New Era cap sizing guide: 59FIFTY vs 39THIRTY vs 9FORTY

New Era caps are the reason most people learn that "7 1/8" is a hat size at all. The brand built fitted baseball caps around the same head-measurement math as any traditional hatter, then layered three fit systems on top of one head range. This guide explains all three of the brand's flagship models — the 59FIFTY, 39THIRTY and 9FORTY — how their sizes relate to one another, and how to turn one tape measurement into the right cap. For the full numeric tables, see our New Era sizes breakdown (unofficial).

Three fit systems, one head range

• 59FIFTY — fitted. The pro-style flagship and the baseball hat size chart standard: a structured crown, a flat visor, an enclosed ear-to-ear band and sizes in eighth-inch fractions from roughly 6 7/8 to 8. It stretches slightly? Not at all — the fit is exactly what the number says.
• 39THIRTY — stretch-fit. A lower-profile crown and a visor that curves to meet it. Sizes come in combined spans (S/M, M/L, L/XL, XL/2XL), each one covering three to four fitted fractions by relying on an elastic headband.
• 9FORTY — adjustable. The strapback silhouette. One shell size fits a range of heads thanks to an adjustable closure; the relevant "size" becomes crown depth and the position of the strap, not circumference.

All three silhouettes cover roughly the same span of adult heads — about 54 to 63 cm — but they get there differently. On a 59FIFTY the number is the fit; on a 39THIRTY the number is a range; on a 9FORTY the number is a starting point that the strap adjusts around.

How the numbers work

The brand's fitted fractions are the cast of the traditional hat size chart, not a separate system. Take your head circumference in inches and divide by pi: the result is your head's diameter, and that — rounded to the nearest eighth of an inch — is the size printed inside the sweatband. A 23 1/8 inch (58.7 cm) head works out to a US fitted 7 3/8, which is exactly what the fraction on the label means. The fitted cap size chart lists every fraction with its cm, inch, UK and EU equivalents.

One nuance: New Era caps — and MLB on-field caps generally — are cut slightly round and a touch roomier than a traditional brimmed hat of the labeled size. When a raw tape number would land between two fractions, players typically take the smaller fraction for the 59FIFTY's structured feel, while streetwear wearers often go up. Treat that as a preference, not a sizing rule; the chart remains the baseline.

Measure once, wear any silhouette

The whole point of understanding the systems is that one measurement serves every cap the brand sells:

1. Wrap a soft tape around your head just above the ears, level across the forehead — full details in our measuring guide.
2. Enter the number in the hat size converter to get every equivalent at once.
3. Buy a 59FIFTY two-to-three eighths under the raw stretch-fit midpoint only if you prefer a snug structured fit; buy a 39THIRTY span that contains your fraction straight from the mapping table.

Choosing between 59FIFTY and 39THIRTY

If your head sits near the middle of a stretch-fit span, a 39THIRTY will feel close to the fitted sizing with built-in forgive-the-heat-mornings elasticity. If your head sits near a fraction boundary — for example 58.0 cm, which is nearly equidistant from 7 1/4 (57.8 cm) and 7 3/8 (58.7 cm) — the fitted-crown 59FIFTY rewards decision more than the elastic one does: there you must choose the fraction by fit feel, whereas the 39THIRTY M/L span absorbs the choice for you. Kids' heads are a different market segment again until they cross roughly 53 cm; before that, use a dedicated youth table such as our youth hat size chart.

Breaking in and keeping fit

A 59FIFTY relaxes about a quarter of a size over its first weeks of wear — sweat and body heat soften the band. Adjust expectations accordingly when trying on in-store: a fresh cap should feel firmly snug, never loose. Between washes (caps are spot-clean, cold water only by the way), store the crown stuffed so the canvas holds its shape. If a cap loosens over years of wear, a strip of hat-sizing tape inside the band takes up the slack — and if everything about your fit keeps feeling wrong, re-measure; haircuts and cold weather genuinely change the number.

Measure, convert, then pick a silhouette: that's the entire decision. Everything else is style — and prices.