Children's Shoe Size Converter

US, UK, EU and Japanese children’s shoe sizes from the one thing that means anything — the foot length in millimetres. The US number restarts at 13½C → 1Y and the UK number at 13½ → 1, three published charts disagree about the US scale by up to a full size, and growing room is already inside every chart you will read. All of that is on this page.

Last updated 24 Sep 2026

Children's shoe sizes

Foot length → four scales

What have you got?Measuring beats every chart. Stand the child on paper against a wall, in the evening, with weight on the foot; mark the longest toe on both feet and use the larger.

The size, or the lengthRead in whatever the box above says — millimetres, centimetres, or a size number.

Growing room (mm)How much longer the shoe is than the foot. Clarks’ own fitting guide asks for 14 mm at the longest toe, 10 mm for sandals and pre-walkers; a US retailer’s “half an inch or a little more” is 12.7 mm. This is the single biggest source of disagreement between charts, so it is a control here rather than a hidden constant.

Which US children’s chart?Three published families, a quarter, a half and a full size apart. The retail one is the default because it is the only one that makes 13½C and 1Y the same length.

Not a circuit: a foot drawn inside a shoe, both to the SAME scale, which is the whole argument of the page in one picture. The shoe is drawn at a constant length, so the gap at the toe shows what fraction of the shoe your growing-room allowance is taking up — raise the allowance and the foot shrinks back from the toe. The upper dimension is the growing room, the lower pair are the foot and the shoe's inside length. A published size chart already contains a gap like this one, which is why you enter the foot and not the foot plus a thumb's width.

182.0mmExample

a 168 mm foot with 14 mm of growing room

One measurement, four ladders, two restarts

shoe length = foot length + growing room · UK child = 3 × shoe (in) − 12 · UK adult = UK child − 13 · US child = UK child + ½ (retail) · US youth Y = US child − 13 · EU = 1.5 × shoe (cm) · Japan = foot (cm) · Mondopoint = foot (mm)

barleycorn: ⅓ inch, 8.47 mm — one full UK or US size, in both the children’s and the adult scale
Paris point: ⅔ cm, 6.67 mm — one full EU size, so EU steps are smaller and the EU number climbs faster than the UK one
growing room: how much longer the shoe is than the foot. Published figures run 10 to 17 mm; this page opens at Clarks’ 14
− 13: the label restart. UK child 14 and UK adult 1 are the same shoe; so are US 13½C and 1Y on the retail family
Mondopoint: ISO 9407: the size IS the foot length in millimetres, in 5 mm steps. Nothing to convert

Worked example

a 168 mm foot with 14 mm of growing room
The shoe has to be longer than the foot by the growing room: 168 + 14 = 182.0 mm inside length
That is 7.165 in, so the UK children's number is 3 × 7.165 − 12 = 9.50 — a UK 9½
The retail US charts add half a size: 10.00, a US 10C. Wikipedia's formula would make it 9.75 and REI's chart a 10½
The EU number is 1.5 × 18.2 cm = 27.30, so EU 27
Japan and the centimetre scale print the FOOT, not the shoe: 16.8 cm. Mondopoint rounds the same foot to 170 mm
None of this is a restart yet — at UK 9.5 we are still four and a half sizes below the point where the label starts again at 1

