Quick Answer: Feet swell through the day and can gain 4-8% in volume by evening, which is often more than a half size in fit. Shop in the late afternoon or after activity, not first thing, and fit to the larger foot. A shoe that fits perfectly at 9am is usually too small by 5pm.

This explains something most people have experienced and never resolved: shoes that were comfortable in the shop and are not comfortable at the end of a long day. It usually isn’t the shoe. It’s when you tried it.

How much do feet actually change in a day?

Measurably. Foot volume typically increases 4-8% from morning to evening in healthy adults, driven by fluid pooling from gravity, activity, and temperature.

In practical shoe terms, that’s often the difference between a comfortable fit and a tight one, and in some people it crosses a half size. It’s larger after a long flight, after standing for hours, in warm weather, and with higher sodium intake.

There’s also a shorter-term effect from activity. Feet expand during running and walking as blood flow increases, which is why runners are routinely advised to size up by a half size relative to their casual shoes. That’s not about running shoes being cut smaller; it’s about the foot being bigger while running.

So the honest answer to what size are you is: it depends on when you ask.

When should you actually buy shoes?

Late afternoon or early evening, after you’ve been on your feet. That’s the larger end of your daily range, and it’s the state your shoes need to accommodate.

Even better, if you’re buying athletic shoes: try them after a walk or a workout, when your feet are at their most expanded. It feels excessive and it’s the closest approximation of the conditions the shoe will actually work in.

What to avoid is the common pattern of trying shoes first thing on a weekend morning, when your feet are at their smallest and least swollen. Shoes bought that way fit for about four hours a day.

One caveat worth stating: don’t overcorrect. Buying for maximum evening swelling can leave a shoe sloppy in the morning, which causes its own problems with rubbing and blistering. The right target is a shoe that’s comfortable at your evening size with the laces adjusted, and snug but not tight in the morning.

How to check fit properly

Thumb width at the toe. About 3/8 to 1/2 inch between your longest toe and the end of the shoe, checked standing, not sitting. Your longest toe isn’t necessarily your big toe.

Width at the ball, not the toes. The widest part of your foot should sit at the widest part of the shoe. If it doesn’t, it’s the wrong last shape and no size will fix it.

Heel lock. Walk and feel for slip. A little movement is normal; noticeable lift means either the wrong size or the wrong shape.

Both feet, standing. Most people have a measurably larger foot, often by a half size. Fit the larger one and adjust the smaller with lacing or an insole.

With the socks you’ll wear. Especially into fall, when sock thickness changes. A sneaker fitted with a thin summer sock is a different shoe with a wool sock in November.

Myth vs Fact: sneaker fit

Myth: Your shoe size is fixed once you’re an adult.

Fact: Feet lengthen and widen over decades as connective tissue relaxes, and pregnancy can permanently change size. Measure every couple of years rather than assuming.

Myth: Sneakers stretch to fit.

Fact: Uppers give slightly, particularly knits and leathers. Length essentially doesn’t change, because the sole doesn’t stretch. A shoe that’s short stays short.

Myth: Both feet are the same size.

Fact: Around 60% of people have a noticeable difference between feet. Fit the larger.

Myth: Size is consistent across brands.

Fact: Lasts vary substantially between brands and even between models within a brand. Your size is a starting guess every single time.

What changes about sneaker fit in fall?

Socks, mostly, and it’s a bigger change than it seems. Moving from a thin no-show to a mid-weight crew sock can take up 2-3mm of internal volume, which is enough to turn a well-fitted shoe tight.

Temperature matters too. Feet swell less in cool weather, so a shoe bought in August at peak swelling can feel roomy in November. That’s usually fine and easily managed with lacing, but it’s worth knowing before you conclude the shoe stretched out.

And if you’re buying boots or shoes now for winter, size for the thickest sock you’ll wear with them. This is the single most common winter footwear mistake: fitting in the shop with the sock you wore that day rather than the one you’ll wear in January.

A practical move: keep the socks you actually wear with athletic shoes in your bag when shoe shopping in the shoulder seasons.

FAQ: Sneaker Fit Questions, Answered

Should running shoes really be a half size up?

Usually yes, versus your casual size, because feet expand during running and repeated downhill impact pushes toes forward. Check for thumb-width clearance while standing.

What if I’m between sizes?

Generally go up and manage the fit with lacing and an insole, since you can take up volume but you can’t add length.

Are my feet swelling too much?

Normal daily swelling is symmetrical and resolves overnight. Swelling that’s one-sided, doesn’t resolve by morning, or comes with pain is worth taking to a professional rather than fixing with shoes. This is general information, not medical advice.

TL;DR:

• Feet gain 4-8% in volume through the day, which can exceed a half size in fit terms.
• Shop in the late afternoon or after activity, and fit to your larger foot standing up.
• Check thumb-width clearance, ball width alignment, and heel lock, with the socks you’ll actually wear.
• Fitting for winter means fitting with a winter sock, not the one you have on today.

Most of the sneakers people describe as broken in badly were simply fitted at 9am. Try the next pair at 5pm and you’ll notice the difference before you leave the shop.