Running Shoe Size Guide: Should You Size Up?

Most runners are wearing the wrong size shoe. Not a little wrong — meaningfully wrong. A study by the College of Podiatry found that nearly two-thirds of runners wear shoes that are too short or too narrow. The consequences show up in training logs and medical waiting rooms: black toenails, blisters under the ball of the foot, plantar fasciitis flare-ups, and bunions that weren't there a year ago.

The problem isn't that runners don't care about fit — it's that shoe sizing is genuinely complicated. Your street shoe size is not your running shoe size. Hoka sizing is different from Nike sizing. The Hoka Clifton fits differently from the Hoka Bondi. There's no single answer, and most resources give you either vague generalities or marketing copy.

This guide covers the fundamentals of running shoe sizing: why running shoes fit differently, how to measure your feet properly, whether to size up (and by how much), and what width options actually mean. We've also pulled in real fit data from the RunSized community so you can see how specific brands and models behave in practice.

Why Running Shoes Are Different From Regular Shoes

Your feet are not static objects. During a run, they swell — sometimes by as much as half a shoe size or more. This happens because repeated impact drives fluid into the tissues of the foot, and because the sustained cardiovascular effort increases blood volume in your extremities. The longer and hotter the run, the more your feet expand. A shoe that felt perfect in the store at 10am on a cool morning can feel like a vice grip at kilometre 25 on a summer afternoon.

Running also demands active toe movement in a way walking doesn't. Your toes splay outward on each foot strike to help with balance and propulsion. A toebox that doesn't allow this doesn't just cause blisters — it can alter your gait and load your plantar fascia unevenly. Enough runners have learned this the hard way that “foot-shaped toebox” is now a genuine selling point for brands like Altra and Topo Athletic.

Two more variables that don't apply to dress shoes: lacing and sock thickness. Different lacing patterns can dramatically alter how a shoe wraps the midfoot. And running socks range from paper-thin race-day socks to thick winter merino — that difference can eat up a half size of fit latitude.

The rule of thumb that's stood the test of time: you should have approximately one thumb's width of space between your longest toe (which isn't always your big toe) and the end of the shoe. Not a pinky-finger width. Not two fingers. One thumb. That's your starting point.

How to Measure Your Foot for Running Shoes

The Brannock device — that metal foot-measuring thing you see in shoe stores — is still the gold standard. It measures length and width simultaneously and accounts for arch length (where your arch meets your ball), which is often more relevant than overall foot length. If you haven't been measured with one since you were a teenager, go find one. Most running specialty stores have them and will happily measure you.

No running store nearby? The tracing method works reasonably well. Stand on a piece of paper (weight-bearing matters — your foot is longer when you're standing), trace around your foot with a pencil held vertically, then measure the longest and widest points. Compare against your target brand's size chart.

Two non-negotiable rules for measuring:

• Measure at the end of the day. Feet swell throughout the day from standing and walking. A measurement taken first thing in the morning can be half a size shorter than your end-of-day foot.
• Measure both feet and fit the larger one. It's extremely common to have feet that differ by a quarter to half a size. If you fit the smaller foot, the larger one will suffer.

Width is the other dimension runners overlook. Standard men's width is D (also called medium). Standard women's width is B. If your foot is wider than average, 2E (wide men's) or D (wide women's) may be what you need — and many brands now offer these options across their core models. Going up a size to accommodate width is a common workaround, but it's not ideal — you end up with a shoe that's too long in the heel, which creates its own problems.

Do Running Shoes Run True to Size?

The honest answer: it depends on the brand, the model, and sometimes the year (brands occasionally change lasts between versions). Here's a rough guide based on what RunSized community members report, supplemented by widely-reported consensus across running forums:

RunSized tracks fit reports from real runners — not marketing copy. When someone submits “I wear New Balance 1080 in US 10D and I bought the Hoka Clifton in 10.5, which fit true to size,” that data point joins thousands of others to give you a statistically grounded answer rather than a guess.

Should You Size Up in Running Shoes?

The general rule: yes, by about half a size compared to your street shoe size. This accounts for foot swelling during the run and gives your toes room to move. It's not a guarantee — some brands run long already and don't need it — but it's the right starting point for most runners in most shoes.

When to size up more (a full size or even 1.5):

• Long distances. Half marathon and beyond, your feet swell more. Many ultramarathon runners go up a full size and sometimes carry a second pair of shoes a size larger for the back half of a race.
• Hot weather running. Heat accelerates fluid retention in the feet. If you're training through Australian summer, factor this in.
• Wide feet in a narrow last. Sometimes sizing up is the only way to get enough toebox width when your target shoe doesn't come in wide options.

When not to size up:

• Racing shoes. Carbon-plated race shoes (Vaporfly, Metaspeed, Endorphin Pro) are designed for a snug fit to maximise energy return. Many runners actually wear their race shoe true to size or even half a size down from their training shoe.
• Minimalist and zero-drop shoes. Brands like Altra design with a foot-shaped toebox that already gives ample room. Sizing up can result in heel slippage that creates its own problems.

Running Shoe Width Guide

Width is the most underrated dimension in running shoe fit. Many runners size up in length to compensate for width issues — which is the wrong solution. Here's what the standard width codes actually mean:

Brands that tend to run narrow: Nike (especially race shoes), Asics (standard width), Saucony Kinvara. If you have a wide forefoot, approach these with caution or seek out their wide variants.

Brands that tend to run wide or have best-in-class width options: New Balance (most models offered from B through 4E), Brooks (Ghost, Glycerin, Adrenaline all come in wide), and Altra (foot-shaped toebox on all models). Toebox shape matters independently of width code — a shoe listed as standard D width can still have a tapered toebox that squeezes toes.

How RunSized Can Help

General sizing rules only get you so far. The real question isn't “should I size up in running shoes” — it's “what size should I order in the specific shoe I'm about to buy, given the shoe I know fits me?”

That's what RunSized answers. Our database is built from community fit reports: runners who own a shoe they know fits, bought a new shoe, and reported back with the size they ordered and how it fit — too long, true to size, too short, narrow toebox, wide enough for bunions, whatever. Those reports aggregate into model-level fit profiles you can actually trust.

The more runners contribute, the better the data gets. If you've recently bought a running shoe, a two-minute fit report makes the tool more useful for the next person facing the same decision.

Frequently Asked Questions