All womens shoes are done in US sizing
Women's Shoe Size Chart
| US | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| UK | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| EU | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 |
| US | UK | EU |
| 5 | 3 | 36 |
| 6 | 4 | 37 |
| 7 | 5 | 38 |
| 8 | 6 | 39 |
| 9 | 7 | 40 |
| 10 | 8 | 41 |
| 11 | 9 | 42 |
| 12 | 10 | 43 |
Women's Slipper Size Chart
| US | 5-6 | 7-8 | 8-9 | 9-10 |
| S-XL | S | M | L | XL |
All men's shoes sold by Number One Shoes are UK sizes.
Men's Shoe Size Chart
| US | 6.5 | 7.5 | 8.5 | 9.5 | 10.5 | 11.5 | 12.5 | 13.5 | 14.5 |
| UK | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
| EU | 39.5 | 41 | 42 | 43 | 44 | 45 | 46.5 | 48.5 | 49.5 |
| US | UK | EU |
| 6.5 | 6 | 39.5 |
| 7.5 | 7 | 41 |
| 8.5 | 8 | 42 |
| 9.5 | 9 | 43 |
| 10.5 | 10 | 44 |
| 11.5 | 11 | 45 |
| 12.5 | 12 | 46.5 |
| 13.5 | 13 | 48.5 |
| 14.5 | 14 | 49.5 |
Men's Slipper Size Chart
| US | 7-8 | 8-9 | 10-11 | 12-13 |
| S-XL | S | M | L | XL |
All kids' shoes sold by Number One Shoes are UK sizes.
Kid's Shoe Size Chart
| US | 11 | 12 | 13 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| UK | 10 | 11 | 12 | 13 | 1L | 2L | 3L | 4L | 5L | 6L |
| EU | 27.5 | 28.5 | 29.5 | 30.5 | 32.5 | 33.5 | 34.5 | 35.5 | 36.5 | 37.5 |
| US | UK | EU |
| 11 | 10 | 27.5 |
| 12 | 11 | 28.5 |
| 13 | 12 | 29.5 |
| 1 | 13 | 30.5 |
| 2 | 1L | 32.5 |
| 3 | 2L | 33.5 |
| 4 | 3L | 34.5 |
| 5 | 4L | 35.5 |
| 6 | 5L | 36.5 |
| 7 | 6L | 37.5 |
Kid's Slipper Size Chart
| UK | 9-10 | 11-12 | 13-1L | 2L-3L |
| S-XL | S | M | L | XL |
All Toddler's shoes sold by Number One Shoes are US sizes.
Toddler's Shoe Size Chart
| US | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| UK | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| EU | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| US | UK | EU |
| 2 | 1 | 17 |
| 3 | 2 | 18 |
| 4 | 3 | 19 |
| 5 | 4 | 20 |
| 6 | 5 | 21 |
| 7 | 6 | 22 |
| 8 | 7 | 23 |
| 9 | 8 | 24 |
| 10 | 9 | 25 |
Toddler's Slipper Size Chart
| UK | 9-10 | 11-12 | 13-1L | 2L-3L |
| S-XL | S | M | L | XL |