Flat Cap Sizing and Fit Guide

How to measure correctly, navigate brand differences, and fix a cap that doesn't fit right.

Flat cap sizing is not standardized. A medium from one brand might feel like a large from another, and the difference between a cap that sits perfectly and one that slides around or pinches your forehead often comes down to a single centimeter. Whether you are buying your first cap or your fiftieth, understanding how to measure your head, read a sizing chart, and adjust fit after the fact will save you money and frustration.

How to Measure Your Head

All you need is a flexible measuring tape and a mirror. If you do not have a fabric tape, use a piece of string and then measure the string against a ruler.

1. Stand in front of a mirror. You will want to see the tape position from the front and sides as you wrap it.
2. Place the tape about one inch above your eyebrows. This is where the front of a flat cap will rest. The tape should sit on the slight ridge above your brow line, not on your forehead or hairline.
3. Wrap the tape around the widest part of the back of your head. Guide it just above your ears on both sides, keeping it level all the way around. The tape should pass over the occipital bump at the back of your skull, which is the widest point for most people.
4. Keep the tape snug but not tight. You should be able to fit one finger between the tape and your skin. If the tape is compressing your skin, you are pulling too hard. If it sags or droops at any point, it is too loose.
5. Read the measurement where the tape overlaps. Round up to the nearest half centimeter. This is your head circumference, and it is the number you will use when consulting any sizing chart.

Sizing Systems Explained

Flat caps are sold using several different sizing systems depending on the brand and region. US sizes are numerical (usually fractions like 7 1/4), UK sizes follow a similar scale but with different numbers, and many European and Irish brands use S/M/L or centimeter measurements. The table below maps these systems to each other so you can convert between them.

How Different Brands Run

Even with accurate measurements, you may find that certain brands consistently run larger or smaller than their labeled size. Here is what collectors generally report:

• Boston Scally — True to size. If you are between sizes, go with the larger one. Their elastic sweatbands are forgiving and will conform to your head within a few wears.
• Stetson — Runs large. Many collectors find they need to go down a size from their measured fit, especially in the linen and cotton styles.
• Kangol — Varies by style. The 504 tends to run slightly small, while the Tropic and Bermuda lines are more generous. Check the specific style rather than relying on a single Kangol size across the board.
• Hanna Hats — Runs small. Irish-made caps from Hanna tend to fit snugly. Size up if you are between sizes, and expect a brief break-in period before the wool relaxes.
• Failsworth — True to size. Failsworth uses consistent sizing across most of their range. Their wool and tweed caps hold their shape and size well over time.
• Christys' — True to size. As one of the oldest hat makers in England, their sizing is reliable. The internal leather sweatbands give a precise fit that does not change much with wear.

What to Do if Your Cap Is Too Tight

A cap that pinches your forehead or leaves a red mark is too tight, but that does not mean you need to return it. There are several safe ways to stretch a flat cap by a small amount, usually up to about one centimeter.

• Hat stretcher (recommended). A wooden or plastic hat stretcher lets you apply gradual, even pressure to expand the sweatband and body of the cap. Insert it, turn the knob until you feel light resistance, and leave it overnight. Repeat over a few days if needed. This is the safest method and gives you the most control.
• Damp method. Lightly mist the inside of the sweatband with water, then place the cap on your head or on a round object slightly larger than your head size, such as a bowl or melon. Let it dry completely in that stretched position. The moisture loosens the fibers just enough to allow a gentle stretch without damaging the fabric.
• Steam stretching. Hold the inside of the cap over steam from a kettle for 15 to 20 seconds, then immediately place it on your head or a hat stretcher. The heat and moisture soften the fibers temporarily. Be careful not to over-steam wool or tweed, as excessive heat can shrink or warp the material.

What to Do if Your Cap Is Too Loose

A loose cap that shifts around or slides forward is just as annoying as one that is too tight. Fortunately, it is easier to make a cap smaller than to make it bigger.

• Hat sizing tape. Self-adhesive foam strips designed to go inside the sweatband of a hat. They add thickness to the interior, effectively reducing the circumference by a few millimeters per strip. You can layer them for a bigger adjustment. This is the cheapest and most reversible fix available.
• Wool wash method. If your cap is made of wool or tweed, a careful hand wash in warm water can tighten the fibers slightly. Submerge the cap in warm (not hot) water with a small amount of wool-safe detergent, gently press it for a minute or two, then reshape it and let it air dry on a rounded surface. Do not use a dryer. The warmth causes minor felting that can reduce the cap by half a size.

Breaking In a New Cap

Most flat caps need about five to ten wears before they truly feel like yours. The sweatband will soften and conform to the shape of your head, the brim will develop a natural curve that matches how you position it, and the overall fit will settle into something more comfortable than what you felt on the first try. Wool and tweed caps benefit the most from a break-in period. Cotton and linen caps tend to feel closer to their final fit right out of the box.

During the break-in period, resist the urge to reshape the cap aggressively. Just wear it. Walk around the house, run errands, take it on a weekend outing. The natural heat and moisture from your head will do the work for you.