How Should Running Shoes Fit? Choosing the Right Size

10 min read

When sizing running shoes, you want a thumbnail’s space between your longest toe and the front of the shoe. The shoe itself should fit tight around the big toe, but light around the pinky toe.

The heel of the shoe should feel stable and firm on your foot. The mid-shoe area should be a little tight, but come off with little effort when you’re unlaced.

Hi, I’m Karim Maghraby. I’m a physician scientist (M.D., M.Sc.) and an avid runner.

Today, I’m teaming up with running coach Sergey Schepin answer “how should running shoes fit?”

We’ll cover:

  • Toe fit
  • Mid-Shoe Fit
  • Heel fit
  • Shoe length and shape

Let’s start!

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Disclaimer: This guide was created for educational purposes. It neither offers nor replaces medical advice. Learn more here.

Table of Contents

1

Toe Fit

You should have a thumbnail’s space in front of the longest toe. This extra space is necessary for two reasons.

First, our feet are bigger than usual when we’re running. Exercise makes blood rush to them; the force of impact spreads them against the ground. This results in a longer, wider foot.

Another reason is that toes flex and curl when you run. Having a longer toe box lets them do this freely. It also lets the shoe flex together with the foot.

This applies to road and trail running shoe models. It applies to most racing models too.

There are three exceptions:

  1. Racer models with stretchy, flexible toe boxes. These use components like carbon fiber plates to give you flex and room without running long.
  2. Fingered, barefoot-style running shoe models. If you’re running in a pair of Vibrams, the shoe will stretch in the mid-section rather than in front.
  3. Cross training shoes. If you’re not going to do much running in these, 1/2-2/3 of a thumbnail’s width is okay.

Toe Fit Test

Stand up in your shoes and use your fingers to feel out the toe box. The big toe area should be snug. There should be about a thumb’s width between the longest toe and the shoe front.

2

Mid-Foot Fit

The midfoot (or instep) is the space from the bottom of your arch to the bony top of your foot.

For a perfect fit in this area, look for a shoe that:

  • Has a firm but comfortable grip and doesn’t restrict blood flow.
  • Fits your natural foot shape and supports your instep.
  • Feels firm but comfortable when laced up.

We’re looking for a snug fit that isn’t too tight. Shoes that are tight in the middle can immobilize and constrict the foot. This can affect your gait and cause foot pain.

Mid-foot Fit Test

Run your finger between your shoelace knot and shoe. You should meet some resistance, but not so much you have to jam your finger in.

3

Heel Fit

The heel keeps the back of your foot in place. It can also stabilize your gait, guiding the foot from heel strike to toe-off.

Look for:

  • A firm fit. You want no heel slippage and no friction around the back of the foot.
  • An appropriate amount of cushioning. This varies by individual, so be mindful of personal preference.
  • A comfortable heel counter.

Not sure what a heel counter is? It’s a rigid construction in the back of a running shoe. It cradles your heel, keeping it stable when you’re running.

The wrong heel counter can dig into your heel, hurting you when you run. You may be able to fix this with a thicker sock, but it’s best to avoid the problem altogether. Look for running shoes that don’t dig into the back of your foot.

Heel Fit Test

Run your finger between your heel and the shoe. You should be able to slide it through with little pressure.

Now stand in the shoe and lift your heel off the ground. The heel should remain firmly on the foot without rubbing it.

4

Shape

If you followed our instructions so far, your shoe is the right length already. But shape is important too.

The shoe should be shaped in a way that doesn’t constrict or squeeze your foot.

Each shoe brand has its own shoe shapes. This is why many runners buy from the same brand repeatedly. Here’s a simple shape test.

Shape Test

  1. Remove the insoles or foam pads in your shoes. 
  2. Place the insoles on the ground and stand on them.

If your feet go way over the edges of the insole or foam pad, the shoe may not be the best shape for you. 

5

Support

Your shoe needs to be a good fit for your arch shape and foot posture.

This is important. Let’s say you have a high arch and your foot rolls outward. If you get a shoe for pronators, they’ll make the foot roll outward even more. This can lead to sprained ankles and other problems.

As a rule:

  • Runners with flat feet are likely to overpronate. They can benefit from a stability shoe that corrects pronation and arch height.
  • Runners with elevated arches are likely to supinate. They can benefit from a stability shoe that corrects supination and arch height.
  • Runners with neutral arches need a neutral shoe. Sometimes, they need light pronation correction.

Here’s a helpful chart to help you remember:

Not sure what your arch is? Just do the wet test. 

  • Get your feet wet using a bath, bucket of water, or sponge.
  • Step on a piece of paper or cardboard for a second or two.
  • Remove your foot from the paper or cardboard.
  • Look at the imprint left and compare it to the images below.

If you can see most of your foot, your arches may be low or flat.

If you can see around half of your foot, your arches are in the normal range.

If you don’t see half or more of your foot, you likely have high arches.

Got high or low arches? Visit a specialized store to check yourself for pronation or supination. If you can’t or won’t do that, look at your shoe soles.

If the outside of your shoe has more wear, you supinate. If the inside of your shoe has more wear, you pronate.

