Amigurumi sphere calculator

How to use it

• Work a small swatch in single crochet with the yarn and hook you will use for the ball, as tightly as you would for a stuffed toy. Count the stitches across and the rounds up over 4 in (10 cm).
• Enter the diameter you want the stuffed ball to have, and your gauge. The pattern comes out round by round in single crochet (sc), US terms. In UK terms sc is double crochet.
• inc is two sc in the same stitch, and dec is sc2tog (two sc worked together). Each repeat is worked 6 times around the round.

How it works

A ball is a circle that grows, stops growing at the middle, then shrinks in the same way. The way around the middle is π (about 3.14) times the diameter, and your gauge turns that into stitches. A ball made this way starts with 6 stitches and gains 6 on every increase round, so the count has to be a multiple of 6 and the calculator gives you the nearest one.

Going over the top of a ball from one pole to the other is half the way around it. That sets the number of rounds, using how tall your rounds are compared with how wide your stitches are. The increase and decrease rounds use some of them, and the rest are even rounds worked at the full stitch count.

stitches around = π × diameter × stitches per unit, rounded to a multiple of 6
rounds in all = stitches around ÷ 2 × (rounds per unit ÷ stitches per unit)
even rounds = rounds in all − (stitches around ÷ 3 − 1)

Example: a 2 in ball at 24 stitches and 24 rounds in 4 in, which is 6 of each per inch. The way around a 2 in ball is π × 2 = 6.28 in, and 6.28 × 6 = 37.7 stitches. The nearest multiple of 6 is 36, which makes a ball 36 ÷ 6 ÷ π = 1.9 in across (42 stitches would make 2.2 in). Rounds in all: 36 ÷ 2 × 1 = 18. Increasing from 6 to 36 stitches takes 6 rounds and decreasing back to 6 takes 5 more, 11 in all, so 18 − 11 = 7 rounds are worked even. Round 1 is 6 sc in a magic ring, rounds 2 to 6 grow the ball to 36 stitches, rounds 7 to 13 are sc in each stitch ("sc around"), and rounds 14 to 18 shrink it back to 6.

On an increase round the changes are spread evenly: going from 30 stitches to 36 is (sc 4, inc) × 6, because 30 − 6 = 24 plain stitches shared between 6 increases is 4 each. Decrease rounds work the same way backwards, so 36 to 30 is (sc 4, dec) × 6. The crochet increase and decrease evenly calculator shows the same spacing for any other round.

Tips

• Stuffing stretches the stitches a little, so a firmly stuffed ball usually ends up a bit bigger than the calculation. Use a hook a size or two smaller than the yarn label suggests so the stuffing doesn't show through.
• Each extra set of 6 stitches makes the ball about 0.3 in (8 mm) wider at 6 stitches per inch. Thinner yarn and a smaller hook give finer steps.
• If the answer sits between two sizes, change the diameter a little until the count you prefer shows. The note under the result gives both counts.
• Stacking increases in the same place every round makes a hexagon instead of a circle. Start each increase round's repeats one or two stitches later than the round before.
• Mark the first stitch of each round with a stitch marker and count your stitches at the end of every round. It is much easier to fix a mistake one round later than ten.
• A ball that comes out squashed or oval means the even rounds don't fit your work. Measure the round gauge again on a stuffed piece, or add or remove an even round.