Crochet circles, balls and tubes, round by round

How to work it out yourself

Example: a round amigurumi ball in single crochet, starting with 6 sc in a magic ring and 6 increase rounds.

1. Round 1 is 6 stitches in the ring. Every round after it adds 6 more, so round r has 6 × r stitches. The edge grows as fast as the radius, which is why the circle lies flat.
2. In increase round r there are r − 2 stitches between the increases (2 sc in next st): round 3 is *1 sc, increase* six times, round 4 has 2 between them, and so on up to 36 stitches in round 6.
3. On the even rounds the increases move half a gap back, so they fall between those of the round before. Without it they stack into six corners and the ball turns into a hexagon.
4. Then 7 plain rounds, 6 + 1, on 36 stitches (rounds 7–13), and the decreases mirror the increases back down to 6, here with the invisible decrease (invdec). Stuff the ball before round 17.
5. Stitches in all: 126 + 252 + 90 = 468, over 18 rounds. That is the number the yarn amount calculator builds on.

Rnd 1: 6 sc in magic ring (6 sts) Rnd 2: 2 sc in each st (12 sts) Rnd 3: *1 sc, 2 sc in next st*, repeat from * to * 6 times in total (18 sts) Rnd 4: 1 sc, 2 sc in next st, *2 sc, 2 sc in next st*, repeat from * to * 5 times in total, 1 sc (24 sts) Rnd 5: *3 sc, 2 sc in next st*, repeat from * to * 6 times in total (30 sts) Rnd 6: 2 sc, 2 sc in next st, *4 sc, 2 sc in next st*, repeat from * to * 5 times in total, 2 sc (36 sts) Rnd 7–13: 1 sc in each st (36 sts) Rnd 14: 2 sc, invdec, *4 sc, invdec*, repeat from * to * 5 times in total, 2 sc (30 sts) Rnd 15: *3 sc, invdec*, repeat from * to * 6 times in total (24 sts) Rnd 16: 1 sc, invdec, *2 sc, invdec*, repeat from * to * 5 times in total, 1 sc (18 sts) Stuff the ball before the hole gets too small. Rnd 17: *1 sc, invdec*, repeat from * to * 6 times in total (12 sts) Rnd 18: invdec all around (6 sts) Cut the yarn, pull it through the front loops of the last 6 sts and pull tight.

A flat circle stops after the increase rounds; a tube carries on with plain rounds on the largest round. Taller stitches start with more in the ring: 8 half double or 12 double crochet.

Questions

Why 6 stitches in the magic ring?

Single crochet is about as tall as it is wide, and a circle of 6 sc that grows by 6 every round lies flat. Taller stitches need more to stay flat: 8 half double or 12 double crochet. You can enter anything from 3 to 16.

Why are some rounds moved half a gap?

If every increase sat right above the one before, they would stack into six corners and your circle or ball would turn hexagonal. Moving them half a gap on the even rounds keeps it round. Turn it off for clear lines, as at the top of a hat.

How many plain rounds does a ball need?

The calculator suggests one more than the increase rounds, which is closest to a true sphere. Fewer make a flatter ball, more a longer one; your stuffing and gauge matter as much.

Can I start from the size I want?

Yes. Choose Diameter and enter the size in cm and your stitches per 10 cm. The calculator finds the nearest number of increase rounds and says how big that comes out, before stuffing.