Old knitting needle sizes: UK, US and metric conversion chart

You've found a lovely 1950s pattern and it asks for "a pair each of No. 12 and No. 10 needles". Your needles say 2.75 mm and 3.25 mm. Same thing? As it happens, yes.

Here's the one fact to hold on to: old British needle numbers go down as needles get thicker. A No. 14 is a skinny 2 mm needle; a No. 000 is a thick 10 mm one. Modern US sizes do the opposite, with small numbers for thin needles and big numbers for thick ones. So before you look anything up, work out which system your pattern uses. There's help with that further down.

The chart

These are the equivalents used by today's needle makers and yarn shops. Where a cell says "none", there isn't a matching size in that system. Pick the nearest size either side and knit a gauge (tension) swatch.

Three things the chart can't tell you:

• US 1½ and 2½ aren't official sizes. Different brands put them on different needles, so go by the millimetre figure.
• Needles vary. They can be a fraction of a millimetre off what's printed on them, old ones especially. If you have a needle gauge (the little card or metal plate with holes), use it.
• Canadian patterns from the same era generally used the British numbering, which is why modern charts put UK and Canadian sizes in one column. Australian and New Zealand patterns of the 1940s–60s also usually followed the British numbers.

UK or US? How to tell

It matters most at the extremes. Take three noughts:

• UK 000 = 10 mm. A thick needle for chunky yarn.
• US 000 = 1.5 mm. A fine needle for lace or socks.

Same printed size, and one needle is nearly seven times as thick as the other. These clues will sort it out.

Where was it printed? British, Irish, Canadian, Australian and New Zealand patterns from before the metric changeover almost always used the old UK numbers. American patterns used US numbers.

What yarn does it ask for? If the pattern wants 3-ply or 4-ply with No. 10 and No. 12 needles, that only makes sense as UK sizes (3.25 mm and 2.75 mm). A US 10 is 6 mm, far too thick for fine yarn, and there's no standard US 12 at all.

Which way round is the pairing? Ribbing is usually knitted on smaller needles than the body. In UK numbering the rib needle has the higher number ("No. 12 for the welt, No. 10 for the body"). In US numbering it has the lower number ("size 3 for the ribbing, size 5 for the body").

Is it an old American pattern for fine work? Some used a separate steel-needle scale where, as in the British system, higher numbers meant finer needles. A US pattern asking for "size 13" with fingering (4-ply) yarn is probably using that older steel scale (where 13 was about 2 mm), not modern US 13 (9 mm).

What does the gauge line say? If the pattern gives stitches per inch, that's your best clue of all. Eight stitches to the inch is fine yarn on fine needles, whatever the numbering says.

Reading a real needle line

Say your pattern says:

3 ozs. 3-ply. A pair each Nos. 10 and 12 needles. Tension: 8 sts. to 1 inch.

1. It's British (3-ply, ounces, "Nos."), so these are old UK sizes.
2. No. 12 = 2.75 mm (US 2) for the rib. No. 10 = 3.25 mm (US 3) for the body.
3. Eight stitches to the inch is about 31–32 stitches to 10 cm. That's the gauge you need to match, not just the needle size.
4. Cast on a swatch with 3.25 mm needles. If you get more stitches than 8 per inch, go up to 3.5 mm; if fewer, try 3 mm. Change the rib needle by the same step.

What 1940s and 1950s patterns usually called for

Mid-century British women's knitwear was mostly knitted in fine yarns: 2-ply, 3-ply and 4-ply. So you'll spend most of your time at the thin end of the chart.

A very common combination for a 3-ply or 4-ply sweater or cardigan was:

• No. 12 (2.75 mm) or No. 13 (2.25 mm) for welts, cuffs and bands;
• No. 10 (3.25 mm) or No. 11 (3 mm) for the main body.

Heavier garments, outdoor wear and accessories more often used sizes from No. 9 down to No. 5 (3.75 mm to 5.5 mm). By the 1970s, DK (light worsted) and chunkier yarns were much more common, and patterns from that decade start showing metric sizes, sometimes alongside the old numbers.

If a pattern seems to ask for oddly small needles for a whole adult garment, it probably isn't a mistake. Vintage gauges were often tighter than modern ball bands suggest, and that close, firm fabric is part of the look.

Why the numbers run backwards

Blame the wire. Steel knitting pins were made from drawn wire, and wire gets thinner by being pulled through a series of ever-smaller holes. The more times it's drawn, the higher the number and the finer the wire. Knitting needles borrowed those wire-gauge numbers, and from the 1880s the British Standard Wire Gauge (SWG) fixed exactly what each number meant. Earlier Victorian needle gauges didn't always agree with one another, so very old patterns can be less predictable still.

That explains a detail most charts skip. The SWG diameters don't land exactly on today's tidy metric sizes:

When Britain moved to metric needles in the 1970s, each old number was matched to the nearest sensible metric size. The differences are small, but they're one more reason a vintage knitter's No. 12 gauge and yours may not match perfectly, even if you both did everything "right". We don't know precisely how closely every maker of the time followed the wire gauge, so treat this table as background, not gospel.

The needle is only a starting point

A chart tells you which needle the original knitter probably used. It can't tell you what gauge you will get. Your yarn isn't theirs, your hands aren't theirs, and even the needle material (bamboo, metal, plastic) changes things.

The gauge is the real instruction. Knit a square at least 6 in (15 cm) across in the main stitch, wash and dry it the way you'll treat the finished garment, then measure the middle 4 in (10 cm). If it doesn't match, change needle size and try again. Our guide to measuring tension walks through it step by step.

If you'd rather skip the converting, our patterns are rebuilt from the original written instructions for your size, yarn and gauge, from US 4–24 / UK 8–28 (32–52 in bust). A knitter chose and checked every one, and if a needle size still puzzles you, email support@vintagetomodernknits.com and a real person will reply.

Also useful

• Old needle size converter tool
• How to measure tension (gauge) properly
• Vintage knitting abbreviations explained
• What is 3-ply yarn? Modern equivalents

Last updated 2026-10-11.