How should a hat fit?

Seen from the side, the band of a brimmed hat runs almost level: across your forehead about a finger above your eyebrows, about a finger above the tops of your ears, and around the bump at the back of your skull. It should touch your head all the way round with light, even pressure.

Depth is the second check. The crown has to come down far enough that the hat sits on your head rather than on top of it. If you see daylight between the band and your temples, or the hat rises when you look up, the crown is too shallow for you or the size too small.

Angle comes last and is partly a matter of taste. Most brimmed hats look best level or tipped slightly forward; a trilby is worn a little back, a beret to one side, a cloche down to the brows. A cap sits with its peak straight ahead and its back strap above the ridge at the base of your skull.

A hat that is too small rides up. It sits high and looks perched, and it creeps upward every time you raise your eyebrows. After half an hour the band presses a line into your skin, and the pressure turns into a dull ache at the temples or across the forehead.

On a felt or straw hat the sweatband looks strained and the brim may tip up at the back, because your head is forcing the hat open. A fitted cap that is too small bulges at the panels, an adjustable one ends up on its last hole, and a beanie slides up off your ears within minutes.

There is not much you can do about it. Soft felt can be eased about a quarter size by a hatter with steam and a stretcher. Straw and hard felt barely give, and a fitted cap gives nothing, so those go back for the next size up.

A hat that is too big drops toward your eyebrows and the tops of your ears, turns when you turn your head and lifts off in a gust of wind. From the front it can look as if the hat is wearing you, with too much crown above a face that seems to shrink beneath it.

Run a finger round the inside of the band while you wear it. If there is room for more than a finger at the sides and the back, the hat is loose. A little too big is still the better mistake, because a loose hat is easy to take in.

Sizing tape, a self-adhesive foam strip stuck behind the sweatband, takes up the slack in a hat that is up to about a size too big. Spread it evenly around the band so the hat still sits level. Beyond that, the tape changes how the hat sits, and a smaller size will fit better than a padded one.

Seen from above, every head is an oval, but not the same oval. Two people with the same circumference can have a long, narrow head or a short, broad one. A hat blocked for an average oval presses at the front and back of a long head while gaping at the sides, and does the opposite on a round one.

Hatters speak of long oval, regular oval and round oval fits, and some makers say which one they cut. If a hat in your measured size pinches in two places and gaps in two others, the shape is the problem, not the size: try another maker, or have a hatter shape a felt hat to your head with steam.

Every material forgives a different amount, so the size that is right in one hat can be wrong in the next. These six cover the main cases, from a cap that adjusts to a hat that gives nothing.

Once a hat fits, look at it in a full-length mirror, not just in a close-up. A brim a little wider than your face looks balanced on most people, and a tall or broad frame can carry more. A narrow brim on broad shoulders makes the head look small; a very wide one on a slight build takes over the whole outline.

Crown height works on the face. A taller crown makes a short or round face look longer, while a lower crown keeps a long face in balance. The pages on hats for big heads, hats for small heads, hats for a round face and hats for an oblong face go into the details, and the guide to hat styles shows which crowns and brims each style has.

In a shop, wear the hat for a few minutes before you decide. Look down at your feet and up at the ceiling, turn your head quickly, and check the back in a second mirror. A hat that fits well feels like nothing after five minutes; one that you keep noticing will not get better.

Online, shop by inches or centimeters rather than by S, M and L, because letter sizes shift from one maker to the next. Hold the maker's chart against a hat you own that fits, and check the return policy before you order a size you have never worn. Our hat size calculator gives you your US and letter size from one measurement.

Whichever way you buy, measure with your hair the way you will wear it under the hat, and measure twice. Thick hair worn loose can add a quarter inch or more to the number; a fresh short haircut can take it away.