Top down photo of someone having their right foot measured.  You are wearing brown trousers and a black sock and are standing on a very light wooden background.  Another person's hands can be seen holding a yellow tape measure next to the measured foot.

Shoe sizes vary so widely between brands that buying a new pair can feel like a shit shop. Of course, the best way to get a good fit is to just try them on, but that’s not always possible. If you have no choice but to order online, you should know how big your feet actually are in centimeters.

Why centimeters and not inches? Unsurprisingly, they are more common: almost every shoe manufacturer in the world introduces centimeter measurements in their size charts, so once you know your numbers, you can easily find your size on any brand. It also makes converting men’s sizes to women’s or children’s sizes (and vice versa) quick and accurate. Basically, when you buy shoes online, you need to measure your feet.

Fortunately, this is super easy to do. The two best methods require a ruler or tape measure, pen and paper, and someone to help. Centimeter markings are ideal, but it’s fine if you don’t have a metric ruler or tape. Make sure to multiply each measurement in inches by 2.54 to get the corresponding number in centimeters.

It’s easier to use a soft tape measure because you just stand on it and have your assistant calculate the difference in your toe and heel positions. This video from Good Sports Outdoor Outfitters in San Antonio describes the technique in detail:

If all you have is a ruler or something that you don’t want to stand on, you can trace your feet and use it to measure the length. The Michigan Foot Doctors YouTube channel has detailed instructions for correct detection and measurement:

Whichever technique you use, make sure you actually put weight on each foot as you take the measurement so that you get the most accurate number possible. When you’re done, save both measurements to a note on your phone, Google Drive, Dropbox, or password manager. (A post-it on the fridge works too.)

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Using your measurements takes the guesswork out of determining your size. Let’s say your left foot is 10 inches and your right foot is 10 inches. For shoes that need a snug fit and / or are likely to stretch, look for a size that is 26.5 or 27 centimeters. If you want a more roomy fit – for example for boots that you wear with thick socks – choose 27.5 or even 28.

That’s it! You may not get the perfect size every time, but you get a lot closer than traditional number sizes. “Size 9” can mean a million different things, but you can always trust the centimeter.