Quick Answer: A blazer sleeve should end at the wrist bone, showing about half an inch of shirt cuff. That single measurement tells you whether the whole garment was drafted for your proportions, because sleeve length is graded from the same shoulder point as the armhole and chest. If the sleeve is right, the rest of the fit is usually close; if it is more than an inch off, it rarely is.

There are five things people check on a blazer and they check them in the wrong order.

Start with the sleeve. It is the fastest diagnostic in tailoring and it takes two seconds.

Why does the sleeve predict the rest of the fit?

Because it is measured from the same origin point as everything else that matters.

Sleeve length is graded from the shoulder point, which is also where the armhole and the chest width are calculated from. If a brand’s shoulder point matches your body, the sleeve will land correctly, and so will the armhole.

A sleeve that is far off means the shoulder point is off, which in turn means the armhole is sitting in the wrong place — the fit problem that cannot be altered affordably.

This is why the sleeve is a diagnostic rather than just a measurement. It is standing in for three other things you cannot easily check in a fitting room.

The exception: brands that deliberately cut long sleeves for a relaxed look. Those are identifiable because the shoulder seam is also dropped, and the two go together.

Where exactly should the sleeve end?

At the wrist bone — the knob on the outside of your wrist — with the arm hanging naturally.

Half an inch of shirt cuff should show below it. That is the traditional standard and it exists for a practical reason: the shirt cuff protects the jacket sleeve from wear, and the visible cuff creates a clean break between jacket and hand.

Check it with your arms hanging, not held out. Raising your arms pulls the sleeve up and gives you a false reading, which is why fitting-room sleeve checks are so often wrong.

A sleeve ending past the wrist bone shortens the visible arm and makes the whole blazer read as borrowed. A sleeve ending well above it reads as too small even when the body fits.

One inch either way is alterable. More than that and the sleeve head, buttons, and any lining detail start fighting the alteration, which is when it becomes expensive.

What are the other checks, in order?

Four more, and they take about thirty seconds total once the sleeve has passed.

Shoulder seam second. It should sit at the outer edge of your shoulder bone, unless the blazer is deliberately oversized. This is the alteration you should never plan to pay for.

Armhole third. Raise your arms to shoulder height. If the whole blazer lifts, the armhole is too low. A well-cut armhole sits high and lets the arm move independently of the body.

Button pull fourth. Fasten the top button and look for a horizontal fold or an X-shape below it. Any X means the blazer is too tight through the chest, and that is a different size rather than an alteration.

Length last. A blazer should cover the seat, roughly — though this is the most flexible of the five and it varies with the style. It is also the easiest to alter, which is why it belongs at the end of the list.

The order matters because the first three cannot be fixed cheaply and the last two can.

Myth vs Fact: Blazer Fit

Myth: you should buy a blazer that fits your chest and alter the rest. Fact: buy for the shoulder, then the chest. A shoulder that fits with a slightly loose chest is a twenty-minute alteration; the reverse is a rebuild.

Myth: sleeve buttons mean it is a better blazer. Fact: functioning sleeve buttons — surgeon’s cuffs — signal higher construction and also make sleeve alterations harder and more expensive. On a blazer you may need shortened, non-functioning buttons are the more practical feature.

Myth: a blazer should always be buttoned. Fact: the fit should be checked buttoned and the blazer can be worn either way. A blazer that only looks right open is too tight; one that only looks right closed usually has a shoulder or armhole problem.

Myth: shoulder pads are outdated. Fact: almost every well-cut blazer has some shoulder structure, and removing it collapses the line the garment was designed around. What changed is the size of the pad, not its existence.

Fact worth keeping: check the back. Most people check a blazer from the front only. Horizontal drag lines across the upper back mean the shoulders are too narrow, and a bubble under the collar means the neck is not sitting right — both are visible only from behind and both matter.

What is worth altering and what is not?

A short cost hierarchy, and it saves both money and disappointment.

Sleeve length: worth it, thirty to sixty dollars. The most common alteration and the one with the largest visual return.

Body taper at the waist: worth it, thirty to fifty dollars. Turns a boxy blazer into a shaped one and is straightforward on most constructions.

Hem length: worth it, moderate cost, though it changes the pocket-to-hem proportion so it has limits.

Shoulder narrowing: rarely worth it, one hundred and fifty dollars and up. Requires detaching and reattaching the sleeve on both sides. Only sensible on an expensive blazer you love.

Armhole raising: not available at sensible cost. This is a pattern-level issue.

The practical rule: budget about a third of the blazer’s price for alterations on anything off the rack, and choose the blazer knowing that the sleeve and waist are the two you will actually pay for.

FAQ: Blazer Fit Questions, Answered

What if I am between sizes?

Take the size that fits your shoulders, then have the body taken in. Chest and waist are alterable; shoulders effectively are not.

Should the sleeve length change if I do not wear shirts under it?

Slightly. Without a shirt cuff to show, ending exactly at the wrist bone looks right; the half-inch allowance exists to reveal the cuff. Over a knit, the same wrist-bone rule applies.

How do I check the armhole without looking odd in a shop?

Reach forward as if picking something off a table, then raise both arms to shoulder height. If the body of the blazer lifts or the fabric pulls hard across the back, the armhole is too low.

Is an oversized blazer measured differently?

Yes for the shoulder and no for the sleeve. An oversized blazer has a deliberately dropped shoulder seam, but the sleeve should still end at or very near the wrist bone — cuffed if necessary. That is what separates deliberate oversizing from a bad fit.

TL;DR: Check the wrist first. It answers most of the question.

• The sleeve should end at the wrist bone with half an inch of cuff showing.
• Sleeve length is graded from the shoulder point, so it predicts the armhole and chest.
• Then check, in order: shoulder seam, armhole lift, button pull, and length last.
• Buy for the shoulder. It is the one alteration never worth paying for.
• Sleeve and waist taper are the two alterations that earn their cost.
• Check the back. Drag lines and collar bubbles are invisible from the front.

Go look at the wrist on the blazer you own and feel lukewarm about. If it is more than an inch past the bone, that is what has been bothering you.