Kids shoe size for two different foot lengths
Many children have one foot slightly longer than the other, and the size always comes from the longer foot.
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How to use it
- Enter left foot length and right foot length.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Take the longer foot, then apply: Last length = foot length + 2/3 in. US child size = 3 × last length (in) − 11.75; Y sizes continue the same scale after 13.5C. UK child size = 3 × last length (in) − 12; UK adult size = 3 × last − 25. EU size = 1.5 × last length (cm), one Paris point being 2/3 cm.
Example
Inputs: Left foot length = 15 cm, Right foot length = 15.4 cm. Result: US size: 8.5C; UK size: 8 (child); EU size: 26.
Limits and caveats
- The last is taken as 2/3 in (about 17 mm) longer than the foot; some European makers add only 13 mm.
- If the gap is more than a full size (about 8.5 mm), ask a foot specialist or a store that sells mixed pairs.
Questions about this tool
Is it normal for a child’s feet to differ?
Yes, a few millimetres is common, which is why both feet are measured.
Why use the longer foot?
A short shoe squeezes the toes, while a little extra room on the other side can be taken up with laces or straps.
How many mm is half a size?
Half a US or UK size is 4.23 mm, and half an EU size is 3.33 mm.