Everything in crochet that is not a rectangle is made with increases and decreases. Hats, toys, garments, circles, triangles, anything shaped — all of it is adding stitches in some places and removing them in others.

The good news is that there are only two ideas here, and they work the same way for every stitch height.

Increasing

An increase is two stitches worked into the same place.

That is the whole technique. Where you would normally work one stitch, work two. The extra stitch has to go somewhere, so the fabric gets wider.

Work your stitch as normal into the next stitch.
Work a second identical stitch into that same stitch.

You now have two stitches where the row below has one. Your count has gone up by one.

This works identically for single, half double, double, and treble crochet. Patterns write it as 2 sc in next st, 2 dc in next st, and so on. Occasionally you will see inc, which means the same thing.

For a bigger jump, work three or more into one stitch — 3 dc in next st adds two stitches. Shells and fans are exactly this, used decoratively instead of for shaping.

Decreasing

A decrease joins two stitches into one, by leaving the last loop of each on the hook and then closing them together.

Patterns write it as sc2tog, hdc2tog, dc2tog — read as “single crochet two together.” The number tells you how many stitches get absorbed, so dc3tog turns three stitches into one.

Single crochet decrease (`sc2tog`)

Insert the hook into the next stitch, yarn over, pull up a loop. Two loops on the hook.
Insert the hook into the following stitch, yarn over, pull up a loop. Three loops on the hook.
Yarn over and pull through all three loops.

One stitch where there were two.

Half double crochet decrease (`hdc2tog`)

Yarn over, insert the hook into the next stitch, yarn over, pull up a loop. Three loops.
Yarn over, insert the hook into the following stitch, yarn over, pull up a loop. Five loops.
Yarn over and pull through all five loops.

Double crochet decrease (`dc2tog`)

Yarn over, insert the hook into the next stitch, yarn over, pull up a loop, yarn over and pull through two loops. Two loops remain.
Yarn over, insert the hook into the following stitch, yarn over, pull up a loop, yarn over and pull through two loops. Three loops remain.
Yarn over and pull through all three loops.

Notice the pattern: you work each stitch normally but stop one step short, leaving it unfinished on the hook. Then you finish them all at once. That is the general rule for any decrease at any height, including trebles and clusters.

The invisible decrease, for amigurumi

The standard sc2tog leaves a small visible bump. On a stuffed toy, where every decrease sits on a curved surface in plain sight, that adds up. The invisible decrease is the fix, and it is worth learning if you make toys.

Insert the hook under the front loop only of the next stitch.
Insert the hook under the front loop only of the following stitch. Two front loops on the hook, plus your working loop.
Yarn over and pull through both front loops.
Yarn over and pull through the two loops remaining on the hook.

The result sits flatter and blends into the surrounding fabric. Same stitch count as a normal decrease, noticeably tidier surface.

Where to place them

This is what separates shaping that looks intentional from shaping that looks like a mistake.

At the edges, for garment shaping. Do not decrease into the very first or very last stitch of a row. It makes a ragged, stepped edge that is hard to seam. Work one stitch normally first, then decrease — so the shaping sits one stitch in from the edge, and the edge itself stays a clean straight column. Patterns usually specify this, and it is why they say things like sc in first st, sc2tog.

Spread evenly, for circles and crowns. When a pattern says to increase six times evenly around a round, it means to space them out — not to bunch them. Bunching creates corners; even spacing creates a curve. Most patterns tell you the exact placement, like [sc in next 3 sts, 2 sc in next st] 6 times.

Stacked, for a deliberate line. Working an increase or decrease in the same position every row creates a visible diagonal or a fold. That is how you get the pointed panels on a beret or the shaping line on a raglan sleeve.

Count at the end of every shaped row. Patterns give you a stitch count in parentheses precisely so you can catch an error immediately. On a shaped piece an uncaught mistake compounds — one lost stitch in a hat crown throws off every round after it.

Keeping a flat circle flat

Circles are pure increase math, and getting it wrong is the most common shaping problem beginners hit.

A flat circle in single crochet adds the same number of stitches every round as the first round contained. Start with 6, and every subsequent round adds 6: 6, then 12, then 18, then 24, then 30.

Taller stitches need more, because they cover more distance. A double crochet circle typically starts at 12 and adds 12 each round.

Two symptoms tell you what went wrong:

The circle cups upward like a bowl — too few increases. This is exactly what you want for a hat or a toy, and it is how you deliberately turn a circle into a dome: stop increasing and the fabric starts going up the sides instead of outward.
The circle ruffles and waves at the edge — too many increases. There is more fabric than the circumference needs.

Frequently asked

Is sc2tog the same as dec? Effectively yes. dec is the older, vaguer abbreviation; sc2tog and dc2tog say precisely which stitch and how many.

Can I increase and decrease in the same row? Yes, constantly. That is how darts, waists, and curved edges are made — add on one side, remove on the other, and the total width stays the same while the shape moves.

My decreases leave holes. Usually tension. Pull the final yarn-over slightly firmer when closing the loops. If it is amigurumi, switch to the invisible decrease.

Why does my hat come out flat instead of dome-shaped? You kept increasing too long. Once the flat circle reaches the diameter of the crown, stop increasing and work even rounds — that is what turns it into a dome and then a tube.

Do increases and decreases work the same in rows and rounds? Yes, mechanically identical. The only difference is placement: in rows they usually sit near the edges, in rounds they are spread around the circumference.