| Gender | American size on label | NICKIS size in years | NICKIS size in CM |
| Girls | 2T | 2 | 88-93 |
| Girls | 3T | 3-4 | 90-100 |
| Girls |
4T | 4-5 | 102-108 |
| Girls |
5 | 5-6 | 109-116 |
| Girls |
6 | 6-7 | 117-123 |
| Girls |
6X | 7-8 | 124-128 |
| Girls |
S (7) | 8-9 | 130-134 |
| Girls |
M (8-10) | 9 | 136-142 |
| Girls |
L (12-14) | 11-12 | 144-154 |
| Girls |
XL (16) | 13 | 155-159 |
| Boys |
2T | 2 | 88-93 |
| Boys |
3T | 3-4 | 94-100 |
| Boys |
4T | 4-5 | 102-108 |
| Boys |
5 | 5-6 | 109-116 |
| Boys |
6 | 6-7 | 117-123 |
| Boys |
7 | 7-8 | 124-134 |
| Boys |
S (8) | 9 | 136-138 |
| Boys |
M (10-12) | 10-11 | 140-149 |
| Boys |
L (14-16) | 12-13 | 150-161 |
| Boys |
XL (18-20) | 14-16 | 163-174 |