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How to Read and Convert Dress Shirt Collar Sizes

A dress shirt collar size is just your neck circumference expressed in one of two unit systems β€” the tricky part is measuring it correctly and knowing that the same number does not fit identically across every brand.

Collar size is neck circumference, not a generic garment size

Unlike a shirt's overall size label (like Medium or Large), a dress shirt collar size directly corresponds to the measured circumference of the wearer's neck at the point the collar sits.

Inch-based sizing (common in the US and UK)

Neck circumference in inches, typically in half-inch increments β€” 14, 14.5, 15, 15.5, up to around 18-19 for larger sizes β€” with the number referring directly to the measured neck size in inches, plus a small amount of built-in ease.

Centimeter-based sizing (common across the EU, Japan, and China)

Neck circumference in centimeters, typically in even numbers β€” 37, 38, 39, 40, 41, 42, and so on β€” following the same underlying logic as inch sizing, just expressed in the metric system.

Conversion formula: inches Γ— 2.54 = centimeters

A 15.5-inch collar converts to roughly 39.4 cm, which typically rounds to a 39 or 40 cm labeled size depending on the brand's specific rounding convention β€” there is no single universal rounding rule across brands.

Measure with slack for comfort, not a tight circumference

A common method is wrapping a tape measure around the base of the neck and leaving room for one or two fingers between the tape and the neck, since a shirt collar measured to an exact skin-tight circumference will feel too snug once buttoned.

Collar size alone does not determine overall fit

Sleeve length is typically sized separately, often shown as a second number (like 15.5/34, meaning a 15.5-inch collar with a 34-inch sleeve), and the overall cut (slim, regular, or classic) affects body fit independently of the collar number.

How to measure neck size correctly

Wrap a soft measuring tape around the base of the neck, roughly where a buttoned collar would sit, and slide one to two fingers between the tape and the skin before checking the measurement β€” this "finger test" approximates the small amount of ease a comfortable collar needs. Measuring too tightly is the most common source of buying a collar size that feels constricting once worn for a full day.

Why the same collar number can fit differently across brands

Collar size is standardized enough to be broadly comparable, but garment cut is not: a slim-fit shirt and a classic-fit shirt in the same labeled collar size often differ noticeably in how the collar and body actually sit, since manufacturers apply their own ease and pattern adjustments on top of the base measurement. Checking a specific brand's size chart, rather than assuming a number translates identically everywhere, avoids most fit surprises.

Frequently Asked Questions

When converting inches to centimeters, should I round up or down?

There is no single universal rule β€” it depends on the brand's sizing chart. When a converted measurement falls between two standard sizes, many general guides suggest sizing up slightly for comfort, but checking the specific brand's chart is more reliable than assuming a fixed rounding convention.

Is collar size enough information to buy a well-fitting shirt?

Not by itself. Collar size only measures neck circumference; sleeve length and the shirt's overall cut (slim, regular, or classic) both affect fit significantly and are specified separately, so relying on collar size alone can still result in a shirt that fits oddly elsewhere.