How to Buy Kids' Shoes Online: A Size Guide That Actually Works

Children’s shoes are the hardest category to buy online, and the reasons are structural rather than careless. The size scale restarts partway through, different countries restart it at different points, feet grow up to a size every two months in toddlers, and a child cannot reliably tell you a shoe is too tight. I have bought and returned enough kids’ shoes for my own children and for relatives overseas to have a system that works. This is it.

Measure the foot, not the age

Age-based charts are a starting point for gifts, not for a child you can measure. At three years old, foot length ranges from about 150 mm to 175 mm, which spans four US sizes. Measure.

1. Have the child stand on paper against a wall, heel touching the wall, full weight on the foot.
2. Mark the tip of the longest toe. Toddlers curl their toes when they feel a pencil, so distract them and check that the toes are flat.
3. Measure wall to mark in millimeters. Do both feet; use the longer.
4. Measure the widest part of the forefoot too. Young children’s feet are proportionally much wider than adults’.

Do it in the afternoon and keep the number. Then use the kids’ shoe size converter to turn millimeters into the size for whatever country’s store you are buying from. If you only know the child’s age (a gift, a niece abroad), the kids’ size by age page gives the median size with the range, so you can at least buy in the middle.

How much growing room to leave

The rule I use: 8–12 mm of space beyond the longest toe when the shoe is new. That is roughly a thumb’s width in a small shoe and gives about two to three months of growth for a toddler, four to six months for a school-age child.

Less than 6 mm and the shoe will be tight within weeks. More than 15 mm and the child will trip and the shoe flexes in the wrong place, which matters more for kids than for adults because their arches are still forming.

So a child with a 165 mm foot wants an inside length of about 175 mm. On the US scale that is roughly a 10C. Buy 10C, not 11C “to grow into.”

Decoding US C and Y sizes

This is where most overseas parents get lost. The US children’s scale runs:

• 0C to 13C (C = child), covering about 83 mm to 190 mm. Sometimes written 0–13 with no letter, or with “Toddler” for 0–10 and “Little Kid” for 10.5–13.
• 1Y to 7Y (Y = youth), covering about 200 mm to 250 mm. Sometimes “Big Kid” or “Grade School (GS)”.

The scale restarts at 13C → 1Y. A 1Y is bigger than a 13C. After 7Y, the child moves into adult sizing, and a 7Y is the same length as a US men’s 7 or a US women’s 8.5. Nike’s GS range, for example, tops out at 7Y and is often the cheapest way for an adult woman with small feet to buy the same shoe.

The UK uses the same restart but one size lower on the number: UK infant 0–13, then UK junior 1–6. EU and cm do not restart; they count upward continuously, which is why a European store will show a single unbroken scale from 16 to 40.

The conversion chart

Foot lengths are the measured foot, not the shoe. Recommended shoe sizes already include about 10 mm of room.

Foot length	US	UK	EU	cm (JP/KR)	Typical age
105 mm	3C	2.5	18.5	11	6–9 months
120 mm	5C	4.5	21	12.5	12–15 months
135 mm	7C	6.5	23.5	14	18–24 months
150 mm	9C	8.5	26	15.5	2.5–3 years
165 mm	11C	10.5	28.5	17	4 years
180 mm	13C	12.5	31	18.5	5–6 years
195 mm	1.5Y	1	33	20	7 years
210 mm	3Y	2.5	35	21.5	8–9 years
225 mm	4.5Y	4	37	23	10–11 years
240 mm	6Y	5.5	38.5	24.5	12–13 years

Note the EU step is smaller (6.67 mm) than the US step (8.47 mm), so between 13C and 6Y the EU number drifts against the US number by about a size and a half. Always use the converter rather than a fixed offset.

Brand differences that matter for kids

• Nike kids: narrow, especially Air Force 1 and Dunk in GS sizes. For a wide-footed child, go half a size up or choose Adidas. Details on the Nike page.
• Adidas kids: Superstar and Stan Smith run long; a child between sizes should take the smaller. Adidas performance shoes (Duramo, Tensaur) run true. Chart at Adidas sizes.
• New Balance kids: the 574 and 327 come in wide fittings in many markets, and the toe box is roomy. The safest choice for chubby toddler feet. See New Balance sizing.
• Crocs: whole sizes only and run large. Many children fit one size down from their sneaker size.
• Japanese brands (Asics, Mizuno, Moonstar): sizes are exact cm, in 0.5 cm steps, and their kids’ lasts are wide. If you can read the cm, these are the easiest to buy sight unseen.

Buying online without a fitting

Check the store’s return policy before anything else; some overseas sellers do not accept kids’ shoe returns, and shipping a $40 shoe back across the ocean costs more than the shoe. Prefer brands that print cm on the box. Order when you have a fresh measurement, not one from two months ago. And if the child’s foot measures within 3 mm of the top of a size, buy the next size; you will be there in six weeks anyway.

Between sizes with a wide foot, choose the larger size in a brand known to run narrow and the smaller size in a brand known to run wide. That alone fixes most of the fit complaints I hear from parents.

FAQ

What is the difference between 13C and 1Y?

1Y is the next size up from 13C. The US children’s scale counts from 0C to 13C (up to roughly 190 mm), then restarts at 1Y for youth sizes. A 1Y shoe is about 8 mm longer than a 13C.

How often do I need to re-measure my child’s feet?

Every 2 months up to age 3, every 3 months from 3 to 6, and every 4–6 months after that. Growth is not steady; a child can gain a full size in a summer and then nothing for four months. Measuring is faster than guessing.

Can an adult wear youth (Y/GS) sizes?

Yes. A US 7Y equals a US men’s 7 or a US women’s 8.5 in length. Youth versions are usually cheaper and slightly narrower. Women up to about a US women’s 8.5 and men up to a US men’s 7 can buy GS sizes of Nike, Adidas and New Balance.