The whole ladder at a 14 mm allowance, with the labels as they are printed

Two columns go blank halfway down and two start: that is the label restart, and it is the whole difficulty with children’s sizes. The UK number runs to 13½ and then starts again at 1; the US number runs to 13½C and then starts again at 1Y. Neither restart is a step in the ladder — the foot lengths keep going up by a barleycorn each time. EU and Japanese numbers do not restart at all, which is the single best reason to shop in them. Built from the formulas below, not copied from a chart.
Foot (cm)	Shoe inside (mm)	UK child	UK adult	US child (C)	US youth (Y)	EU	Japan / cm	Mondopoint (mm)
10.5	119	2	—	2½C	—	18	10.5	105
11.5	129	3	—	3½C	—	19	11.5	115
12.5	139	4½	—	5C	—	21	12.5	125
13.5	149	5½	—	6C	—	22	13.5	135
14.5	159	7	—	7½C	—	24	14.5	145
15.5	169	8	—	8½C	—	25	15.5	155
16.5	179	9	—	9½C	—	27	16.5	165
17.5	189	10½	—	11C	—	28	17.5	175
18.5	199	11½	—	12C	—	30	18.5	185
19.5	209	12½	—	13C	—	31	19.5	195
20.5	219	—	1	—	1½Y	33	20.5	205
21.5	229	—	2	—	2½Y	34	21.5	215
22.5	239	—	3	—	3½Y	36	22.5	225
23.5	249	—	4½	—	5Y	37	23.5	235
24.5	259	—	5½	—	6Y	39	24.5	245

The US children’s number: three published answers

These are the raw ladder values, before anyone rounds them to the nearest half size, which is the only way to see that the disagreement is structural. The three published families sit a fixed quarter, half and full size above the UK number at EVERY length, so the spread between the extremes is three quarters of a size everywhere — and after rounding that becomes a whole size at many of them. The retail family is the default here for a reason that can be checked: only with US = UK + ½ does a 13½C come out the same last length as a 1Y, which is what every chart prints as consecutive. On Wikipedia’s constant a 13½C is a quarter of a size LONGER than a 1Y, so the two labels overlap and the ladder cannot be printed as one.
Foot (cm)	UK child	US, retail charts (+½)	US, Wikipedia (+¼)	US, REI (+1)	Spread between the extremes
12.0	3.83	4.33	4.08	4.83	0.75
13.0	5.01	5.51	5.26	6.01	0.75
14.0	6.19	6.69	6.44	7.19	0.75
15.0	7.37	7.87	7.62	8.37	0.75
16.0	8.55	9.05	8.80	9.55	0.75
17.0	9.73	10.23	9.98	10.73	0.75
18.0	10.91	11.41	11.16	11.91	0.75
19.0	12.09	12.59	12.34	13.09	0.75
20.0	13.28	13.78	13.53	14.28	0.75
21.0	14.46	14.96	14.71	15.46	0.75
22.0	15.64	16.14	15.89	16.64	0.75

Clarks’ published chart, and the growing room hidden inside it

The last two columns are computed, not copied: they are the gap between the foot length Clarks prints and the shoe length its UK and EU numbers stand for. Both average about 9.7 mm — and Clarks’ own fitting guide asks for 14 mm at the longest toe. Those are not the same quantity (a last length is not free space at the toe) but they are not the same number either, and the chart’s UK column swings from 7.1 to 13.9 mm with no pattern, which is what a table looks like when it is not generated from a formula. A Clarks stockist states the consequence plainly: the chart “will allow for between 10mm – 15mm of growing room. You do not have to add the growing room onto the foot length.”
UK, as printed	EU	Foot (cm)	Age band Clarks gives	Allowance its UK number implies (mm)	… and its EU number (mm)
2½	18	11.0	6–9 mths	12.8	10.0
3	19	11.7	9–12 mths	10.0	9.7
4	20	12.4	12–18 mths	11.5	9.3
5	21	13.0	18–24 mths	13.9	10.0
5½	22	13.7	2 yrs	11.2	9.7
6½	23	14.4	2–2½ yrs	12.6	9.3
7	24	15.0	2½–3 yrs	10.9	10.0
7½	25	15.7	3 yrs	8.1	9.7
8½	26	16.4	3½ yrs	9.6	9.3
9	27	17.0	4 yrs	7.8	10.0
10	28	17.7	4½ yrs	9.3	9.7
11	29	18.4	5 yrs	10.7	9.3
12	30	19.0	5–6 yrs	13.2	10.0
12½	31	19.7	6 yrs	10.4	9.7
13	32	20.4	6–7 yrs	7.7	9.3
1 (adult)	33	21.0	7–8 yrs	10.1	10.0
2	34	21.7	8–9 yrs	11.6	9.7
2½	35	22.4	9–10 yrs	8.8	9.3
3	36	23.0	10–11 yrs	7.1	10.0
4	37	23.7	11–12 yrs	8.5	9.7
5	38	24.4	12–13 yrs	10.0	9.3
6	39	25.0	13–14 yrs	12.5	10.0

