Mack Weldon vs Under Armour: which size fits the same?
In tees, a Mack Weldon L is closest to an Under Armour M (1″ roomier). In polos, a Mack Weldon L is closest to an Under Armour L (1″ roomier).
Tees
Under Armour tees measure about 4″ more around than Mack Weldon at the same size. A Mack Weldon L is closest to an Under Armour M (1″ roomier).
| Mack Weldon | Chest · length | Closest Under Armour | Chest · length | Under Armour is |
|---|---|---|---|---|
| Mack Weldon S | 38″ · 28″ | Under Armour S | 40″ · 28¾″ | 2″ roomier |
| Mack Weldon M | 40″ · 29″ | Under Armour S | 40″ · 28¾″ | the same around |
| Mack Weldon L | 42″ · 29¾″ | Under Armour M | 43″ · 29¼″ | 1″ roomier |
| Mack Weldon XL | 44″ · 30½″ | Under Armour M | 43″ · 29¼″ | 1″ snugger |
| Mack Weldon XXL | 46″ · 31″ | Under Armour L | 46″ · 29¾″ | the same around |
From Mack Weldon: Mack Weldon SILVER Crew Neck T-Shirt, Mack Weldon Pima Crew Neck T-Shirt, Mack Weldon Pima Short Sleeve Henley. From Under Armour: Under Armour Team Tech Tee (1376842), Under Armour Athletic 2.0 Tee (1383264). Relaxed and oversized cuts are left out.
Polos
Under Armour polos measure about 1″ more around than Mack Weldon at the same size. A Mack Weldon L is closest to an Under Armour L (1″ roomier).
| Mack Weldon | Chest · length | Closest Under Armour | Chest · length | Under Armour is |
|---|---|---|---|---|
| Mack Weldon S | 41″ · 27½″ | Under Armour S | 40½″ · 29″ | ½″ snugger |
| Mack Weldon M | 43″ · 28½″ | Under Armour M | 43½″ · 29½″ | ½″ roomier |
| Mack Weldon L | 45½″ · 29¾″ | Under Armour L | 46½″ · 30″ | 1″ roomier |
| Mack Weldon XL | 48″ · 30½″ | Under Armour L | 46½″ · 30″ | 1½″ snugger |
| Mack Weldon XXL | 50″ · 31″ | Under Armour XL | 49½″ · 31″ | ½″ snugger |
From Mack Weldon: Mack Weldon Heavyweight Slub Polo, Mack Weldon SILVER Pique Polo. From Under Armour: Under Armour Tech Polo (1370399). Relaxed and oversized cuts are left out.
More: Mack Weldon sizing · Under Armour sizing
Get your exact size in any of these
Add three shirts you own that fit well. FitCard compares their real measurements with every shirt here and tells you the one size to buy, and why, in terms of your own shirts. Free, no tape measure.
Garment measurements: the shirt itself, chest all the way around and length from shoulder to hem, from each brand's own chart or wholesale spec sheet, checked November 2026. Shirts with half or more cotton are shown as they come out of a dryer (about 2% less around and 4% shorter). Brands change their cuts, so check the shop's chart before you buy.