How a blazer should sit, from shoulder to hem.

Find the bone where your shoulder turns into your arm, then look at the seam. If that seam misses the bone, collar and sleeve become a negotiation you will lose. Several points on a blazer can be moved by a tailor. The shoulder is the decision you make before you pay.

A wrap coat is the wrong template. The camel coat in the photograph is cut with ease so it can close over a turtleneck and still belt. That ease belongs to an outer layer. A blazer is an indoor jacket. Its shoulder should sit closer to the body than a coat's, and it should not borrow a coat's width just because both look tailored.

The shoulder is the decision

Put the blazer on over the layer you will actually wear, a shirt or a thin knit, not a heavy sweater and not a bare camisole if you never dress that way. Let your arms hang. The seam should end at the shoulder point, where a finger feels the bone drop off.

If the seam rides past that point onto the upper arm, the jacket is large in the shoulder. You will see a small shelf of cloth just beyond the bone. If the seam stops short and the cloth pulls toward the neck, the jacket is small. The sleeve head creases, and the collar will not sit no matter how you tug it.

A field jacket can park its shoulder seam down the arm on purpose. That pattern has room for a sweatshirt and no plan to look sharp at the neck. Do not grade a blazer against that ease. If you need the blazer over a thick knit, either buy it for the knit and accept a softer line, or wear the coat instead.

Raise both arms, then drop them. The blazer should settle without a shrug. If you tug it straight after every gesture, the shoulder or the armhole is wrong. A lined shoulder is usually a rebuild, which is rarely worth it. Across the upper back, pinch a small fold, enough to move. An X of pull when you reach forward is a tight blade, and an open button does not fix it.

Collar and lapel

Button the jacket. The collar should touch the back of the neck. A gap that admits one finger is a warning. A gap the width of two fingers means the balance is off: the shoulder is wide, the back is long, or the jacket was cut for a posture you do not have. You want cloth against the shirt, with no tunnel of light at the nape.

Lapels should lie flat. A buckle at the outer edge is often a tight chest or a twisted front. Pressing calms a wrinkle for a day. It does not rebuild a lapel that will not lie down. Notch, peak, and shawl are shapes, not ranks. A notch is the usual partner for trousers and a desk day. A shawl is softer and closer to evening. Choose by the clothes you wear, not by a ladder of formality you do not use.

The gorge, where collar meets lapel, should match on both sides. A twist is a construction fault. A lapel that already ripples under the shop lights will not settle later.

Sleeves and the wrist

With the arm slightly bent, the way it is when you hold a cup, the sleeve should end at the wrist bone, the outer knob, not the start of the hand. If the sleeve covers the bone and touches the hand, it is long. If the bone is bare and no shirt cuff can show, it is short.

Over a dress shirt, show about a quarter inch to a half inch of cuff. That sliver means the sleeve was cut for a layer. More than half an inch of cuff starts to look like the shirt is long or the jacket is short. No cuff at all, on a shirt you meant to show, looks unfinished. Over a knit with no cuff, judge the sleeve by the wrist bone alone.

Check both arms. One shoulder is often lower, so one sleeve can be right and the other long. That is a tailor's job, not a new size. If the sleeve binds at the elbow, the seam will fail before the cloth looks old.

Ask whether the sleeve buttons open a real vent. A working vent shortens more cleanly. A closed vent can still be shortened, though the buttons may crowd the new hem. Neither issue outweighs a bad shoulder.

Where the button and the hem go

The button you fasten should sit at the smallest part of the waist, or just below it, not on the bust and not on the hip. On a single-breasted jacket, close the waist button. If a lower button pulls the hem into a smile, leave it open. Two buttons: the upper is usually the waist. Three: the middle is usually the working point. If the only calm button sits far from your waist, the stance is wrong for your torso, and another size in the same cut will likely repeat it.

From that button to the side seam, the cloth should be close but not tight. Lines radiating from the button mean the waist is small. A cone of empty cloth under the bust means there is no shape, and the jacket will look borrowed. Sit down. The button should stay closed, and the lapels should not climb. A jacket that only works while you stand in the fitting room does not work.

Hem length follows the layer underneath. Over trousers, cover the waistband and finish near the top of the thigh. A waist-length crop works with a high rise and looks chopped above a low rise, where a band of shirt shows. Over a dress, stop above the widest part of the hip or continue past it. Try your own clothes, not a matching skirt from the shop.

The blouse is what the blazer has to clear. If your cuffs are already long, measure the sleeve over them.

Point	What you should see	Usually alterable
Shoulder seam	Ends at the bone, with no shelf on the arm	Rarely, without a rebuild
Collar	Touches the neck when buttoned	Only when the cause is minor
Sleeve	Ends at the wrist bone, with a sliver of shirt cuff	Often, if the sleeve is long or has allowance
Waist button	Sits at the waist without horizontal pull	Side seams, by a small amount
Hem	Covers a trouser band, or clears a dress curve	Often shortened; lengthening needs spare cloth

Alterations that are worth asking about

Take the jacket to a tailor with the shoes and the bottom you will wear. Ask whether the sleeves can be shortened and whether the buttons open. Ask if there is cloth to lengthen them. Ask whether the side seams can come in, and by how much, without dragging the pockets. Ask if a small collar gap can be eased, or if the shoulder is the real cause.

Often worth doing: a shorter sleeve, a modest waist taken in or let out where allowance exists, and a hem that no longer swamps the skirt. Usually not worth doing: moving a shoulder seam that already sits down the arm, lengthening a sleeve with no cloth, or sliding a button to hide a chest pull. The pull remains. A tailor who will not touch the shoulder has given you the useful answer. Keep looking.

Read the live page before any seam is opened. Altered jackets are often not returnable. The current page, not your memory, is the rule.

• The shoulder seam meets the bone, with no shelf and no pull toward the neck.
• The collar touches the neck when the waist button is closed.
• The lapels lie flat and the two sides match.
• The sleeves end at the wrist bone, with a short show of cuff over a shirt.
• The working button sits at the waist and stays calm when you sit.
• The hem covers a trouser band or clears the widest part of a dress.
• You have asked which of those points a tailor can move.

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