A denim jacket should fit its intended silhouette and underlayers while allowing ordinary movement. Close, regular and oversized cuts can all be appropriate. Decide the role before judging the amount of room.
Try the normal underlayer
Wear the tee, shirt or hoodie you expect to use. Close the jacket and check chest tension, shoulders and upper-back reach. Thick denim can feel firm at first, but that is different from a pattern that is too narrow.
Inspect cuffs and body length. A short jacket may be intentional, but it should work with your trouser rise and seated coverage. Sleeves should remain usable when bending your arms and handling everyday items.
Use measurements with the fit test
Compare chest width, shoulder construction and length with a reference jacket using the same method. Stretch denim, rigid denim and lined versions can provide different internal space at similar outer measurements.
If you need room for a hoodie, do not automatically size up without checking added sleeve and body length. A relaxed cut or a different pattern can provide layering room more cleanly.
Will it stretch enough if it is tight?
Do not rely on a dramatic change. Material and construction vary, and seams or lining can restrict movement. Buy a jacket that works now for the intended use. For teams, approve a fitted sample after any logo or patch is applied, because decoration can stiffen a panel.
Related reading
Agreeing jacket measurement methods and tolerances. For another useful reference, see Fitting outdoor team jackets across sizes.
