METRICATION:  90% complete
Metric Non-metric
Knitting yarn pack sizes in grams
Knitting and crochet needle diameters in millimetres
Knitting needle lengths in centimetres

Knitting yarn

In 1969, metric pack sizes were introduced for knitting yarns. Pack sizes of 20 g, 25 g, 40 g and 50 g were sold alongside the old ¾ oz (21 g) and 1 oz (28 g) packs. Imperial pack sizes were subsequently phased out.

New knitting patterns took account of the metric pack sizes when describing the number of balls of wool that they needed. At that time, knitting patterns also began to include body measurements in centimetres as well as inches.

Conversion tables were published to help work out the number of balls of wool needed for old knitting patterns.

Following the introduction of metric sizes, the 50 gram pack size soon became the new “standard” size for balls of wool, replacing the smaller, old 1 oz (28 g) size.

In 1976, BS 984, the British Standard for the determination of net mass of retail packages of knitting and rug yarns, was updated entirely in metric units.

In 1988, legislation was introduced to provide that knitting yarns should be pre-packed only in the following prescribed range of metric sizes:

10 g, 25 g, 50 g, 100 g, 150 g, 200 g, 250 g, 300 g, 350 g, 400 g, 450 g, 500 g, 1000 g

This legislation was subsequently revoked in 2014.

Knitting needles

Knitting needles are made with a range of different diameters, with thicker needles being used for coarser stitching. Prior to metrication, the diameters of knitting needles were described using a confusing system of size numbers, with larger numbers denoting smaller diameters. For example, a size 14 needle had a diameter of about 2 mm and a size 0 needle had a diameter of about 8 mm. For needles thicker than size 0, extra zeroes were used, with a size 000 needle corresponding to a diameter of 10 mm.

The old needle size numbers closely followed the non-linear, and now defunct, British Standard Wire Gauge (SWG) system for describing the thicknesses of wire.

In 1975, when fabrics for dressmaking began to be sold in metric lengths, and with knitting yarns already being sold in round metric pack sizes, the time had finally come to adopt metric units for a simpler, more intuitive method of labelling knitting needles.

In 1976, new knitting needles went on sale labelled with their diameters in millimetres, rather than with seemingly arbitrary size numbers. For a short transition period, packs with the new metric needles had dual size labelling while the sale of knitting needles using the old size numbers was phased out. By 1977, knitting needles were sold in packs with metric-only size labelling. Needle length descriptions also switched to centimetres at this time.

To avoid confusion with the old size numbers, the needle diameter labels on all metric knitting needles include the mm symbol.

Woolworth Knitting Magazine, Issue 7 – 1976

In order for old knitting patterns to remain usable with the new metric needles, a decision was taken for there to be a like-for-like metric replacement for each of the old needle sizes. Fortunately, a step size of 0.5 mm for the new needle size range corresponded almost exactly with most of the old size range. However, owing to the non-linear nature of the old size scale, additional fractional millimetre sizes were needed for needle sizes, in the range of 2 mm to 4 mm.

UK metric Old UK size Europe US size
2 mm 14 2 0
2.25 mm 13 2.5 1
2.75 mm 12 2
3 mm 11 3
3.25 mm 10 3.5 3
3.75 mm 9 5
4 mm 8 4 6
4.5 mm 7 4.5 7
5 mm 6 5 8
5.5 mm 5 5.5 9
6 mm 4 6 10
6.5 mm 3 6.5 10½
7 mm 2 7
7.5 mm 1 7.5
8 mm 0 8 11
9 mm 00 9 13
10 mm 000 10 15