Our editor is a supinator with high arches, so his soles look like this:

General Tips

  1. Be mindful of the time of day. Our feet swell up by the end of the day, changing our shoe size. For a perfect fit, try shoes on later in the day or around your usual running time.
  2. Running makes our feet swell, tighten, and warm up (2). This changes the way our shoes fit. For an optimal fit, try new shoes on after exercising.
  3. Our feet are rarely symmetrical. As a result, your left and right shoe may have different fits. When in doubt, buy pairs of shoes that fit your larger foot.
  4. Wear your regular running socks when fitting new shoes.
  5. Don’t underestimate the importance of shoe sizing. A poor-fitting shoe can cause foot problems like (3):
    • Black toes
    • Bunions
    • Pain and fatigue
    • Blistering
    • Chafing

Why Don't My Shoes Fit Properly?

One reason your shoes may not fit is size variance. A Size 9 in Adidas Superstars is not going to fit exactly like a Nike React Size 9. Moreover, two different Adidas shoes may differ in length, shape, width, etc.

This makes it hard to figure out your exact size and, in turn, find shoes that fit properly.

To complicate matters further, our own feet change with time. For instance, they tend to become narrower and either shorter or longer as we age. Their shape may also change with time, especially if you have blisters, flat feet, bunions, etc.

The best solution is to size new shoes before buying them. This way, you know for sure whether it’s the right size for you.

Another alternative is to buy shoes from one brand or one model family. Unfortunately, this method isn’t very reliable.

Different model versions can have different toe boxes, heel counters, or mid-shoe materials. Ditto for different-gender shoes made by the same brand. The only way to know a shoe’s fit is to try it on, even with brands you’re familiar with.

Should I Go for a Fitting or Measure My Own Feet?

If you’ve never been fit for running shoes before, consider getting one now. A proper fitting will give you a baseline idea of your foot’s ‘perfect fit’. This will make it easier to buy shoes that fit well, even if your foot changes over time.

A running shoe store will usually measure your feet with a Brannock device (4). A doctor is likely to use a specialized foot scanner that tracks foot length, shape, arch, width, etc. Either way, what matters is that you get detailed, accurate measurements.

You can show these measurements to a shoe store employee and ask them for matching models. You can also use it to shop online and compare your foot dimensions to shoe dimensions. Either way, you’re going to get a better fit.

This is especially true if you can find a knowledgeable shopping assistant. Your measurements will make it easy for them to find a shoe that matches your foot type, length, and shape.

I recommend you remeasure your feet every 12 months. Foot size and shape changes with age. Regular resizings will help make sure you’re always wearing the right footwear.

3 Ways to Make Sure Your Shoes Fit Right

1 – Once you’ve chosen a pair of shoes and tried it on, stand up and see how you feel. Your toes should have some space to move around (about a finger’s width). The shoe should exert no pressure on the pinky toe while giving the big toe a firm grip.

2 – Try walking, jumping, or running in your new shoes. Make sure the heel counter has a firm hold on your ankle and doesn’t slip. Make sure it doesn’t dig nor rub into the back of your foot.

3 – Check your mid-shoe area. Can you run your thumb between the shoelace knot and the shoe tongue? You should feel some resistance, but not too much. If this area is too tight or too loose, consider trying a different size.

Don’t rush here. Take your time and make sure your shoe fits you well.

Don’t count on your shoe shrinking, stretching, or ‘breaking in’. It may soften in some areas, but its size and shape won’t change. Keep experimenting until you find a pair that’s just right.

Sizing Online Shoes Before Online Purchases

Start by measuring foot size with our printable Brannock device.

The instructions are:

  • Open the .pdf file and print it on a sheet of A4 paper.
  • Put on a pair of socks similar to the one you run in.
  • Place a ruler (or any straight edge, like a clipboard) on the red line where the right/left heel is marked. Make sure you’re using the correct side for each foot.
  • Stand up and place your heel against the straight edge with your foot flat on the floor. You may want to place the printout, and your foot, next to a wall to make this easier.
  • Using your longest toe, record your foot length. If your feet aren’t the same size – most people’s aren’t – use the longer foot’s measurement.

Once you know your foot size, convert it into the shoe size of whichever brand you’re shopping for. Then buy the shoe. 

In Summary

Now you know exactly how running shoes should fit.

Make sure:

  • Your toes have a thumbnail’s space in front of them.
  • The toe box has a light grip on your pinky toe and a firm one on the big toe.
  • Your shoes are tight around the middle when laced up but easy to remove when unlaced.
  • Your heels feel stable, with no friction or slippage.

References

  1. Janisse, D. J. The Art and Science of Fitting Shoes. Foot Ankle 13, 257-262 (1992).
  2. McWhorter, J. W. et al. The effects of walking, running, and shoe size on foot volumetrics. Phys. Ther. Sport 4, 87-92 (2003).
  3. GOONETILLEKE, R. S. Designing footwear: back to basics in an effort to design for people. Proc. SEAMEC 7 (2003).
  4. Brannock, C. F. Foot measuring device. (1960).

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Writer:

Dr. Karim Maghraby

Last Updated:

April 30, 2022

DR. KARIM MAGHRABY

Dr. Maghraby is a medical doctor and published physician scientist. He’s an avid runner and a user of sports compression gear.