Mean foot length by age — a population figure, not a target

From 2,745 Croatian children measured by Vrdoljak, Kujundžić Tiljak and Cimić (2017). Read the last column before the others: two standard deviations is about 2.2 cm, which is two and a half UK sizes, so a perfectly ordinary five-year-old can be two sizes either side of the mean. This table is for sanity-checking a measurement you already took, never for buying shoes from an age. The same paper gives the growth rate: about 1.8 cm in a girl’s third year, 1.6 cm in a boy’s, and then “about 1cm yearly” from three to six — which is why 14 mm of room is roughly one year of it, and why under-threes need re-measuring far more often.
Age (yrs)	Girls (cm)	Boys (cm)	UK size the mean lands on	EU size	Two SDs of girls’ spread (cm)
2	13.55 ± 1.06	14.16 ± 1.09	6	23	2.12
3	15.36 ± 1.13	15.74 ± 1.22	8	25	2.26
4	16.65 ± 1.08	16.87 ± 1.07	9½	27	2.16
5	17.76 ± 1.09	18.00 ± 1.04	11	29	2.18
6	18.89 ± 1.09	19.09 ± 1.32	12	31	2.18
7	19.66 ± 1.21	19.95 ± 1.43	13	32	2.42

Growing room: what each publisher actually says

Six published figures spanning 10 to 17 mm, which is a full UK size of disagreement (a barleycorn is 8.47 mm). That is why the allowance is an input on this page and not a constant. Two of them are thresholds rather than targets: buy at 17 mm, replace at 12.
Source	What it says	In mm	In inches
Clarks, Check the Fit	“Ensure 14 mm from the longest toe”	14	0.55
Clarks, sandals and pre-walkers	“10 mm for sandals/pre-walking styles”	10	0.39
Little Treads (Clarks stockist)	the chart already allows 10–15 mm; do not add it again	10–15	0.39–0.59
blitzresults, replace at	“less than a half-inch (12mm) of space … time for a new pair”	12	0.47
blitzresults, buy at	“new shoes should provide at least 3/4 inch (17mm)”	17	0.67
REI	“about a half an inch or a little more”	12.7	0.50

The number restarts, and the growing room is already in the chart

Children’s shoe sizes are the worst-behaved scale on this site, and they are badly behaved in a specific, learnable way: the number restarts. A UK children’s size climbs from about 0 to 13½ and then starts again at 1 as an adult size. A US children’s size climbs to 13½C and then starts again at 1Y. Neither restart is a step in the shoe — the foot lengths keep rising by a barleycorn, 8.47 mm, each half-size — but if you compare a 13 with a 1 you will be thirteen sizes out instead of half a size. EU and Japanese numbers never restart, which is a good enough reason to shop in them.

Only one number here is a measurement. The Japanese size is the foot length in centimetres and Mondopoint (ISO 9407) is the foot length in millimetres; both are identities, not conversions. Everything else is a convention laid over the length of the shoe’s last: UK = 3 × last in inches − 12 for children, EU = 1.5 × last in centimetres. Because the UK step is a third of an inch and the EU step two thirds of a centimetre, the two ladders climb at different rates and the gap between the numbers widens as the foot grows. That is visible in Clarks’ own chart, where the EU number is fifteen and a half above the UK one at the bottom and twenty above it at the top.

The US children’s constant is genuinely disputed, and the three answers are a quarter, a half and a full size apart. Retail charts — Clarks’ stockists, blitzresults, Nike — put the US number half a size above the UK one. Wikipedia’s closed-form barleycorn formula puts it a quarter above. REI’s whole-size chart puts it a full size above. This page prints all three and defaults to the retail one, for a reason you can check in the table: only with US = UK + ½ does a 13½C come out exactly the same length as a 1Y, which is what every chart prints as consecutive. On the other constants the two labels overlap.

