You try a blazer on over a thin T-shirt, check the mirror, nod in satisfaction and take it home. The following week you wear it over a crew-neck sweater, and the button refuses to fasten. It happens all the time, because choosing a men's blazer size is different from choosing a suit jacket: a blazer is a separate piece, and has to live with many different layers underneath.
Quick answer
Choose a blazer size by the shoulders first: the shoulder seam must sit exactly on the shoulder bone. Then check the chest with the button fastened (no X-shaped creases), sleeves that reach the wrist bone, and a hem that covers most of the seat. If you often wear it over a thin sweater, try the blazer on with that very layer.
How does a blazer differ from a suit jacket when choosing a size?
A suit jacket is part of a matching set, usually with firm structure, and is worn with a shirt. A blazer is freer:
- It can be worn over a shirt, T-shirt, polo or thin sweater.
- The cloth and interlining are usually softer, and some are almost unstructured.
- It must let the wearer move more comfortably on relaxed occasions.
So a blazer needs slightly more room to “breathe” than a suit jacket at the chest and arms, but the shoulders still have to fit exactly.
How to choose a men's blazer size: five checks when trying on
1. Shoulders
The shoulder seam should land right at the tip of the shoulder. If it drops onto the upper arm, the jacket is too wide in the shoulders. If it rides up toward the neck or presses tightly, it is too tight. This is almost impossible to alter, so it is the first thing to check.
2. Chest with the button fastened
Fasten the button and stand straight. The button should lie still, without pulling into an X-shaped crease around it. If a flat, open hand slips in between chest and jacket, that is a reasonable level of comfort. If a whole fist goes in easily, the jacket is loose.
3. Jacket length
A simple check: stand straight and let your arms hang naturally. The hem should cover most of the seat, or reach about the second joint of your thumb when your hand is closed. A blazer is usually slightly shorter than a suit jacket. Tall men can choose a longer one; shorter men a shorter one so that the legs look longer.
4. Sleeves
The sleeves reach the wrist bone. If you wear a shirt underneath, let about one centimetre of shirt cuff show. Blazer sleeves that are slightly short or long can be altered, as long as the shoulders and upper arms fit.
5. Collar
The collar must hug the nape of the neck, without gapping when you bend or move. A gapping collar is a sign the jacket does not yet fit the back or shoulders.
Reference men's blazer size chart
The chart below is a reference only for ready-to-wear, since every brand has its own cut. With made-to-measure, you don't depend on this size chart.
| Size | Height (cm) | Weight (kg) | Chest (cm) |
|---|---|---|---|
| XS | 155 – 165 | 48 – 56 | 82 – 88 |
| S | 160 – 168 | 55 – 62 | 86 – 91 |
| M | 165 – 172 | 60 – 68 | 90 – 95 |
| L | 170 – 177 | 66 – 74 | 95 – 100 |
| XL | 173 – 180 | 72 – 80 | 100 – 106 |
| XXL | 175 – 185 | 78 – 90 | 106 – 112 |
If you fall between two sizes, choose by the shoulders. Chest and waist can be taken in or let out; the shoulders cannot.
Small (XS) and large (XXL) blazers: specific notes
- XS or small-size blazers: slightly built men often find the shoulders fit but the sleeves are too long. Sleeves can be shortened. Avoid picking a larger size to be “roomy”, because the shoulders will drop and it will look as if you are wearing borrowed clothes.
- XXL blazers: men with a broad build usually have trouble with the stomach girth and the collar. Favour a single-breasted style, cloth with good drape and a length sufficient to cover the stomach. If ready-to-wear runs short of sizes, made-to-measure is the least troublesome solution.
Blazer over a shirt or over a thin sweater?
This affects size more than you might think:
| Layer underneath | Suggestion when trying on |
|---|---|
| Shirt | Choose a size that fits the shoulders, lightly fitted at the chest |
| T-shirt, polo | Can be slightly closer-fitting, since the layer underneath is thin |
| Thin sweater | Try it on with that exact sweater; body and sleeves need more room |
| Thick sweater | Almost needs its own cut; ready-to-wear struggles to accommodate it |
If you usually wear a blazer over a sweater, bring the sweater when you try it on. A small tip, but it saves a great many returns and exchanges.
When you can't try it on: buying online or for someone else
You don't always have the chance to try a jacket on. In that case, don't trust the S, M, L on the label; use real measurements:
- Take the blazer or suit jacket that currently fits you best and lay it flat on a table.
- Take four measurements: shoulder width (from one shoulder seam to the other), chest width (measured under the armpit, then doubled), jacket length (from the base of the collar to the hem) and sleeve length (from the shoulder seam to the cuff opening).
- Compare them with the measurement chart of the item you want to buy, prioritising a match in shoulder width first, then sleeve length.
If you often have to buy this way and it still comes out off, it may be time to use your own measurements. With the online made-to-measure service, Mon Amie guides you through measuring by video or uses your saved measurements, so you no longer have to guess your size.
Common mistakes
- Choosing a size by the stomach and forgetting the shoulders. Wrong shoulders means a wrong jacket.
- Trying a blazer on without fastening the button. A jacket only shows its faults at the chest and waist once fastened.
- Choosing a loose size for comfort. A blazer that is wide in the shoulders looks untidy, not comfortable.
- Mistaking a blazer for a sports jacket. A blazer needs to keep its lines; it isn't meant to be as loose as a jacket.
- Trying it on only standing. Sit down, raise your arms and bend slightly to check.
A tip from Mon Amie's master tailors
The surest way to choose a men's blazer size is still to try it on with the very layer you will wear underneath. When you do, make one movement: bring both arms forward as though hugging something large. If the back strains as if about to tear, the jacket is too tight. If the chest and shoulders follow along and you are still comfortable, it fits. Another tip is to measure against the jacket that suits you best, then compare it with the blazer you plan to buy: if the two differ by more than two centimetres at the shoulders, change the size.
For more related guides, you can read how to choose a men's blazer and the chart for converting men's suit sizes to European standards.
Frequently asked questions
What is the standard length for a men's blazer?
The hem should cover most of the seat, reaching about the second joint of the thumb when your arms hang. A blazer is usually slightly shorter than a suit jacket, and shorter men should choose a shorter one so that their legs look longer.
Can a small-size men's blazer be altered?
The sleeves, body or hem can be altered if the shoulders fit. If the shoulders are too wide, it is very hard to alter and keep the shape, so get the shoulder size right first.
Who suits an XXL blazer, and what should you watch for?
It suits men with a large frame, tall men or those with broad shoulders. Choose a single-breasted style, cloth with good drape, and make sure the fastened button isn't strained at the stomach. If you can't find a size that fits, consider made-to-measure.
Is an XS blazer suitable for a tall, slim man?
If the shoulders fit but you are tall, an XS blazer is usually short in the body and the sleeves. You should try size S or go made-to-measure to get the right length.
An invitation
If you are still torn between sizes or can't find a jacket that fits at the shoulders, book a measuring appointment and Mon Amie, a made-to-measure tailor in Ho Chi Minh City, will take your own measurements for your blazer. You can also see more styles on the products page or learn about the process in the bespoke service.