the reason this guide disagrees with some others you'll find.

The catch is that brands publish two different measurements under similar-looking headings. Some — HOKA, Salomon, fizik, Sidi — publish true foot length, the number you get from tracing your foot. Others publish the Japanese size designation, which is a size label that already includes the toe allowance built into the shoe. Salomon happens to publish both side by side, and the gap between them is a consistent 0.5 cm: their JP 25 shoe is built for a 24.5 cm foot.

So where a brand gives us a Japanese/CM designation rather than a foot measurement, the size finder above applies that same 0.5 cm relationship, which puts every brand on a like-for-like footing. Charts that skip this step are the reason a customer can be told they're a 9 in one brand and a 10 in another when in reality both shoes fit the same foot.

Where a brand publishes nothing usable — Giro's foot length, Merrell's, DMT's single universal chart — we've left it out and said so rather than filling the gap with an estimate.