Zero-drop, carbon fiber plates, minimalist or maximalist—runners love to discuss and debate the latest shoe types and features.
Far fewer long-run chats and online forums are dedicated to discussing running shoe size. But how well a shoe matches the length, width, and shape of your feet may actually matter as much as, if not more than, the cushioning that goes underneath them, says Geoffrey Gray, D.P.T., founder and director of research at Heeluxe.
“From a kinetic chain standpoint, your foot is the first point of contact with the ground; your whole skeletal structure is supported by your feet,” says Allison Bowersock, Ph.D., an exercise physiologist and co-owner of RunAbout Sports, a shoe store in Roanoke, Virginia. Here is how to find a shoe that fits—and what can go wrong when you wear one that doesn’t.
How to Find a Running Shoe That Fits
Conventional wisdom holds that your running shoes should be about a size bigger than your dress or casual size. There’s a grain of truth to that—increased blood flow and swelling during and after exercise do make your feet expand, so your running shoes tend to be larger. However, due to sizing variations in all types of shoes, there are too many variables to know exactly how the numbers will align, says Kevin Vincent, M.D., Ph.D., associate professor at the University of Florida and director of the UF Running Medicine Clinic.
So, start with some hard data: If you haven’t had your feet measured since your parents dragged you for school shoes, go for a fitting. The length and width of your feet change due to factors like aging, injuries, and pregnancy.
“The size you wore when you’re 18 might not be the same size you wear when you’re 42, just like you’re probably not wearing the same size pants,” Gray says. “And that’s okay. But we need to get those measurements to know how to change it.” In fact, he recommends getting measured once a year.
Ideally, you’d have this done at a local running-shoe store. People who’ve bought their shoes from a brick-and-mortar establishment seem less prone to poor fit than those who shop online, Gray says.
At RunAbout Sports, the fitting process starts with measuring both feet while you’re standing up. That’s important, because there can be as much as full size-worth of difference between your right and left, Bowersock says. You’ll want a shoe that fits the bigger foot. (You can always change the lacing or add an extra sock on the smaller foot, Vincent says—or, if it’s due to a foot problem like a bunion you haven’t had treatment for, consult with a podiatrist.)
Ideally, a salesperson will bring you several different options. To assess size and fit as you try them on:
- Take the insert out of the shoe and stand on it. The size and shape should match the size and shape of your foot, Vincent says. Your toes shouldn’t spill over the front or sides, and the tip should come to a point roughly where your toes narrow.
- Put the insert back in and put the shoes on. Lace them tightly enough to lock the shoe over your navicular bone—the bony bump over the high point of your arch—or instep, Gray says, but not so tightly that you constrict nerves and blood vessels. You should be able to slide a finger between the knot and your shoe, Vincent says.
- Stand up and check the feel and fit. You want about a thumbnail’s worth of width between your longest toe and the front of the shoe, keeping in mind that your longest toe may be your second metatarsal (the heads of the long toe bones) and not your big toe. As for width, check that there’s little to no pressure on your pinky toe and only slight pressure on your big toe—slightly looser than the snugness of a watch strap on your wrist, Gray says,
- Walk—and, preferably, run. Check that your heel doesn’t slip and that nothing pinches or rubs uncomfortably against your ankle. Also, check the fabric of the upper—if it gathers you might need a snugger fit, and if it bulges or stretches, you might need to go bigger, Bowersock says.
- Repeat until things feel just right. Don’t settle for something cramped thinking you’ll break them in; they should fit properly right from the start, Vincent says. While some parts of the shoe—including the midsole and cushioning—may change for the better with mild wear, that doesn’t affect the sizing or fit, Gray says.
There are exceptions to these rules. For instance, the reason you need extra room in the toes is because most shoes are designed to flex when you run, especially uphill—and that motion brings your toes closer to the end of the shoe. But models with carbon-fiber plates lack this motion, so they can fit more snugly.
“If you’re buying a shoe with different features than what you might be used to—like going from like a trail-running shoe to a major backpacking shoe, or a normal racing flat to a carbon fiber-equipped racing flat—your best size might be different,” Gray says.
Don’t stress if your speciality shop lacks advanced technology, such as foot scanners or fit systems. While they can offer a good baseline for understanding your feet and help standardize the fit process across stores, they’re not yet a substitute for a good shoe-fitter and shouldn’t supersede your experience of how a shoe feels, Gray says.
Instead, worry about one often overlooked detail: your socks. Thick fabric can require you go up as much as a full shoe size to accommodate, Gray says. Try to stick to the same type of socks for each run, and wear them to the store for your fitting. If weather doesn’t permit total consistency—say, you want thicker socks to survive a frigid winter—you might need different size shoe for each season. “It makes a world of difference,” Gray says.