How the sweater maths works

The rules, in the order they run

1. Gauge. Stitches divided by the width you counted them over gives stitches per inch or centimetre; rows divided by the height gives rows per inch or centimetre. Nothing else about the yarn is used.
2. Body panels. Chest plus ease, halved, is the width of the front and of the back. Times the stitch gauge gives a stitch count, which goes to the nearest count that fits your stitch multiple. An exact half goes up.
3. Rows. Every length times the row gauge, to the nearest whole row, an exact half up. So every length is within half a row of what you asked for.
4. Sleeve top and armhole. Upper arm plus its ease gives the sleeve top count. The top edge is sewn to the front and the back, so the armhole on the body is half the finished sleeve top, in whole rows.
5. The drop and the sleeve length. A drop-shoulder body is wider than your shoulders, so it hangs past each shoulder point by half the difference. The sleeve is your arm length minus that drop.
6. The taper. Worked from the top down, a decrease row takes one stitch off each edge, so the cuff count differs from the top by an even number and still fits the multiple. The rows after row 1 are shared out equally between the decrease rows, and each decrease row sits in the middle of its share. So the decreases come at two spacings a row apart (every 5th or 6th row, say), mixed along the sleeve, with about half a share worked even at the top and at the cuff. The edge never strays more than one stitch from a straight line from the sleeve top to the cuff. If the sleeve is too short to narrow that far, the cuff is made wider and the page says so.
7. The neck. The whole neck edge aims at your head plus 5 cm and is never narrower than 30 percent of your head. The neck count has the same odd or even as the panel, so both shoulders are equal. Then the opening is checked against your shoulder width: it must leave at least 2 cm of your own shoulder each side, or the sweater would slide off and the pattern is not written. Under 4 cm each side, a shoulder seam under 4 cm, or an edge smaller than your head gets a plain warning. A square front neck narrows the opening by its depth, which is the change to try first. Small children's heads are large for their shoulders, so this construction rarely suits them.
8. Finished sizes. Every finished measurement on the page, the schematic and the print is worked back from the whole counts, so you see what you will get.
9. Yarn. The area of the four pieces over the area of your whole swatch, times the yarn your swatch used, plus 10 percent, rounded up to the next 10 yards or metres. It is an estimate.

Worked example

A chest of 96 cm with 20 cm of ease, body length 60 cm, shoulders 40 cm, arm length 58 cm, upper arm 30 cm with 6 cm ease, wrist 16 cm with 6 cm ease and head 56 cm, with a half double crochet swatch of 16 stitches and 12 rows to 10 cm. The turning chain does not count. Every line below is printed by the same code that makes your pattern.

The back starts with a chain of 95: 93 stitches plus the 2 chains skipped at the start of row 1, which do not count. Each sleeve starts with 60 chains.

What it is based on, and what it assumes

• Engine version 2. The pattern code on every print starts with this number.
• Only your own measurements. There are no size charts in it.
• Your blocked swatch is trusted exactly. Fabric that grows with weight or washing will grow the sweater.
• Every piece starts from a foundation chain and is worked flat in rows.
• Widths are edge to edge on each piece; seams take up a little of each edge.
• Rounding: stitch counts to the nearest count that fits the multiple, rows to the nearest whole row, an exact half up. Sizes are shown to the nearest 0.1.
• Inches convert at exactly 2.54 cm and yards at exactly 0.9144 m. The same body in either unit gives the same counts.

Crochet terms are used descriptively. Yokewright is not affiliated with any yarn company, pattern publisher, crochet guild or standards body.