Running Shoe Size: How to Find Yours (Even Online)

To find your running shoe size, especially when buying online, do not rely on the number you wear in everyday shoes. Measure the length of your foot in centimetres, look that length up in the size chart of the brand you want to buy, and check that the shoe leaves about 1 cm, roughly a thumb's width, in front of your longest toe. Those three steps prevent most sizing mistakes.

This guide covers sizing only. If you have not yet decided what kind of shoe you need (road or trail, cushioning, drop), start with how to choose running shoes.

Why your everyday shoe size does not work

There are three reasons the usual number fails for running shoes:

• Brands size differently. A UK 8 or EU 42 is not the same length in every brand, and sometimes not even between two models of the same brand.
• Your foot needs room when you run. With impact and warmth the foot swells slightly and slides forward a little with each stride, especially downhill.
• Many people already wear the wrong size. In a review of 18 studies, Buldt and Menz (2018) found that between 63 % and 72 % of participants wore shoes that did not match the length or width of their feet. The studies covered very different groups, so this is not a figure about runners specifically, but it shows that "my usual size" is a weak starting point.

Step 1: measure your feet in centimetres

You need a sheet of paper, a pencil, a ruler and a wall.

1. Measure in the afternoon or after walking for a while. The American Academy of Orthopaedic Surgeons (AAOS) recommends trying on athletic shoes at the end of the day or after a workout, because feet are slightly larger then.
2. Put on the socks you will run in.
3. Place the paper on the floor against the wall and stand on it with your heel touching the wall and your weight evenly spread.
4. Mark the tip of your longest toe. That is not always the big toe; for many people it is the second toe.
5. Measure in a straight line from the edge of the paper (the wall) to the mark.
6. Repeat with the other foot. A small difference between the two is normal.

Write down both numbers and use the larger one. That is your reference for every size chart.

If you like, also measure the width at the widest part of your forefoot. Not every brand lists widths, but the number helps when you compare standard and wide versions.

Step 2: understand what each sizing system measures

Brand charts mix several systems. You do not need to memorise them, but knowing what each one measures explains why conversions between brands never quite line up.

System	Based on	Step between sizes
Centimetres or Mondopoint (sometimes "JP" or "CM")	Foot length; the Mondopoint system is defined in the ISO 9407 standard and expressed in millimetres	Usually 0.5 cm
EU	Paris points: each size is two thirds of a centimetre	About 6.7 mm per size
UK and US	Each full size is one third of an inch	About 8.5 mm per size, 4.2 mm per half size

Two practical consequences:

• The centimetre column is the only one you can compare directly with your foot. The others are labels.
• EU, UK and US sizes advance in different steps, so they never match exactly. Each brand rounds in its own way, which is why the same EU size can be paired with different centimetre values depending on the manufacturer. US sizes also differ between men's and women's shoes.

For the same reason this guide has no general conversion table: it would be right for one brand and wrong for the next. Always use the official chart of the brand you are buying.

Step 3: find your length in the brand's chart

Open the size guide on the manufacturer's website, not a generic one from a retailer, and find the centimetre column. One detail matters here, because brands do not all put the same thing in that column:

• If the column shows foot length (the most common case, sometimes labelled "foot length", "CM" or "JP"), choose the row that matches your measurement or the next one up. The room in front of the toes is already built into the shoe.
• If the column shows the inner length or insole length, add about 1 cm to your measurement and look for that value.

If the chart does not say which it is, look in the notes of the size guide or ask customer service before ordering. It takes two minutes and can save a return.

Worked example

A made-up case: Maya measures her feet in the afternoon and gets 24.3 cm on the left and 24.6 cm on the right. Her reference is 24.6 cm.

• Brand A's chart has a "foot length" column with rows for 24.5 and 25.0 cm. Because 24.6 is above 24.5, she picks the 25.0 cm row and reads off the size that brand gives for it.
• Brand B publishes insole length. Maya adds 1 cm (25.6 cm) and picks the nearest insole row above that.

