Some shoes, even from the same company, may fit differently. Here’s why.

Our gear editors get flooded with running shoe questions. One of the most common: “How does that shoe fit?” That’s because even though you may have worn a size 10 in a certain Nike running style, you may need to choose a 9.5 in a New Balance, a 10.5 in an Asics, or even something entirely different for your next Nike pair.

Finding the right fit for your perfect pair of running shoes includes dealing with sizing discrepancies across brands. Fortunately for runners in the modern age, sizing differences between shoe brands have largely leveled out. But they still exist.

Brands use lasts, a foot-shaped block around which a shoe is constructed, to create shoes and those lasts have a major impact on fit. A last isn’t the only defining factor, though, as the breadth of materials used in the running space can impact the way shoes fit. As brands learn more about fit, each iteration of a popular shoe can have a slight change, too.

The last leads fit: In shoemaking, the last is the three-dimensional model the shoe is “literally built—or lasted—around,” says Simon Bartold, a podiatrist with decades of experience in the footwear industry, including shoe development roles at Asics and Salomon.

To look at it, the last resembles a foot, except that most lasts have a completely flat bottom. “The last and the lasting of the shoe are primarily responsible for fit and comfort, and will determine the volume of the shoe,” Bartold says. “Every shoe company has its own lasts, usually just one for key running models, and they are a closely guarded secret because if you get the last right, the shoe is likely to work.”

This solid mold, which dictates the shape and volume, defines everything from toe shape to heel shape, says Caroline Bell, content specialist and shoe fitter at Fleet Feet.

While the last is the biggest factor that affects shoe fit, other causes may give a shoe a slightly different feel.

Bell says the types of materials, specifically in the upper, can have an impact. “Materials like knit will feel more stretchy than a firm mesh upper, which can change the fit,” she says. “Even the thickness of the tongue and the lacing pattern can provide more, or less, room for your foot. Put this all together and even the same shoe model could feel quite different from one year to the next if these materials change.”

For example, in 2020 New Balance revamped the 1080 with a new, more stretch-friendly knit upper that had enough give to accommodate additional foot shapes. For some runners, it felt roomier than the previous version, but the results were mixed in Runner’s World testing. Sure, the upper material, tongue or lacing doesn’t actually change the true volume of the shoe—and certainly doesn’t impact the length of the silhouette—but the differences in these elements can still impact the overall fit and feel.

One of the biggest questions in the footwear industry centers around fit. Bartold says that individual brands aren’t largely known for having a specific type of fit. “It can vary from season to season, and certainly model to model,” he says. “The truth is that sizing is an absolute mess and a headache. Many of the big companies now have entire departments trying to figure out the size conundrum. It is estimated that about 70 percent of all footwear does not fit true to size based on measurement.”

That’s often simply a testament to the fact that the global footwear industry has three equally powerful fit scales. The United States, United Kingdom and European fit scales all slightly vary, making it extra tricky to get sizing right.

Add in the fact that anatomy averages across the world can differ from region to region and brands may have a tough time finding what works. Bartold says that Salomon, for example, has based its lasts around a French model, which tends to be narrower than an American counterpart. But even that isn’t a “cast iron rule.” He says that within Salomon, the trail shoes tend to run narrower and the road models quite generous.

“It is quite common to find that a particular model from any brand can fit true to size for one season,” he says, “and either bigger or smaller the next.”

Bell says that as brands update models every year or two, no brand categorically runs big or small across the board. “It depends in the model, updates to the last and to the materials used,” she says.

Brands often attempt to tailor a fit to the specific end-use activity. With that philosophy, shoes within the same brand can feel and fit different. “For example, the Nike Vaporfly line offers a snugger fit than the Pegasus, which generally fits true to size,” Bell says. “The Nike Vaporfly is designed for racing, so it offers a performance fit compared to the Pegasus, which is designed for everyday training.”

Even if a brand had gained a reputation for a certain type of fit, that can change with the release of a new model. Bell says Hoka was once known for feeling big and roomy, but the brand’s sizing has dramatically changed and, while their shoes still may be capable of welcoming large feet, now fits truer to size than it once did.

Kris Hartner, owner of Naperville Running Company in Illinois, says it used to be common for brands to vary greatly in size. Now, though, many brands even offer differing widths to accommodate a greater number of foot sizes. “I think lasts are more consistent,” he says. “I think brands have really dialed in and know what shoes fit and what shoes are selling really well.”

Already we’re starting to see a shift toward the more anatomically designed last. “It is a no-brainer that if the shoe is to fit better, the last should be shaped more like a human foot,” Bartold says. “A few companies are doing this now, but only a couple. It is also likely, especially as 3D printing becomes more viable, that companies will have many lasts rather than just one, so footwear recommendations for specific foot-types can be more accurately matched.”

Bartold has clear advice for getting the fit right for you: “Make an appointment with someone who understands fitting properly,” he says.

New scanning machines, such as Volumental located in specialty running stores, can help determine fit, but only if used by someone who understands shoe fitting. Hartner says there’s value to having someone in the know examine a runner’s mechanics, in conjunction with a tool such as Volumental.

The main mistake, according to the experts, is people wear shoes too small for running. Hartner says that statistics show 80 percent of people wear their shoes too small and Bell says most people don’t understand they need about a half size larger in a running shoe than a casual shoe.

Feet have the potential to swell during running and walking. Ensure you have enough room with each step. “You should have a half a size to full size from the end of your longest toe across the toe box of the shoe when standing,” Bell says, “and ensure that your heel is nice and snug back into the shoe.”

“Room in the toe is what you want, to have it fit properly for active use,” Hartner says. “There is a perception you want your forefoot so it doesn’t slide around, but as long as it fits properly in the midfoot, you want to have room in the toe box.”

The length is just one of the important factors to consider. “Foot width and volume matter, as does arch height, foot and ankle movement as you walk or run,” Bell says. “The best thing you can do is get fit by an expert at your local run specialty store.”

Tim Newcomb is a journalist based in the Pacific Northwest. He covers stadiums, sneakers, gear, infrastructure, and more for a variety of publications, including Popular Mechanics. His favorite interviews have included sit-downs with Roger Federer in Switzerland, Kobe Bryant in Los Angeles, and Tinker Hatfield in Portland. 

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