How to measure your shoulder width

Shoulder width is measured seam-point to seam-point across the back

With arms relaxed at your sides, measure straight across the back from the bony point of one shoulder (where a jacket seam would naturally sit) to the identical point on the other shoulder — a straight line across the back, not following the curve of the shoulders down and around.

Finding the correct seam point on your own body

The bony point at the edge of the shoulder, just before the arm begins, is generally where a well-fitted jacket's shoulder seam sits — feeling along the top of your shoulder from the neck outward, the point where it starts to slope down toward the arm is the landmark to measure to.

This measurement needs a helper more than most others on this site

Because shoulder width is measured across your own back, a spot you genuinely can't see directly, having someone else take this measurement is considerably more reliable than attempting it alone with a mirror — of all the measurements on this site, this is the one where a second person adds the most accuracy.

Stand relaxed, not deliberately squared up

Stand in your natural, relaxed posture with arms at your sides rather than deliberately pulling your shoulders back into a squared, military stance, since an artificially straightened posture changes the shoulder width reading away from how you naturally stand and wear clothes day to day.

Shoulder width feeds directly into suit, shirt, and coat sizing

This figure matters most for structured, tailored garments — suits, dress shirts, and structured coats — where shoulder seam placement is a visible, hard-to-alter fit point, unlike a chest measurement alone which a garment's ease allowance can partially absorb.

An ill-fitting shoulder is one of the hardest things to alter after purchase

Unlike hemming a sleeve or taking in a waist, re-positioning a garment's shoulder seam is a major, expensive alteration that many tailors avoid or discourage — getting this measurement right before ordering matters more than for almost any other figure on a structured garment, since a wrong shoulder fit is difficult and costly to fix after the fact.

Athletic and broader builds may need shoulder checked against chest independently

As covered on the chest measurement guide elsewhere on this site, an athletic or broader-shouldered build can have a shoulder measurement that suggests sizing up beyond what the chest figure alone would indicate — checking both figures together, rather than chest in isolation, catches this before ordering a jacket that binds across the back.

Common measuring mistakes that throw the shoulder-width number off

• Measuring alone without a helper, using a mirror as an imperfect substitute
• Squaring the shoulders into an unnatural, deliberately straightened posture
• Measuring along the curve of the shoulder rather than in a straight line across the back
• Confusing the bony shoulder edge with a point further out on the arm
• Treating shoulder width as less important than chest for a structured jacket

A well-fitting existing structured jacket can serve as a reference

A jacket you already know fits well can double as a stand-in ruler: button it, lay it flat, and measure seam to seam across the back panel — if that number lands close to what you measured standing up, trust the body measurement; a big gap between the two is worth investigating before you rely on either figure.

Drop-shoulder and raglan styles use shoulder measurement differently

A deliberately oversized drop-shoulder style or a raglan-sleeve garment (where the sleeve seam runs to the collar rather than a defined shoulder point) doesn't reference shoulder width the same precise way a tailored jacket does, since these styles are designed without a fixed shoulder seam point at all — this measurement matters most for structured, tailored garments specifically, less for these looser, seamless-shoulder styles.

Shoulder width interacts with arm length in a way worth checking together

Because sleeve length is typically measured from the shoulder point outward, an inaccurate shoulder-width reading can throw off where a garment's arm-length measurement effectively starts from, so checking shoulder width and the separate arm-length guide together, rather than treating them as fully independent figures, gives a more coherent overall picture for a tailored garment.

Photographs of yourself in well-fitted jackets can help validate a measurement

Comparing your measured shoulder figure against how a jacket you know fits well actually looks in a photo — where the shoulder seam visibly sits relative to your actual shoulder edge — gives a useful sanity check that a number alone doesn't provide, particularly useful when a helper isn't available to measure you directly.

Women's structured jackets and blazers use the same measurement principle as men's

The core method described throughout this guide — seam point to seam point, straight across the back, relaxed natural posture — applies identically whether you're converting a men's suit jacket size or a women's structured blazer size, since both garment categories rely on the same shoulder-seam construction logic.

A too-tight tape measure across the back distorts the reading more than elsewhere

The skin and muscle across the back have less give than the front torso does, so pulling the tape even slightly taut across the shoulders compresses the reading in a way the same tension wouldn't at the chest or waist. Let the tape follow the natural curve loosely rather than pulling it into a straight line.

Recording shoulder width alongside chest keeps a complete jacket-sizing reference

Because suits, shirts, and coats all reference chest and shoulder together, keeping both figures recorded side by side — rather than shoulder as an isolated, easily-forgotten number — makes checking a new international brand's jacket chart faster and reduces the chance of ordering against only one of the two relevant figures.

Kids' structured jackets and school blazers use the same measuring principle at a smaller scale

For a child's formal jacket or school blazer, the identical seam-to-seam back measurement applies, though a helper is even more essential given how much harder it is for a young child to hold a relaxed, natural posture still long enough for an accurate reading — patience and a couple of attempts often produce a more reliable number than rushing a single try.

A recently worn backpack or bag strap can distort a self-measured reading

Carrying a bag or backpack, even for a short walk beforehand, can leave your shoulders held in a slightly hunched or uneven position for a few minutes afterward without you consciously noticing, which shifts where the tape actually sits relative to your natural resting posture — taking this measurement after sitting or standing normally for a few minutes without a bag on, rather than immediately after removing one, gives a more representative reading.

A recently slept-on or awkward sleeping position can leave temporary shoulder stiffness that skews a reading

Waking with a stiff or favored shoulder from an awkward sleeping position can lead to an unconsciously uneven stance for the first hour or so of the day, similar in effect to the bag-strap distortion covered above, so measuring later in the day once any morning stiffness has worked itself out tends to give a more representative, symmetrical reading.