Hat Crown Decrease Planner
A baby hat and an adult hat decrease at the same rate per round — the circumference cancels out. Plan the crown from your own gauge.
| Round | Work | Stitches left |
|---|
A baby hat and an adult hat decrease at the same rate
This is the part that sounds wrong and is not. The crown of a hat is a flat circle worked backwards, and the arithmetic falls out in one line. A crown that closes a hat of circumference C is a disc of radius C/2π. At h per round it takes C/(2π·h) rounds, and over those rounds all C/w stitches have to disappear. Divide one by the other:
decreases per round = 2π · h / w
The circumference cancels. It is gone. A 16-inch baby hat and a 24-inch adult hat lose the same number of stitches per round at the same gauge — the big hat simply spends more rounds doing it. Sweeping every head size from 14 to 26 inches moves that rate by nothing at all, and it is the same constant that governs the increase side of a flat crochet circle. One formula, two crafts, opposite directions.
Which is why "decrease every other round" advice travels so badly between patterns. The rate is not a style choice and it is not a function of the size; it is set by how tall your rounds are relative to how wide your stitches are, and nothing else.
Choose the brim for its divisors, not for the tape measure
A crown decreases in wedges, so the section count has to divide the brim exactly. Cast on a nice round 100 and you have quietly ruled out every 6-section and 8-section crown there is — 100 takes 4, 5 and 10 and nothing else in the usable range. Cast on 96 or 120 and you can have any of them.
| Brim stitches | Section counts available | |
|---|---|---|
| 88 | 4, 8, 11 | workable |
| 90 | 5, 6, 9, 10 | plenty of choice |
| 96 | 4, 6, 8, 12 | plenty of choice |
| 100 | 4, 5, 10 | workable |
| 104 | 4, 8 | restrictive — check before casting on |
| 108 | 4, 6, 9, 12 | plenty of choice |
| 112 | 4, 7, 8 | workable |
| 120 | 4, 5, 6, 8, 10, 12 | plenty of choice |
At four and a half stitches to the inch, moving from 100 to 96 costs you under nine tenths of an inch of brim — well inside the stretch of any ribbing and far inside the range of heads a hat has to fit. It buys the entire crown. Decide this before you cast on, because afterwards the only fixes are decreasing unevenly or fudging a round.
What the plan assumes
- A flat-topped crown. The rate above closes the hat as a disc, which is the shape most patterns want. A deliberately rounded or beret crown decreases more slowly at first and faster at the end, and takes more depth to do it.
- Negative ease is doing real work. A hat knitted to the size of a head does not stay on one. Two inches is a normal figure for ribbing; a non-stretchy fabric wants less, a wide rib wants more.
- Ribbing measures smaller than it wears. Take gauge in the stitch the body is worked in, not over the brim — a rib relaxed on the needle and a rib on a head are different fabrics.
- Round the last rounds by feel. The plan stops when the remaining stitches are few enough to gather; cut the yarn, thread it through the live stitches and pull. Chasing the arithmetic to zero leaves a nipple on the top of the hat.
How to use
- Enter the head circumference and how much smaller the hat should be.
- Add your gauge and the finished height you want.
- Pick a section count from the ones your brim actually divides by.
- Work straight for the rounds shown, then follow the crown plan.
Frequently asked questions
When do I start decreasing a hat?
When the remaining height equals the crown radius, which is the circumference divided by 2π. For a 20-inch hat that is 3.18 inches from the top, regardless of how tall the hat is overall. Most patterns give this as a fixed measurement for one size and it silently stops being right for any other.
Do bigger hats decrease faster?
No — and this is the genuinely surprising part. The decrease rate is 2π·h/w, the circumference having cancelled out of the arithmetic entirely. A 16-inch baby hat and a 24-inch adult hat lose the same number of stitches per round at the same gauge. The big hat just spends more rounds doing it.
How many stitches should I cast on?
The reduced circumference times your stitch gauge — but then adjust it to a number with useful divisors. This is the step that matters more than the quarter inch it costs, because a section count that does not divide the brim exactly cannot be worked.
Why is 100 stitches a bad number for a hat?
Because in the usable range it divides only by 4, 5 and 10. There is no 6-section and no 8-section crown available on 100 stitches, and those are the two most common. 96 and 120 both take 4, 6, 8 and 12. At four and a half stitches to the inch, moving from 100 to 96 costs under nine tenths of an inch of brim and buys the entire crown.
How much negative ease should a hat have?
Around two inches for a ribbed brim, which is what stops it riding up off the head. A non-stretchy fabric wants less because it cannot recover the difference, and a deep wide rib can take more. The ease is doing structural work, not styling.
Should I decrease every round or every other round?
Whichever your gauge and section count require — that is a consequence, not a choice. Divide the section count by the required rate and you get the rounds per decrease round. Advice copied from another pattern travels badly because it was derived from that pattern's gauge.
Why not decrease all the way to nothing?
Because it leaves a point on the top of the hat. Stop when there are few enough stitches to gather, cut the yarn, thread it through the live stitches and pull. The last small circle closes better as a gather than as more decrease rounds.
Does this work for a slouchy hat or a beret?
Not as-is. Those are deliberately not flat-topped crowns — a beret increases well past head circumference and then decreases back, so its crown is a much bigger disc than the head implies. The plan here closes the hat as a flat disc, which is what a standard beanie wants.
Where should I measure gauge for a hat?
Over the body stitch, not the brim. Ribbing measures dramatically smaller relaxed than it does on a head, so gauge taken over the brim will have you casting on far too many stitches. Work a plain section, measure that, and let the ease handle the brim.
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