How to Measure a Shirt

The definition: “Lay flat, measure straight across 1" below the armholes, seam to seam.”

Where the tape goes. Find the two points where the sleeve seams meet the side seams — the pits. Come down one inch from each, then run the tape straight across, edge to edge, crossing the side seams at a right angle. Start at the left seam edge, stop at the right seam edge.

The common mistake. Measuring level with the armhole itself, where seam bulk and the folded sleeve distort the width. An inch below, the body lies flat and the number repeats. This is the single most published number in size charts and the heaviest input in ShirtMath’s fit scoring, so it is worth taking twice. Pit to pit measurement goes deeper.

The definition: “From the highest point of the shoulder seam straight down to the bottom hem.”

Where the tape goes. Anchor at the high point of shoulder, written HPS — the place the shoulder seam runs into the collar. Drop the tape dead straight to the bottom edge of the hem. It does not follow the curve of the chest, and it does not stop at the top of the hem band.

The common mistake. Starting at the collar’s top edge, which adds the collar height to every shirt you own and makes them all read long. If the hem is curved, measure at the front and note that you did. Length is the second-heaviest input in the fit score, after chest.

You have probably arrived here wanting to measure your own shoulders. Quickly, then: stand relaxed, have someone run a tape across your back from the bony point of one shoulder to the other. That number is real, but it is not what picks a shirt.

The garment number is, and it is the one below. A shirt’s shoulder seam can sit inboard of your shoulder point, on it, or well past it, and the same body measures well in all three — that gap is the cut, and no body measurement recovers it. Body versus garment measurement explains why the garment wins.

The definition: “Across the back, from the top of one shoulder seam to the other.”

Where the tape goes. Flip the shirt face down. Measure across the back from the point where one shoulder seam meets the sleeve to the same point opposite.

The common mistake. Measuring across the front, where the collar sits lower and the tape drifts off the seam points. On a raglan sleeve this point does not exist at all — leave it blank rather than inventing an endpoint.

The definition: “From the shoulder seam down the outside of the sleeve to the cuff edge.”

Where the tape goes. Start where the shoulder seam meets the sleeve, follow the outer fold, and stop at the far edge of the cuff or sleeve hem.

The common mistake. Assuming every brand means that. They do not, and the disagreement is large enough to change what you buy — some measure from the centre of the back of the neck instead, which produces a number roughly twice as big for the same shirt. Because this one point needs its own page, it has one: how to measure sleeve length sets out both conventions and which brands use which.

Most people looking this up want to measure their arm: flex or relax as you prefer, wrap the tape around the fullest part, keep it level, read the circumference. That is your bicep.

The shirt’s bicep is a different quantity and it is the one that predicts whether the sleeve binds. It is a flat width across the sleeve, so it is roughly half your arm circumference plus whatever ease the pattern maker left. Compare like with like or the sleeve will surprise you — see body versus garment measurement.

The definition: “Across the sleeve, 1" below the armhole, laid flat.”

Where the tape goes. With the sleeve unfolded and lying in one plane, measure across it one inch below where it joins the body, from the outer fold to the underarm seam.

The common mistake. Measuring mid-sleeve, where the taper has already narrowed it, or over a creased sleeve. The scanner names bicep one of its two least reliable readings, so re-tape a scanned bicep that looks odd.

The definition: “Straight across the cuff opening, laid flat.”

Where the tape goes. The width of the sleeve’s exit — the cuff of a long sleeve, the hem of a short one. Arrange the opening flat in one plane and measure edge to edge across it.

The common mistake. Measuring around the opening, which doubles the number, or pulling a ribbed cuff taut. Let the rib rest at its natural width. This is the scanner’s other least reliable reading, so check it by hand as well. It carries the smallest weight in the fit score, which makes it the one to leave blank if you are only taking a few.

On a straight-cut tee these are the same measurement, and ShirtMath records it once, as sweep. The shirt has no separate waist to find: the side seams run essentially straight, so the narrowest point and the bottom opening are the same line.

On a tapered shirt they part company. There the waist is the narrowest point of the body, usually a few inches above the hem, and the sweep is still the opening at the very bottom. If you are measuring a fitted dress shirt, take both and label them; if you are measuring a tee, take the one and do not invent the other.

The definition: “Straight across the bottom opening, laid flat.”

Where the tape goes. Across the very bottom of the shirt, edge to edge at the hem.

The common mistake. Measuring an inch or two above the hem, where a tapered side seam has already pulled in. Measure the opening itself. Read against the chest, the sweep tells you the body shape: a sweep close to the chest is a near-straight tube, a sweep well under it is a taper.

If you came here for your collar size — the 16 in a dress-shirt size like 16 34/35 — that is a body measurement: the circumference around your neck, taken with one finger of slack. It is a different system, and the dress shirt size chart speaks it.

What ShirtMath records is the garment’s neck opening, a flat width. It is not a collar size and the two numbers will never match; comparing them is the classic version of the mistake body versus garment measurement is about.

The definition: “Across the inside of the collar, seam to seam.”

Where the tape goes. Straight across the inside of the collar, from one seam edge to the other where the collar joins the body.

The common mistake. Taping the collar’s outside edge, which adds the band width at both ends.