Grab a shirt that fits you great, lay it down on a flat surface and measure its length and width.
Then use those measurements to find your size.
| Width (cm) | Length (cm) | |
| Small | 45.7 | 68.8 |
| Medium | 50.8 | 72.3 |
| Large | 55.8 | 74.3 |
| X-Large | 60.9 | 75.0 |
| XX-Large | 66.0 | 80.0 |