Frequently Asked Questions
Everything you need to know about finding your shoe size.
Our calculator is built on the Brannock Device — the metal foot-measuring tool you’ve stood on at shoe stores for decades. Invented in 1925, it’s still the industry standard nearly every shoe brand uses to define their size charts, measuring both foot length and width (ball width) at once. That’s why entering your length and width gives you a size that lines up with how brands actually built their shoes, rather than a rough estimate.
A Brannock Device tells you a size — full stop. Ours goes a step further: you get the actual millimeter measurement behind that size, so there’s no guessing involved. We also show you exactly where you fall within that size’s range, so if you’re near the edge, you’ll know whether it makes sense to size up or down before you buy.
Our size calculator shows all three conversions alongside the Japanese cm sizing. US and UK differ by about 0.5 sizes; EU roughly follows a different scale. When in doubt, go by actual foot length in mm.
A good rule of thumb is roughly a half inch — or about a thumbnail’s length — of space between your longest toe and the end of the shoe. This gives your foot room to move naturally without the shoe being so large it causes heel slip. For a precise measurement, use the calculator above.
Heel slip is when your heel moves up and down inside the shoe as you walk or run. Beyond being annoying, it can cause blisters and, over time, contribute to injury. The most common causes are an improper shoe size or lacing technique. For an accurate fit, use the calculator above.
Mid-afternoon to early evening. Your feet naturally swell throughout the day due to gravity, blood flow, and the cumulative effect of standing and walking — sometimes up to a half size larger by day’s end. Trying on shoes during this window ensures you’re fitting for your foot at its largest, so your shoes are comfortable all day long. Our size calculator can help you estimate your length and width from a simple measurement.
No. There’s no account and no database here — the calculator runs entirely in your browser, and the length and width you type in are never sent to our servers or stored anywhere. See our Privacy Policy for the full picture.
Every brand builds their size chart off the same Brannock standard, but that’s where the consistency ends. Materials, stitching patterns, and — most of all — the “last” (the foot-shaped mold a shoe is built around) all vary from brand to brand and even model to model. That’s why a size 9 in one shoe can fit differently than a size 9 in another, even though both are technically “correct.”
Take those measurements to FindMyRunningShoes and use your new size and width to shop shoes that are actually in stock in your fit. Their AI-powered fit tool goes a step further too, matching shoes to how you move, not just your measurements.
Head over to FindMyRunningShoes — our sister site — and use your new size and width to shop shoes that are actually in stock in your fit. Their AI-powered fit tool goes a step further too, matching shoes to how you move, not just your measurements.