Hat Size Calculator

How the crown shaping is figured

This treats the hat as a cylinder (the straight body) topped with a flat circle (the crown). The crown's depth is estimated from its radius, so the calculator subtracts that from your total height to get how far to work straight before the crown shaping. It's an approximation — heads aren't perfect cylinders — but it's a solid starting plan that you can adjust by trying the hat on as you go. Use the Construction menu to build the crown first (top-down) or last (bottom-up).

Why negative ease matters more than it seems

Crocheted fabric has far less natural stretch than knit fabric, so a hat made to your exact head circumference will usually feel loose and slip down rather than sitting snugly. A stretchier stitch (like a ribbed post-stitch pattern) can get away with less negative ease than a stiff, dense stitch worked in worsted-weight cotton, which barely stretches at all — if you're working in a non-stretchy stitch, consider using 1.5 to 2 inches of negative ease rather than the default 1 inch here.

Adjusting for a folded brim

If you plan to fold up a cuff or brim at the bottom edge, add the doubled height of that fold to your total hat height before calculating — a 2-inch folded cuff needs 4 extra inches of fabric, not 2, since it folds back on itself. Skipping this is a common reason a finished hat ends up shorter than expected once the brim is folded into place.

The decrease plan here uses a standard spiral or joined-round crown, decreasing evenly around each round. Some patterns instead cluster all the decreases for a round into one section (a "pie slice" crown) — both approaches use the same total stitch count, but a pie-slice crown can pull slightly off-center if your tension varies through the round, so an evenly distributed decrease is usually the safer default for a first attempt at a size.

How to Make a Hat That Actually Fits

Hats are the classic first "real" project because they're small, fast, and need no seaming. They're also the project most often made an inch too big, which turns a hat into something that slides down over the eyes. Fit comes from two decisions — circumference and depth — and both are easy to get right if you know what number you're aiming at.

Step 1: Measure the head

Run a tape measure around the head at its widest point: across the forehead just above the eyebrows, above the ears, and around the fullest part of the back of the skull. Keep it snug. If you're making the hat as a gift and can't measure, use the averages below.

Size	Head circumference	Hat depth (crown to brim)
Newborn	13–14 in	5.5 in
Baby, 3–6 months	15–17 in	6.5 in
Toddler	18–19 in	7.5 in
Child	19–20 in	8 in
Adult small / teen	20–21 in	8.5 in
Adult medium	21–23 in	9 in
Adult large	23–24 in	9.5 in

Step 2: Subtract for negative ease

This is the step that separates a hat that stays on from one that doesn't. A hat needs to be smaller than the head so the fabric stretches slightly and grips. Make it the actual head measurement and it will slip.

Subtract 1 to 2 inches from the head circumference and use that as your target hat circumference. Use the smaller subtraction for a stiff, dense fabric with little give, and the larger for ribbing or a stretchy stitch. The calculator above applies this and converts it to a stitch count at your gauge.

Step 3: Decide top-down or bottom-up

Direction	How it works	Good for
Top-down (crown first)	Start with a magic ring, increase as a flat circle until it's wide enough, then work straight down.	Crochet, and any hat where you want to keep trying it on for depth.
Bottom-up (brim first)	Cast on the brim, work up the body, then decrease the crown.	Knitting, and anything with a ribbed brim.

Step 4: Get the crown right

Working top-down, the crown is a flat circle, and the question is when to stop increasing. The answer: stop when the circle's diameter reaches roughly one third of your target circumference — more precisely, circumference divided by pi. For a 20-inch hat that's about 6.4 inches across. Then stop increasing and work straight down for the depth.

Measure the circle flat with a ruler rather than guessing. Increasing one round too long gives a hat with a flared, beret-like top; stopping one round early gives a pointed crown that stands up off the head.

Working bottom-up, the crown decreases mirror this — spread your decreases evenly around, and see the evenly spaced calculator for the distribution.

Step 5: Work the depth

Use the depth from the table, measured from the top of the crown to the brim edge. A hat that's too shallow rides up and looks perched; too deep and it swallows the ears. If you want a slouchy hat, add 2 to 3 inches to the depth and keep the circumference the same — slouch comes from extra length, not extra width.

Step 6: Brim

Ribbing is the standard finish because it pulls in and grips. In crochet, front-post and back-post double crochet alternated gives a convincing rib; in knitting, k1p1 or k2p2. Work the ribbing on a smaller hook or needle than the body to tighten it further.

For a folded brim, double the brim length — if you want a 2-inch folded cuff, work 4 inches of ribbing. Remember to account for that fold in your total depth, or the finished hat comes out two inches shorter than planned.

Common problems

Problem	Cause and fix
Hat slides down over the eyes	No negative ease. Subtract 1–2 in from head circumference.
Top flares out like a beret	Increased too many rounds. Stop when the circle's diameter is circumference ÷ pi.
Crown comes to a point	Stopped increasing too early. Add a round or two.
Too tight and leaves a mark	Too much negative ease, or a non-stretchy fiber. Cotton and acrylic have less give than wool.
Brim won't stay folded	Ribbing too loose. Go down a hook or needle size for the brim.
Hat is shorter than planned	Fold not accounted for. Double the brim length for a folded cuff.

Related Calculators