She will probably end up with different size labels in the two brands, and both can be correct.

Step 4: how much room to leave in front

The classic rule is a thumb's width between your longest toe and the tip of the shoe while standing. The AAOS puts a number on it in its guide to athletic shoes: at least half an inch, about 1.3 cm. In practice most runners end up somewhere between 1 and 1.5 cm. Read that as a rough range, not an exact measurement, because the shape of your toes and of the toe box both play a part.

Too little room shows up as sore or blackened toenails and blisters on the tips of your toes after downhill running. Too much room shows up as a sliding foot, a slipping heel and rubbing.

Step 5: test them at home before you run in them

When the parcel arrives, do this check in the afternoon, in your running socks, on a clean floor, so you can still return the shoes:

• Insole test: take the insole out, stand on it and see how much is left in front of your longest toe. It should be about a thumb's width.
• Length with the shoe on: standing, press down on the toe box with your thumb and find your longest toe.
• Width: your forefoot does not bulge over the sole and there is no pressure on the little toe.
• Heel: when you walk and jog a few steps, the heel does not lift out. A tiny bit of movement is normal.
• Instep: the laces close without pressure points.
• Both feet: always try the full pair, because your feet are not identical.
• Toes: you can wiggle them freely.

If you are between two sizes, remember that a running foot needs more space than a standing one. The larger size is usually the better choice, as long as heel and midfoot are held securely. If the larger one is loose and the smaller one pinches, the problem is the shape of the shoe: try another model or a wide version.

Signs that the size is wrong

What you notice	Possible cause
Sore or black toenails, especially after descents	Shoe too short
Blisters on the tips of the toes	Shoe too short or toe box too narrow
Tingling or numb toes	Shoe too narrow or laces too tight
Heel blisters, heel lifting out	Shoe too long or heel not held
Foot sliding forward downhill	Shoe too long or laces too loose
Rubbing on the little toe	Shoe too narrow for your foot

These clues point in a direction, but they are not a diagnosis. Pain that persists, always appears in the same spot or does not improve with a different shoe is a reason to see a doctor, physiotherapist or podiatrist. The same applies if you have diabetes, circulation problems or a foot deformity: in those cases have the fit of your shoes checked by a professional.

Buying online without surprises

• Read the return policy before you pay: the deadline, the cost and whether shoes tried indoors are accepted.
• Check reviews for sizing comments on the exact model. If many people say it "runs small", take note, but decide from your measurement.
• If you are re-buying a model, check whether the version has changed. The shape can differ from one edition to the next.
• Order two sizes only if returns are free and simple. Then you can compare calmly.
• Keep the box and do not wear them outside until you are sure.

Common sizing mistakes

• Converting sizes between brands by guesswork. Use centimetres.
• Measuring in the morning, sitting down or barefoot.
• Measuring only one foot.
• Choosing a snug size "because they will stretch". Modern running shoes hardly stretch in length.
• Going up a size to gain width. If width is the issue, look for a wide version.
• Assuming your size never changes. Feet can change over the years, with weight changes or after pregnancy. Measure again from time to time.

Summary in five steps

1. Measure both feet in centimetres in the afternoon, standing, in running socks.
2. Use the larger measurement.
3. Find it in the brand's official chart and check whether the chart shows foot length or insole length.
4. Make sure about 1 cm will be free in front of your longest toe.
5. Test the pair at home with the checklist and send it back if it does not fit.

With the size sorted, the next step is using them. If you are just starting out, our guide on how to start running and the run-walk method help you begin without overdoing it, and the beginner 5K training plan takes you to your first race.

Sources

• American Academy of Orthopaedic Surgeons (AAOS), OrthoInfo: Athletic Shoes.
• International Organization for Standardization: ISO 9407:2019, Footwear, Sizing, Mondopoint system of sizing and marking.
• Buldt AK, Menz HB (2018): Incorrectly fitted footwear, foot pain and foot disorders: a systematic search and narrative review of the literature. Journal of Foot and Ankle Research.