Driving Cap Sizing Guide: How to Find Your Fit | Measure Once, Order Right

Measure around the head at the actual hat line, then match that number to the manufacturer’s own size chart, because a labeled medium varies from one maker to the next.

A wool driving cap that shifts forward while you’re steering is a nuisance, and one that pinches leaves a red band across your forehead by noon. Getting the fit right starts with a single tape reading taken in the right spot — not the “medium” label you wore in a baseball cap. The steps below take about a minute, and the size chart farther down translates your number into a real order.

How Do You Measure For A Driving Cap?

Wrap a flexible tape measure around the head where the cap will rest — level across the forehead and just above the ears — and write the number down in both inches and centimeters.

Work through it in this order:

1. Use a soft tailor’s tape. If you only have string, wrap it, mark the overlap, then lay it flat against a ruler.
2. Set the tape roughly 2 cm above the ears, crossing the middle of the forehead and the temples. That’s the hat line, and measuring anywhere else skews the result.
3. Keep the tape level all the way around — flat at the back, not riding up over the crown.
4. Snug it until it sits firm against the skin without pressing in. A loose tape reads small; a tight one reads large.
5. Note the circumference in inches and centimeters, then check it against that specific cap’s chart.

Repeat it once. If the second reading differs from the first by more than an eighth of an inch, take a third and use the middle figure.

What Size Cap Does Your Measurement Match?

Compare your head circumference against the maker’s chart, then convert into the driver-cap size group that chart uses, since brands break their ranges slightly differently.

The table below runs from the smallest to largest adult sizes and pairs head circumference with hat size, metric size, and the typical driving-cap letter.

Treat those numbers as a starting frame, not gospel. Pendleton’s sizing for its Classic Wool Driving Cap lands a 21½-inch head in a small 6¾, while other makers put that same circumference a fraction higher. Nordstrom’s waxed-cotton chart maps 57 cm to roughly a 7, 59 cm to 7¼, and 61 cm to 7½ — the same metric numbers sitting on slightly different hat sizes. That drift is why the product page’s own chart always wins.

When you’re ready to pick a material, the tested wool driving cap roundup narrows the field by fit and construction.

What If Your Measurement Falls Between Sizes?

Go up, not down. Manufacturers generally recommend sizing to the larger option when you land between two, and a driving cap has no laces to tighten on arrival.

A close-fitting brand might still work a half size down, but that’s a gamble. The safer move is the next size up — often rounding to the nearest eighth of an inch in that direction — then snugging the fit with sizing tape tucked behind the sweatband. Felt pads work the same way for head shapes that sit oddly between two measurements.

Fitting at the sweatband is what actually matters. A cap should hold steady without pressing. Too loose and it slides while you drive; too tight and you’ll feel it within an hour. Tug the cap gently when it arrives — if the band grips without squeezing, the size is right.

One more thing worth saying plainly: these are fashion caps. None of the manufacturer material treats a driving cap as protective headgear, and a flat cap is no substitute for a legal motorcycle or motorsport helmet.

Which Measurement Mistakes Cost You A Return?

The four that show up most: measuring around the crown instead of the hat line, holding the tape slack or hauled too tight, assuming a 59 cm from one brand equals a 59 cm from another, and ordering the smaller size when the number straddles two.

The brand-to-brand assumption is the expensive one. A centimeter figure is not a universal constant across labels — construction and chart conventions differ. Some charts blur US hat sizes with metric sizes, and one listing openly warns that the sizing can confuse buyers. Check the chart printed on the exact product page before you commit.

Skip the hope that an adjustable or stretch cap in one size will behave like a fitted one. The brands reviewed here don’t publish a single universal range for those, so there’s no reliable shortcut.