To measure an insole, you need a flexible tape measure and the shoe you want to fit. The most reliable method is measuring inside the shoe itself, from the tip of the toe box to the back of the heel, with the tape lying flat against the bottom. This gives you the true insole length in centimeters, which you can then match to sizing charts or use when ordering replacements.
Measuring Length Inside the Shoe
Start with a pair of shoes that fits you well. Remove the existing insole if there is one. Take a flexible tape measure (or a piece of ribbon you can mark and measure afterward) and push the zero end all the way into the tip of the toe box. Walk the tape flat along the bottom of the shoe until it reaches the inside of the heel. Read the measurement in centimeters.
If your measurement lands between half sizes, round up to the nearest half size. For example, 18.25 cm rounds up to 18.5 cm. This small buffer prevents the insole from bunching or curling inside the shoe.
If you still have the original insole, you can also pull it out and measure it directly on a flat surface. Place the tape from the very back of the heel to the furthest point at the toe. This approach is faster, but measuring inside the shoe tends to be more accurate because insoles can warp or shrink slightly after months of use.
Measuring Width
For width, find the widest part of the insole or shoe interior, which sits across the ball of the foot. This is roughly where your big toe joint and little toe joint would press outward. Lay the tape straight across that point and record the measurement. Width matters most when you’re buying rigid or semi-rigid insoles that won’t flex to fit, since a too-wide insole will buckle and a too-narrow one won’t support the outer edge of your foot.
Converting Centimeters to Shoe Sizes
Once you have your centimeter measurement, you can cross-reference it with standard sizing. Here are some common reference points:
- Women’s US 7: 23.5 cm
- Women’s US 9: 25.1 cm
- Men’s US 9: 26.0 cm
- Men’s US 10: 27.0 cm
- Men’s US 12: 28.6 cm
Keep in mind that brands vary slightly. A US men’s 10 from one manufacturer might measure 27.0 cm while another comes in at 27.3 cm. Your tape measure measurement is always more reliable than the number printed on the shoe.
Choosing the Right Insole Volume
Length and width aren’t the only dimensions that matter. Insole thickness, often called “volume,” determines whether the insole will actually fit inside your shoe without making it too tight.
Thin insoles work best in tight-fitting footwear like dress shoes, cleats, or performance flats. Medium-volume insoles suit shoes that already fit comfortably, such as running shoes or casual sneakers, especially if you can remove the factory liner first. Thick or “max” volume insoles are designed for footwear with extra interior space: work boots, hiking boots, or waders.
A simple test: pull out the existing insole, stand on the new one inside the shoe, and check that your foot doesn’t feel squeezed at the top. If it does, you need a thinner profile.
How to Trim an Insole to Fit
Many insoles are sold as “trim to fit,” meaning they come slightly oversized with guidelines printed on the bottom. The safest way to trim them is to use your old insole as a template. Place the old insole on top of the new one and align them at the heel, not the toe. This keeps the arch support in the correct position relative to your foot. Trace the outline of the old insole with a pen, then cut along the line with sharp scissors.
Cut conservatively. You can always trim more off, but you can’t add material back. After cutting, drop the new insole into the shoe and press it flat to make sure it lies without any edges folding up against the sides.
Account for Material Compression
Insoles compress over time, and the rate depends on the material. The two most common materials are EVA foam and polyurethane (PU).
EVA is lighter and softer out of the box. It compresses roughly 12% after about 300 miles of use and loses around 15% of its cushioning after extended testing. After 1,000 compression cycles, EVA retains about 92% of its original shape, but with continued daily wear, it noticeably thins out over months.
PU is denser and more durable. It compresses only about 6% over the same 300 miles and retains 93% of its shock absorption capacity under heavy load testing. It holds up better long-term but feels firmer underfoot. If you’re measuring a well-worn EVA insole to find a replacement, your old insole may be thinner than it was originally. Factor in that difference, or measure a newer shoe with a similar fit for a more accurate baseline.
Measuring Your Foot Directly
If you don’t have a well-fitting shoe to work from, you can measure your foot on paper. Stand on a sheet of paper with your full weight on the foot (sitting measurements run shorter). Trace around your foot with a pen held vertically. Measure from the back of the heel mark to the longest toe, then across the widest point of the ball. Add about 0.5 cm to the length for breathing room, since insoles sit inside a shoe that extends slightly beyond your foot in both directions.
Do this at the end of the day. Feet swell throughout the day and can be a full size larger by evening compared to morning. Measuring when your feet are at their largest ensures the insole won’t feel tight during your most active hours.