Last updated: May 2026
Insole sizing is more complex than shoe sizing because most insoles ship in size ranges and require trimming to fit. This guide gives a complete US-EU-UK-CN-JP conversion table for men’s and women’s sizes, explains how to measure your foot accurately, and covers what to do for half sizes, wide widths, and asymmetric feet.
Universal Insole Size Conversion
Insoles are usually sold in size ranges (e.g., M 7-8.5, L 9-10.5) covering 1.5-2 sizes per range. Match your shoe size to the chart below; if you fall on a range boundary, choose the larger size and trim down using the cutting outline.
| US M / W | EU | UK | CN | JP (cm) | Foot length (cm) |
|---|---|---|---|---|---|
| M5 / W6.5 | 38 | 4.5 | 240 | 24.0 | 23.5-23.8 |
| M6 / W7.5 | 39 | 5.5 | 245 | 24.5 | 24.0-24.3 |
| M7 / W8.5 | 40 | 6.5 | 250 | 25.0 | 24.5-24.8 |
| M8 / W9.5 | 41 | 7.5 | 255 | 25.5 | 25.0-25.4 |
| M9 / W10.5 | 42 | 8.5 | 260 | 26.0 | 25.5-25.9 |
| M10 / W11.5 | 43 | 9.5 | 265 | 26.5 | 26.0-26.4 |
| M11 / W12.5 | 44 | 10.5 | 270 | 27.0 | 26.5-27.0 |
| M12 / W13.5 | 45 | 11.5 | 275 | 27.5 | 27.1-27.5 |
| M13 | 46 | 12.5 | 280 | 28.0 | 27.6-28.0 |
How to Measure Your Foot Accurately
Stand on a piece of A4 paper with your full body weight on the foot, mark the heel and longest toe, then measure the distance in centimetres. Measure both feet at end of day (feet swell over the day) and use the larger foot size. A 5 mm or larger difference between feet is common – choose the larger.
- Stand on A4 paper with full body weight
- Mark behind the heel
- Mark in front of the longest toe (often second toe, not big toe)
- Measure heel-to-toe in centimetres
- Repeat for the other foot
- Use the larger measurement, plus 5-7 mm clearance, for shoe size
Half Sizes and Trimming
Most insoles are designed to be trimmed at the toe outline. Use sharp scissors and cut along the printed line for your shoe size, removing a 2-5 mm strip. Always test-fit before trimming aggressively – too short an insole shifts in the shoe and causes blisters.
- Use sharp scissors, not a craft knife
- Cut along the printed outline only – never trim heel or arch
- Trim 2-5 mm at a time, test-fit between cuts
- If unsure, leave 2 mm extra; insoles compress slightly with wear
Wide and Narrow Foot Considerations
Wide-footed users (wider than 10 cm at the metatarsal heads for men, 9 cm for women) should choose insoles labelled wide-fit or trim the medial and lateral edges with a craft knife to relieve pressure. Narrow-footed users typically size the insole correctly without modification but may notice forefoot slip in wide shoes.
Asymmetric Feet (Different Sizes Left vs Right)
5-10 mm difference between feet is common (1 in 5 adults). Buy two pairs of insoles in different sizes if the difference is large; for smaller differences, size to the larger foot and add a thin heel pad to the smaller foot. Custom 3D-scan insoles handle asymmetry natively.
Frequently Asked Questions
What size insole do I need?
Match your shoe size to the standard conversion chart, then choose insole size accordingly. If you fall between ranges, size up and trim down using the printed outline.
Is insole size the same as shoe size?
Insoles are sold in size ranges (e.g., M 7-8.5) covering 1.5-2 shoe sizes per range. Most insoles need to be trimmed to fit your specific shoe size within the range.
How do I trim an insole to size?
Use sharp scissors and cut along the printed size line at the toe end. Trim 2-5 mm at a time and test-fit between cuts. Never trim the heel or arch portions of the insole.
What if my left and right feet are different sizes?
5-10 mm difference is common. For small differences, size to the larger foot and add a thin heel pad to the smaller. For 10+ mm differences, buy two separate pairs in different sizes or invest in custom 3D-scanned insoles.
How do I convert between US, EU, and UK shoe sizes for insoles?
Use the conversion chart in this guide. US M9 = EU 42 = UK 8.5 = CN 260 = JP 26.0 cm. Women’s sizes typically run 1.5 sizes higher than men’s in US (M7 = W8.5).
Should I size up or size down for insoles?
Always size up. A slightly oversized insole can be trimmed down; an undersized one cannot be made larger and will shift in the shoe.
Do half-size shoes need half-size insoles?
Most insole brands cover half sizes within their size ranges (e.g., M 7-8.5 covers 7, 7.5, 8, 8.5). Trim along the outline to fit your specific size.
What about kids’ insole sizes?
Kids’ insole sizing follows the same conversion logic but with smaller ranges (e.g., 1-2.5, 3-4.5). Children’s foot growth is rapid – replace insoles every 4-6 months or as soon as the toes reach the trim line.