Growing room is the question people are really asking, and it is the biggest single source of error. A shoe has to be longer than the foot, and published figures for how much run from 10 to 17 mm — more than a full size of disagreement. Clarks asks for 14 mm at the longest toe (10 mm for sandals and pre-walkers); a US retailer says half an inch; blitzresults frames it as thresholds, buy at 17 mm and replace below 12. The trap is double-counting. A published size chart has the allowance already in it. Working backwards through Clarks’ chart, its own numbers embed about 10 mm, and a Clarks stockist states it outright: “You do not have to add the growing room onto the foot length.” So measure the foot, enter the foot, and let one allowance be applied once. Add a thumb’s width on top of a chart and you have bought a size too big.

Measure, do not guess from an age. The by-age table on this page is a population mean from 2,745 measured children, and two standard deviations of it is about two and a half UK sizes — so an entirely ordinary child can sit two sizes either side of the average for their year. A foot off the mean is not a problem; it is the mean. What the same study is genuinely useful for is the growth rate: about 1.6 to 1.8 cm in the third year and about 1 cm a year from three to six. Fourteen millimetres of room is therefore roughly one year of growth above three, and rather less than that below it, which is the honest basis for how often to re-measure. For the adult scales see the shoe size converter; for the other body scales that work this way, a convention on top of a measurement, see the clothing size converter and the hat size converter.

Frequently asked questions

Why do US children’s shoe sizes start at 1 twice?

Because the scale is relabelled rather than continued. The US children’s number climbs from about 0 to 13½, and then the next size up is printed 1Y — the youth scale, which is the same ladder as men’s 1. So a 13½C and a 1Y are next to each other on the shelf even though one says 13 and the other says 1. Before that there is a second, softer break in the marketing: ‘toddler’ or C sizes up to about 9½C or 10C, ‘little kid’ and ‘big kid’ above. The C/Y break is real and dimensional; the toddler/little-kid break is only a category.

Is a US 13.5C the same length as a 1Y?

On the retail charts, yes, exactly — and that is why those charts use the constant they use. With US = UK + ½ both labels land on a shoe 8.333 in long. On Wikipedia’s formula (US = UK + ¼) they do not: a 13½C comes out a quarter of a size longer than a 1Y, so the two labels overlap. This page lets you pick which family to use and shows what each one gives.

Do UK children’s sizes carry on into adult sizes?

The ladder does; the label does not. UK sizing is one unbroken run of barleycorns from a baby’s foot to an adult’s — there is no step and no overlap — but the number is reset once, after 13½, and starts again at 1. UK child 14 and UK adult 1 are the same shoe, which is why the arithmetic here is simply UK adult = UK child − 13. EU and Japanese sizes do not reset at all.

Does a chart’s size already include growing room?

Almost always yes, and you should not add it twice. A Clarks stockist says so in terms: the chart “will allow for between 10mm – 15mm of growing room. You do not have to add the growing room onto the foot length.” Working backwards through Clarks’ own published chart, its numbers embed about 10 mm. Enter the measured foot and let the page or the chart add the room; if you add a thumb’s width yourself as well you will buy shoes a full size too big.

How much growing room should a child’s shoe have?

Published figures run from 10 to 17 mm and the difference is a full size, so there is no single answer. Clarks asks for 14 mm at the longest toe and 10 mm for sandals and pre-walkers; a US retailer says “about a half an inch”, which is 12.7 mm; blitzresults frames it as thresholds — buy with at least 17 mm, replace below 12. Between three and six a foot grows about 10 mm a year, so 14 mm is roughly a year of wear.

How often should I re-measure?

