How much yarn for a sweater

The honest answer is that it depends on your size, your gauge and how long you want the sleeves. But you do not have to guess. A swatch and five minutes of arithmetic get you close enough to buy with confidence.

Start with the pattern, if you have one

Patterns state yarn quantity per size, usually as a number of balls of a named yarn plus the metres per ball. If you are substituting a different yarn, ignore the ball count and use the metres. Ball weight and length vary between brands; metres do not.

If you have no pattern: the swatch method

This works for any garment, not only sweaters.

Knit a swatch at least 15 x 15 cm in the stitch pattern you plan to use. Wash and dry it the way you will wash the finished garment.
Measure the dry swatch and note its area in square centimetres.
Unravel the swatch and measure the yarn it used, in metres.
Divide metres by area. That gives metres per square centimetre.
Estimate the garment area as flat rectangles: front, back, two sleeves. Multiply width by length for each and add them up.
Multiply the garment area by your metres per square centimetre, then add 15% for ribbing, shaping, seams and a margin for error.

A worked example

A 15 x 15 cm swatch is 225 cm². If it used 30 m of yarn, that is 0.133 m per cm². Take a plain adult sweater with a body 55 cm wide and 65 cm long, front and back, and two sleeves of 40 x 50 cm:

Front: 55 x 65 = 3575 cm²
Back: 55 x 65 = 3575 cm²
Sleeves: 2 x (40 x 50) = 4000 cm²
Total: 11150 cm²

11150 x 0.133 is about 1487 m. Add 15% and buy for roughly 1700 m. If the yarn gives 105 m per 50 g ball, that is 17 balls.

Reading meterage on a product page

Where the supplier provides it, each yarn shows its ball weight and metres per ball, for example 105 m per 50 g. That is the number to divide into your total. Two yarns can both come in 50 g balls and still differ by 60 m per ball, which is three or four extra balls across a sweater.

Heavier yarn, fewer metres

A thicker yarn covers more area per metre than a fine one, so the same sweater takes fewer metres in a chunky yarn and more in a fingering yarn. The swatch method handles that automatically, which is why it beats any general table.

Buy the dye lot in one go

Yarn is dyed in batches, and two batches of the same shade can differ enough to show as a line across the chest. Buy all of it at once, and buy the spare ball now rather than later. Leftovers are useful; a mismatched sleeve is not.

Where to start

Sweater yarn, or browse by yarn weight and fibre.