What Is a Shirt for Men? | Sizing That Actually Fits

Buying a shirt without knowing your numbers is a gamble. The difference between a sharp fit and a sloppy one comes down to three measurements: your neck, your chest, and your sleeve length. Most men guess their size based on a letter — and end up with a collar that strangles or a hem that rides up. Here’s what those sizes actually mean and how to measure yourself in under five minutes.

How Men’s Shirt Sizes Work in US Retail

US retailers use two overlapping systems. Casual shirts and T-shirts rely primarily on chest circumference, while dress shirts lean on neck and sleeve measurements. Both systems map to letter sizes, but the underlying numbers are what matter.

ASOS’s US men’s size chart spans XXXS to XXXL, pairing each letter with a chest and neck range.

Brands like Aeropostale and Primark follow the same logic with slight variations. The takeaway: letter sizes are loose buckets, not universal truths.

The Three Measurements That Decide Your Fit

Getting your numbers right takes two minutes with a cloth tape measure. Nike’s guidance is the standard: measure your chest around the fullest part, your waist around the narrowest part, and your hips around the fullest part, keeping the tape level.

The neck and sleeve are where dress shirts live or die. C&A instructs measuring the collar around the neck at the Adam’s apple, keeping it loose, and adding about 1 cm. OPPOSUITS uses the same base-of-neck approach and adds that sleeve length applies to long-sleeved shirts specifically. For the waist, C&A suggests measuring at the belly button and adding 5 cm for breathing room.

Here’s the distinction that trips most guys up: a T-shirt fits by chest, but a dress shirt fits by neck and sleeve. Use T-shirt logic on a button-down and you’ll get a collar that cuts off circulation.

Why the Letter Size Is Never the Whole Story

Size labels are not standardized across retailers. A large at one store can fit like a medium at another. That’s why every reputable chart — from ASOS to Saks — maps letters to physical measurements rather than asking you to trust the letter alone.

Two mistakes cause most return trips. First, measuring the neck too tightly; both C&A and OPPOSUITS explicitly warn against this. Second, ordering a dress shirt off chest size only, which ignores the collar and arm length entirely. A shirt can fit your torso perfectly and still fail on both counts.

Sleeve charts differ between short and long sleeves, so check which one you’re reading. And if you’re between sizes, size up for a relaxed fit or size down for a trim one — but always verify against the specific brand’s chart first.

Once you have your measurements locked in, the hard part is done. If you’re shopping for undershirts, our tested roundup of the best A-shirts for men breaks down which ones hold up wash after wash.

Compiled from ASOS, Saks Fifth Avenue, and Primark men’s size charts. Always confirm against the specific brand’s current chart.

Measure Once, Buy Right Every Time

Write your three numbers down — neck, chest, and sleeve — and keep them on your phone. Those figures, not the letter on the tag, are what make a shirt fit. Compare them against each brand’s chart before you order. When they match, the shirt fits. When they don’t, the shirt goes back.

That habit turns buying shirts from a guessing game into a routine. ASOS’s men’s size chart is a solid reference point to see how measurements map across sizes. One good set of numbers works for every retailer you’ll ever shop.