What does 40R actually mean?

Suit sizes look precise and aren't. Knowing what the label promises makes it much clearer why an off-the-rack suit fits some people beautifully and others not at all.

The number

The number is your chest measurement in inches — 40 means a 40-inch chest. The finished jacket is not 40 inches round; the maker adds ease, usually four to six inches, so you can move and breathe. How much ease is a house decision, which is why a 40 from one brand is roomier than a 40 from another.

The letter

The letter is length, and it is really a proxy for your height.

• S (short) — roughly 5'4" to 5'7"
• R (regular) — roughly 5'8" to 6'0"
• L (long) — roughly 6'1" to 6'3"

It changes the jacket length, the sleeve length and the position of the buttons and pockets all at once, in a fixed relationship.

What is bundled in that you don't choose

This is the important part. Buying a 40R commits you to a shoulder width, a sleeve length, a jacket length, a waist and an armhole height that the pattern-maker decided go with a 40-inch chest on a 5'10" man. If any of those don't match you, you either alter them, live with them, or size up or down and compromise somewhere else.

A suit size is one measurement doing the work of eight. It is a good guess, not a fit.

Drop

The other hidden assumption is "drop": the difference between the chest and the trouser waist, usually six inches. A 40 chest comes with 34 trousers. If your waist is 38, off-the-rack suits will never come as a set that fits you, which is why separates and made-to-measure exist.

Why we still ask for it

We ask for your usual jacket size on the measuring form, and it is optional. We don't cut from it — we cut from your measurements. It is a sanity check: if you tell us 40R and then measure a 46-inch chest, one of those is wrong, and it is better that we ask you now than that we cut a suit and find out later.