Jacket Size Calculator

Background.

A jacket size calculator converts a chest girth and your height into the size on a tailored jacket's label. Menswear is unusually straightforward here, because the number is not an index — it is a measurement. ASTM D6240/D6240M, the standard tables of body measurements for adult males, is titled for a chest size range of 34 to 52 in Short, Regular and Tall, which tells you both facts a jacket buyer needs: the number is your chest in inches, and the letter after it is a length class driven by your height. A 40R is a jacket cut for a 40-inch chest on a body of average height.

The continental series works the same way in different units. The European number is half your chest girth in centimetres, which is why it runs 46, 48, 50, 52 in steps of two — EN 13402-3 sets girth intervals of four centimetres for body-measurement labelling, and four centimetres of chest is two continental numbers. A 100-centimetre chest is a continental 50.

Here is where this page deliberately differs from every conversion chart you will find, and it is worth understanding before the result surprises you. Those charts say continental equals US plus ten: 40 becomes 50, 42 becomes 52. That is exact near a 100-centimetre chest and it drifts everywhere else, because the two series are graded on different intervals. The US number advances two for every two inches of chest — 5.08 centimetres. The continental number advances two for every four centimetres. Two scales with different step sizes cannot be a fixed offset apart at more than one point. So this calculator derives each series from your own measurement rather than from the other series, and when the two disagree with the plus-ten chart it tells you both numbers and says why. At a chest of 102 centimetres, for instance, you are a US 40 and a continental 52, where the chart would have said 50. Try both.

The length class is the part most people get wrong, and it matters more than the number. A jacket's chest can be let out or taken in by a tailor; its length, its shoulder and its sleeve pitch essentially cannot. The classes here are Short below five foot eight, Regular from five foot eight to just under six foot, Long from six foot to just under six foot four, and Extra Long above that. ASTM's own tables use three classes — Short, Regular and Tall — and retail adds a fourth at the top; the page prints the height range with the class so you can check it against a specific brand's definition rather than trusting the word.

The trouser waist figure comes from the conventional six-inch drop: a suit sold as a 40 usually comes with 34-inch trousers. Athletic cuts drop seven or eight inches and portly cuts four or fewer, so the number here tells you what to expect rather than what you will get, and the page says so beside it.

What this page cannot do is worth stating plainly. It does not know your shoulder width, your sleeve length, your posture or your back length, and those are what a jacket lives or dies on — a correctly numbered jacket with the shoulder seam an inch off the end of your shoulder is the wrong jacket. It does not cover women's tailoring, which is graded on bust, waist and hip rather than chest alone; the dress size calculator is the right starting point there. And nothing enforces any of these numbers: PS 45-71, the only US government standard for sizing menswear, was withdrawn, and ASTM's tables are voluntary. Use the result to pick what to try on, and judge the jacket on the shoulder.

What is jacket size calculator?

A jacket size is a chest measurement plus a length class. On the US and UK scale the number is the chest girth in inches — a 42 is cut for a 42-inch chest — and the letter that follows it, S, R, L or XL, says which of the length gradings it belongs to. On the continental scale the number is half the chest girth in centimetres, so a 104-centimetre chest is a 52. Italy uses the same numbers as Germany and the rest of the continent for tailoring.

Both conventions are documented in the standards that tabulate the underlying body measurements. ASTM D6240/D6240M-24a covers adult male body measurements over a chest size range of 34 to 52 in Short, Regular and Tall gradings; ISO 8559-1:2017 defines how chest girth and stature are located and measured; EN 13402-3:2017 sets the four-centimetre girth and eight-centimetre height intervals that European labelling is built on. What none of them do is compel a manufacturer, and the US government standard for menswear sizing, PS 45-71, has been withdrawn.

The practical upshot is better than it is for women's sizing — a chest number in inches is a real, checkable dimension, and men's labels show little of the size inflation documented in women's apparel — but it is still a starting point. The jacket that fits is the one whose shoulder seam ends where your shoulder does.

How to use this calculator.

