If you don't know what size you are, then you'll need a tape measure. Measure from under arm to under arm across your chest, then multiply by two. That's your chest measurement. Now check the size chart below.
T-shirts
| S |
Small
| Chest size 34 - 36 Inches |
| M |
Medium
| Chest size 38 - 40 Inches |
| L |
Large
| Chest size 42 - 44 Inches |
| XL |
Extra Large
| Chest size 46 - 48 Inches |
| 2XL |
Double Extra Large
| Chest size 50 - 52 Inches |
| 3XL |
Triple Extra Large
| Chest size 54 - 56 Inches |
| GFS |
Girl's Slim Fit Small (8)
| Chest size 30 Inches |
| GFM |
Girl's Slim Fit Medium (10-12)
| Chest size 31 Inches |
| GFL |
Girl's Slim Fit Large (14)
| Chest size 34 Inches |
| GFXL |
Girl's Slim Fit XL (16)
| Chest size 35 Inches |
| MF |
Men's Fitted
| Chest size 35 - 37 Inches |
| 3-4 |
Childs 3-4 years
| Chest size 22 - 24 Inches |
| 5-6 |
Childs 5-6 years
| Chest size 26 - 28 Inches |
| 7-8 |
Childs 7-8 years
| Chest size 30 Inches |
| 9-11 |
Childs 9-11 years
| Chest size 32 - 34 Inches |
| 12-13 |
Childs 12-13 years
| Chest size 34 - 36 Inches |
Vintage t-shirts
| M |
Medium
| Chest size 38 - 40 Inches |
| L |
Large
| Chest size 40 - 42 Inches |
| XL |
Extra Large
| Chest size 42 - 44 Inches |
| 2XL |
Double Extra Large
| Chest size 44 - 46 Inches |
| GF |
Girl's Slim Fit
| Chest size 34 - 36 Inches |
* All sizes are approximate.