We use UGG USA/UK sizes on our website.
UGG Pre-walker shoes sizes
 USA |  UK |  EU | UGG size | Approximate age |
| 0-1 | 0.5 | 16 | XS | 0-6 month |
| 2-3 | 2 | 18 | S | 6-12 month |
| 4-5 | 4 | 20.5 | M | 12-18 month |
| 6-7 | 6 | 23.5 | L | 18-24 month |
UGG Junior shoe sizes
| USA/UK sizes | EURO size | Approximate Age |
| USA7/ UK 6 | 23.5 | 2-2.5 year |
| USA8/ UK7 | 25 | 2.5-3 year |
| USA9/ UK8 | 26 | 3-3.5 year |
| USA10/ UK9 | 27.5 | 3.5-4 year |
| USA11/ UK10 | 28.5 | 4-4.5 year |
| USA12/ UK 11 | 30 | 4.5-5 year |
| USA13/ UK12 | 31 | 5-6 year |
| USA1/ UK13 | 32.5 | 6-7 year |
| USA2/ UK1 | 33.5 | 7-8 year |
| USA3/ UK2 | 35 | 8-9 year |
| USA4/ UK3 | 36 | 9-10 year |
| USA5/ UK4 | 37 | 10-11 year |
| USA6/ UK5 | 38 | 11-12 year |