What Size Jacket Should I Buy? Men's Jacket Sizing Guide (2026)
Two jackets on this site both labelled L measure 42.5 and 48.0 inches across the chest. Here is how to read the number instead of the letter.
Last updated: September 2026
Buy the jacket whose published chest measurement is 3 to 5 inches larger than your own chest. Across the 79 active jackets at Adam & Westcott a size L spans 42.5 to 48.0 inches, so the letter cannot tell you the fit. The chart on the product can.
What size jacket should I buy?
Measure your chest, then pick the jacket whose own chest measurement is 3 to 5 inches larger. A 38 inch chest fits the size L Classic Casual Jacket at 42.5 inches.
Jacket charts list the garment, not the body. That 3 to 5 inch gap is the room you need to move and to layer. Under 3 inches the jacket pulls when you close it. Over 5 inches it hangs off the shoulder.
Why does a size L differ between two jackets?
Because the cut differs. At Adam & Westcott the size L 
Classic Casual Jacket measures 42.5 inches in the chest, and the size L 
Stand Collar Bomber Jacket measures 48.0 inches, a gap of 5.5 inches in the same letter.
One is cut close for wear over a shirt, the other relaxed for wear over a sweater. Both are honest sizes, which is why the number matters more than the letter.
| Size |
 Classic Casual Jacketchest / length, inches |
 Stand Collar Bomber Jacketchest / length, inches |
Chest gap |
|---|---|---|---|
| S | 39.4 / 25.6 | 44.9 / 26.0 | 5.5 in |
| M | 40.9 / 26.0 | 46.5 / 26.8 | 5.6 in |
| L | 42.5 / 26.4 | 48.0 / 27.6 | 5.5 in |
| XL | 44.1 / 26.8 | 49.6 / 28.3 | 5.5 in |
| 2XL | not stocked | 51.2 / 29.1 | n/a |
| 3XL | not stocked | 52.8 / 29.5 | n/a |
As published on each product. Classic Casual Jacket, S to XL, $59.99. Stand Collar Bomber Jacket, S to 3XL, $70.98.
How do I measure my chest for a jacket?
Run a tape around the fullest part of your chest, under the arms and over a t-shirt, level across the back. Your jacket chest should read 3 to 5 inches higher than that.
Check length too. The Classic Casual Jacket runs 25.6 inches long at S to 26.8 at XL. The Stand Collar Bomber Jacket runs 26.0 inches at S to 29.5 at 3XL.
What size jacket should I buy to wear over a sweater?
Size up one letter. Each step adds about 1.6 inches of chest on both Adam & Westcott jackets that publish a chart, which is roughly what a mid weight sweater takes up.
That step holds on both: 1.6 inches from L to XL on each. Before sizing up, check the size exists. 2XL is stocked on 96 percent of the range, 3XL on only 44 percent.
Which jacket sizes does Adam & Westcott actually stock?
M, L and XL appear on all 79 active jackets. 2XL is on 96 percent, S on 91 percent, XS on 52 percent, 3XL on 44 percent and 4XL on just 13 percent.
- M, L, XL: 79 of 79 jackets, 100 percent of the range.
- 2XL: 76 of 79, 96 percent.
- S: 72 of 79, 91 percent. Seven jackets start at M with no S at all.
- XS: 41 of 79, 52 percent. 38 jackets skip it.
- 3XL and above: 35 jackets reach 3XL, 10 reach 4XL, 6 reach 5XL and 4 reach 6XL.
Runs span 4 to 10 sizes, median 6. The widest is the 
Suede Bomber Jacket at 10 sizes, XS through 6XL. The narrowest is the 
Alpine Explorer Windbreaker at 4, S through XL.
Widest size run: Suede Bomber Jacket
Ten sizes, XS through 6XL, the only jacket covering the full spread. New this month, cut for layering. $79.98.
Frequently asked questions
Should I size up or down in a jacket if I am between sizes?
Size up. A jacket an inch too big still closes and layers, one an inch too small pulls across the back. Each size step adds about 1.6 inches of chest.
Is jacket chest measurement the same as my body chest?
No. The chart lists the garment laid flat and doubled, so it reads 3 to 5 inches larger than the body it fits. A 42.5 inch jacket chest suits roughly a 38 inch body chest.
What size jacket is a 40 inch chest?
A 40 inch chest takes a jacket measuring 43 to 45 inches. That is an XL in the Classic Casual Jacket at 44.1 inches, or an S in the Stand Collar Bomber Jacket at 44.9 inches.
Do Adam & Westcott jackets run big or small?
Neither consistently. Cut decides it. A size L spans 42.5 to 48.0 inches across the range, so read the chart on the jacket you want.
Which jacket should I buy for a 3XL fit?
Thirty five of the 79 active jackets reach 3XL, including the Stand Collar Bomber Jacket at 52.8 inches in the chest. Ten go on to 4XL and four reach 6XL.
More sizing from Adam & Westcott: the Adam & Westcott size chart covers what S to 3XL measures across the shirt range, and what size vest to wear over a sweater works through the same layering question for vests.