Most people are wearing the wrong size and don't know it. Feet change—they spread with age, swell over the day, and often aren't even the same size as each other. If you've been buying the size you wore in your twenties, it's worth actually measuring. It takes five minutes and a piece of paper.
Measure at the end of the day
Feet swell as you walk, stand, and warm up. Measure them in the morning and you'll get a size that pinches by evening. Do it late afternoon or evening, wearing the socks you'd actually wear with the shoes. That single timing tip fixes a lot of "these fit in the store but hurt after an hour" complaints.
The paper-and-pen method
Stand on a sheet of paper against a wall, heel touching the wall. Weight on the foot—don't measure sitting, because your foot lengthens under load. Mark the tip of your longest toe (not always the big toe). Then measure heel to mark in centimeters. Do both feet.
For width, measure across the widest part of the foot, the ball, at the same standing load. Width is the measurement most size charts ignore and the one that causes the most misery.
Both feet, and go with the bigger one
It's completely normal for one foot to be up to half a size larger. Always fit to the larger foot—you can pad out a slightly loose shoe on the smaller side, but you can't stretch a too-tight one comfortably.
Turning measurements into a size
Take your longest length in centimeters and match it to the brand's size chart—and here's the key—match it per brand, because a US 9 in one maker runs like a 9.5 in another. Reputable shoe pages list the foot length each size fits. Trust the centimeters over the number on the box.
A rough rule for the toe: you want about a thumb's width (roughly 1–1.5 cm) between your longest toe and the end of the shoe. Zero room means bruised toenails on the downhill; too much means your foot slides and blisters.
Don't forget width and volume
If shoes always feel tight across the ball or leave marks on the sides, you likely need a wide fit, not a longer size—going up in length just makes them long and still narrow. Brands that offer width options (D, E, EE) are worth seeking out if standard shoes never sit right.
Re-measure now and then
Pregnancy, weight change, and simple aging all shift foot size over the years. Re-measure every couple of years, and definitely before a big purchase. When you've got your numbers, check them against the size guide on each product—our listings give the foot length per size so you can match your measurement instead of guessing.