Whenever you buy, and between times as often as the growth rate makes sense of. Under three the foot gains about 1.6 to 1.8 cm a year — two full sizes — so a couple of months can matter. From three to six it is about 1 cm a year, so a check every three or four months is enough, and a US retailer’s advice of “a couple times a year” is reasonable above that. Measure both feet and fit the larger.

Is a Japanese children’s size really just the foot length?

Yes. Japanese sizing is the foot length in centimetres, in 5 mm steps, and Mondopoint (ISO 9407) is the same idea in millimetres. That makes them identities rather than conversions — there is no hidden allowance and nothing to get wrong. Japanese and Mondopoint sizes also carry a width or girth letter, which this page does not convert.

What about width fittings — F, G, H?

This page does not convert them, deliberately. UK width letters are Clarks’ own system, not a standard, and they do not transfer to another maker or to EU or US sizing at all; a US ‘wide’ and a Clarks G are not the same fitting and no arithmetic relates them. Width also interacts with length: a wide foot in a too-narrow shoe reads as needing a longer size. If width is the problem, it has to be measured on a maker’s own gauge.

Related calculators

References

Clarks, Check the Fit (clarks.com/en-gb/check-the-fit, read 27 September 2026), the maker’s own fitting rule and the default this page opens with: “Ensure 14 mm from the longest toe (10 mm for sandals/pre-walking styles)”.
Clarks’ children’s size chart as republished with Clarks branding by The Golden Boot (thegoldenboot.co.uk/clarks-size-and-fit-guide, read 27 September 2026): UK label, EU size, foot length in centimetres and the age band, from UK 2½ at 11.0 cm to UK 6 at 25.0 cm. Its length column is the FOOT, not the shoe. A second Clarks stockist, Little Treads (littletreads.com.au, read 27 September 2026), states what that means in terms: the chart “will allow for between 10mm – 15mm of growing room. You do not have to add the growing room onto the foot length.”
blitzresults.com, Kids’ Shoe Size Chart (read 27 September 2026), the second published family and the one that carries a US column. Its three tables split exactly where the US label restarts — toddler US 4½C to 9½C, kids US 10C to 13½C, youth US 1Y to 6Y — and its US number sits half a size above the UK number at every row. It also gives the replace-and-buy rule in millimetres: under 12 mm of room means a new pair, and a new pair should start with at least 17 mm.
REI, Understanding Kids’ Shoe Sizes (rei.com, read 27 September 2026), the third published family: whole US sizes only, and its UK column is a FULL size below the US number rather than half a size. It confirms the break — “Size 13 Kids’ (toddlers) is followed by size 1 Kids’ (big kids)” — and gives the allowance as “about a half an inch or a little more”, with a fit check “a couple times a year”.
Wikipedia, Shoe size (read 27 September 2026), for the barleycorn ladders in closed form: UK adult = 3 × foot (in) − 23, UK child = 3 × foot − 10, US men = 3 × foot − 22 and US child = 3 × foot − 9¾, with the UK children’s scale ending at 13½ and “the adult scale then start[ing] at size 1”. Its US children’s constant is a quarter of a size away from the retail charts’, which is why this page prints both.
M. Vrdoljak, M. Kujundžić Tiljak and O. Cimić, Anthropometric measurements of foot length and shape in children 2 to 7 years of age, Periodicum Biologorum 119(2), 2017 — 2,745 Croatian children, 5,490 feet. The source of the by-age table here, which is a population mean with its standard deviation and not a target. Its own finding on growth rate: “The foot grows fastest in length between ages 2-3 – by 1.8cm in girls and 1.6cm in boys. From the 3rd to 6th year, the foot grows rather uniformly, by about 1cm yearly.”
ISO 9407, Footwear — Sizing — Mondopoint system of sizing and marking, and JIS S 5037, Sizing systems and marking for shoes. Both are copyrighted and neither was fetched; they are cited by number for the one fact this page uses from them, that a Mondopoint or Japanese size IS the foot length (in millimetres and centimetres respectively). That is an identity, not a conversion, and the adult shoe size converter says the same.

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