Shirt Size Calculator

A shirt size is a label for the body a shirt is cut to fit. Men's dress shirts are sized by neck and sleeve, so 15.5 / 34 means a 15.5 inch collar and a 34 inch sleeve. The international standard ISO 8559-2 names neck girth as the main size measure for men's shirts, bust girth for women's blouses and chest girth for men's knitwear such as T-shirts¹. This calculator follows the same split.

What Shirt Size Measures

It matches your body to a size on a published chart. It cannot see a brand's cut, the fabric's stretch or your shoulder width, so treat the result as a starting size. ASTM publishes US body measurement tables for men (chest sizes 34 to 52) and women (misses sizes 00 to 20), but they are paywalled² ³, so this tool uses named retailer charts.

The Formula

Collar (US and UK) = neck + 1/2 inch, rounded up to the next 1/2 inch

EU collar = neck in cm + 1.27 cm, rounded up to the next whole cm

Sleeve = center back of neck to wrist, rounded to the nearest inch

Casual letter size = the larger of your chest size and waist size on the chart

Women's US size = the chart size closest to your bust; UK and Australian size = US + 4; EU size = US + 32

The half inch allowance comes from a menswear retailer's measuring guide⁴. If you measure with one finger under the tape, nothing is added, because the finger supplies the room⁵.

How This Calculator Computes Your Result

Pick a shirt type and enter inches or centimeters (centimeters are divided by 2.54, with no early rounding).

• Men's dress shirt: neck, and how you measured it. Sleeve, chest and waist are optional. You get US, UK and EU collars, a sleeve size, a letter size and a regular or tall sleeve note from L.L.Bean's chart⁶, plus a slim versus classic fit check.

• Men's casual shirt: chest, and waist if you like. You get a US letter from L.L.Bean⁶, a UK letter from Next⁷, and your chest in whole cm, the way the European standard labels clothes⁸.

• Women's top: bust. You get a US size and letter from L.L.Bean⁹, UK, EU and Australian sizes from ASOS's conversion chart¹⁰, and the Next letter for comparison⁷.

What Your Result Means

Dress shirt collars come in half inch steps. Letters are L.L.Bean's⁶.

European collars come in whole cm. A 15.5 collar is 39.4 cm, so one French shirtmaker sells both 39 and 40 as 15.5⁵. The calculator rounds your own measurement up to the next cm.

Casual letters, in inches (US from L.L.Bean⁶, UK from Next⁷). A chest or waist in a gap between two US ranges gets the larger size.

Women's tops, by bust (L.L.Bean⁹, converted with ASOS¹⁰). Plus sizes such as 16W or 1X use a separate chart and are not covered⁹.

How to Measure Correctly

• Use a soft tape. Stand straight and breathe normally⁸.

• Neck: around the base of your neck where a collar sits, just below the Adam's apple⁴ ⁸. Let the tape rest on the skin ("tape snug"), or slip one finger under it ("one finger")⁵.

• Or measure a shirt that fits: lay it flat and measure from the center of the collar button to the far end of the buttonhole⁶.

• Sleeve: arm relaxed and slightly bent. Go from the center back of your neck, over the shoulder point, down the outside of the arm to the wrist⁶. European "arm length" starts at the shoulder point, so it is a different, shorter number⁸.

• Chest: around the fullest part, under the arms and across the shoulder blades, firm and level⁶ ⁸.

• Bust: around the fullest point, tape level⁹.

• Measure your neck twice and use the larger reading.

Slim Fit Versus Classic Fit

Fit names describe the room a shirt leaves around your body. The collar stays the same. On Charles Tyrwhitt's chart, a 15.5 collar made for a 40 inch chest and 34 inch waist leaves 5.5 inches of chest room in Classic, 4 in Slim and 1.5 in Extra Slim. At the waist it leaves 11, 7 and 4.5 inches¹¹. So most of the difference is at the waist. L.L.Bean describes it the same way: traditional is relaxed through the chest and waist, slim is cut slim through both⁶.

The fit check compares your chest and waist with those finished shirt sizes. It names the slimmest fit that leaves at least 1 inch at the chest and 4.5 inches at the waist, the least room Charles Tyrwhitt gives in any fit¹¹. With a 15.5 collar, a 44 inch chest and a 40 inch waist, Slim leaves 0 and 1 inch, so the answer is Classic (1.5 and 5 inches).

Why a Tight Collar Matters

In one study, 67% of 94 white-collar working men wore neckwear tighter than their neck, and in 22 men a tight collar and tie lowered a test of visual performance¹². In 40 men, three minutes in a tight necktie raised eye pressure by 2.6 mm Hg on average in healthy men and 1.0 mm Hg in men with glaucoma¹³. In an MRI study of 30 volunteers, blood flow to the brain fell after a necktie was tightened¹⁴. These are small studies of collar plus tie, but they back the usual check: with the collar buttoned, one or two fingers should fit inside⁴.

Why Sizes Differ Between Brands

ASTM's tables are only a baseline for designers², and each brand builds its own chart⁶ ⁷ ¹¹ ¹⁵.

Charles Tyrwhitt sells a 15 collar as Small, where L.L.Bean calls it Medium⁶ ¹¹. A US 8 top is a Small at L.L.Bean but a Medium at Next⁷ ⁹. Between collar sizes, take the larger one⁵. Between letter sizes, try both if you can and check the brand's own chart.