1. 01Pick your unit and use it for both measurements.
2. 02Measure your chest: tape round the fullest part, high under the arms, level all the way round. Arms down, breathing normally, wearing a shirt rather than a jumper. Do not pull tight — the jacket's own ease is already built in.
3. 03Measure your height standing without shoes. This sets the length class, not the number.
4. 04Choose the labelling system for the market you are buying from — continental numbers, US/UK inch numbers with a length letter, or plain letters.
5. 05Read the size, then read the length class and check its printed height range against the retailer's own definition of Short, Regular or Long.
6. 06Note the trouser waist from the six-inch drop, but verify it against the actual trousers — athletic and portly cuts use different drops.
7. 07If the page warns that the continental and US numbers disagree with the plus-ten chart, you are on a boundary between the two gradings. Try both numbers.
8. 08Try the jacket on and check the shoulder first: the seam should end where your shoulder does. A tailor can adjust the chest and the sleeve length; nobody can move the shoulder.

The formula.

The chest girth is converted to both inches and centimetres up front, because each series is defined in its own unit. The US/UK number is the chest in inches rounded to the nearest even inch, half-up, because tailored jackets are graded in two-inch steps. The continental number is half the chest in centimetres rounded to the nearest even number, which is the same thing as rounding the chest to the nearest four centimetres — EN 13402-3's own girth interval — and dividing by two.

Deriving each series from the measurement rather than from the other series is a deliberate choice with a visible consequence. The US number moves two units per 5.08 centimetres of chest; the continental number moves two units per four centimetres. They are not the same grading, so no constant offset converts between them at every chest. Where the two results differ from the familiar "continental = US + 10" chart, the page prints both numbers and explains the divergence rather than quietly picking one. This happens at chests near the middle of a continental step: at 102 centimetres the US number is 40 and the continental number is 52, where the chart would have said 50.

The two banded outputs read the unrounded inch values, never the rounded size number. A 41.9-inch chest rounds to size 42 but bands as M, because the L band begins at 42.0 inches — classifying the rounded number would have printed "42 / L" for a body that is genuinely below the L threshold. A 67.9-inch height would round to 68 but bands as Short, because Regular begins at 68.0 inches. Both cases are tested at, below and above every edge: length classes at 68, 72 and 76 inches, letter sizes at 34, 38, 42, 46 and 50 inches.

The trouser waist is the jacket number minus six, the conventional drop, and it is reported as an expectation rather than a fact because athletic and portly cuts use different drops. A warning appears when the resulting chest size falls outside the 34-to-52 range ASTM D6240 tabulates and most ready-to-wear brands stock.

Worked through with the page's own example: a 40-inch chest gives 2 × round(40 ÷ 2) = 40 on the US/UK scale. In centimetres that chest is 101.6, so the continental number is 2 × round(101.6 ÷ 4) = 50 — which does agree with the plus-ten chart at this chest, so no divergence warning appears. A height of 70 inches falls in the Regular band (68 to just under 72), giving the code R, so the size is 40R. The 40-inch chest bands as M on the letter scale, and the six-inch drop gives a 34-inch trouser waist.

A worked example.

Frequently asked questions.

References& sources.

1. [1]ASTM International, ASTM D6240/D6240M-24a — Standard Tables of Body Measurements for Adult Male, Chest Size Range 34–52 Short, Regular, and Tall. The authority for the men's size number being a chest measurement in inches and for the Short/Regular/Tall length gradings. Sold by ASTM; designation, title and scope consulted, not the measurement tables.
2. [2]International Organization for Standardization, ISO 8559-1:2017 — Size designation of clothes, Part 1: Anthropometric definitions for body measurement. Defines chest girth and stature, the two dimensions this page takes. Sold by ISO; catalogue entry consulted.
3. [3]European Committee for Standardization, EN 13402-3:2017 — Size designation of clothes, Part 3: Size labelling based on body measurements and intervals. Sets girth intervals of 4 cm (±2 cm) and height intervals of 8 cm (±4 cm); the 4 cm chest interval is why the continental number is half the chest in centimetres. Sold by CEN national members; abstract and scope consulted.
4. [4]National Institute of Standards and Technology, "Withdrawn DOC Product Standards (PS)" — lists PS 45-71, Body Measurements for the Sizing of Apparel for Young Men (Students), among the withdrawn US Department of Commerce standards. No current US government menswear sizing standard exists.
5. [5]Franz W-JI. "Economics of vanity sizing." Journal of Economic Behavior & Organization 2017;134:336–355. doi:10.1016/j.jebo.2017.01.004. Across the size charts of 54 American apparel retailers, found women's sizes inflated but "little, if any, vanity sizing in men's or children's apparel" — the evidence behind treating a men's chest number as a reasonably honest measurement.