The Shoulders Never Lie
Start with the shoulders, as they are the foundation of the entire garment. The seam where the sleeve attaches to the body of the jacket should end exactly at the edge of your shoulder bone. If the seam droops down your arm, the jacket is too big, creating
a slumped, oversized look. If the seam is creeping up toward your neck, it's too small, causing pulling and restricting movement. This is your most critical tell. Shoulder alterations are among the most difficult, expensive, and risky for a tailor to perform. They require deconstructing and rebuilding a core part of the jacket. If the shoulders don't fit, you almost always need a different size.
Buttoning Up the Chest and Waist
Fasten the top button of a two-button jacket or the middle button of a three-button jacket and stand naturally. Do you see a prominent 'X' shape forming from the strain? That means the jacket is too tight across your chest or waist. Conversely, if there's excessive, baggy fabric when buttoned, it's too loose. A good rule of thumb is that you should be able to slide a flat hand comfortably between your chest and the buttoned jacket. The good news is that this area is highly fixable. A tailor can easily take in the side or back seams to create a more defined, tapered silhouette, which is one of the most impactful alterations you can make. Letting a jacket out is possible, but only if there's enough extra fabric in the seams, which isn't always the case with off-the-rack garments.
Getting the Sleeve Length Right
Sleeve length is one of the most noticeable fit points and, thankfully, one of the easiest to correct. With your arms hanging relaxed at your sides, the jacket sleeve should end at about your wrist bone, allowing a quarter to a half-inch of your shirt cuff to be visible. If the sleeves are hiding your hands or showing too much shirt, it's a clear sign an adjustment is needed. Shortening or lengthening sleeves is a routine job for any competent tailor. The cost can increase if the jacket has functional buttonholes ('surgeon's cuffs'), as the alteration may need to be done from the shoulder to preserve the button placement, which is more complex. But in most cases, it's a straightforward and worthwhile fix.
The Non-Negotiable Jacket Length
The overall length of the jacket sets its proportion and balance. A classic rule is that the bottom of the jacket should cover the seat of your trousers. Another common guide is that with your arms at your sides, the hem should hit around your thumb's knuckle. A jacket that's too short can unbalance your silhouette, while one that's too long can make your legs appear shorter. Like the shoulders, the jacket's length is very difficult to alter significantly without ruining its proportions—the pocket and button placement will be thrown off. While a tailor might be able to shorten it by a very small amount, you can't add length. If the length is wrong, it's a fundamental sizing issue.
Checking the Collar and Back
Look at the back of your neck in a mirror. The jacket collar should rest smoothly against your shirt collar. If you see a space or gap between them, it's known as a 'collar gap'. This often indicates the jacket's balance or shoulder slope doesn't match your posture. While a skilled tailor can sometimes improve a minor gap, it can be a tricky and complex alteration. Also, check for horizontal wrinkles across your upper back, which suggest the jacket is too tight, or vertical folds of excess fabric, indicating it's too loose. Minor adjustments to the back and side seams can often resolve bagginess, but significant pulling or gaping often points back to a fundamental sizing problem that began with the shoulders.
