Knitting Needle Size Converter

Convert knitting needle sizes between metric millimetres, US numbers and old UK numbers.

Knitting needle sizing is one of the few places where three numbering systems are still in everyday use, and a pattern written in one is easy to misread in another. This converter reads across metric, US and old UK sizes and shows the gauge each size normally produces.

At a glance

What you enter: Needle size (metric)
What you get: Size recognised, Suits chunky yarn and above, Suits fine yarn and below, Yarn weight class this suits
Formula shown: Yes, every step, right below your results.
Cost and privacy: Free, no account needed, and nothing you type is stored.

See worked examples ↓ Read the FAQ ↓ Share this calculator ↓

Needle size (metric)

Reset

Size recognised 1

Suits chunky yarn and above 0

Suits fine yarn and below 0

Yarn weight class this suits 1

How is this calculated?

The metric size is the fixed reference. US and old UK numbers are mapped to it from the standard needle conversion chart.

Several sizes have no exact equivalent in the older numbering systems, which is why the chart records a dash for those. The full table below lets you read across any size.

Typical gauge figures are for worsted weight yarn in stockinette. Ribbing, cables and colourwork all pull the gauge in, so swatch in the stitch you are actually working.

Knitting needle size chart

Metric	US	Old UK	Typical gauge (st per 4 in)
2 mm	0	14	33
2.25 mm	1	13	30
2.75 mm	2	12	28
3 mm	-	11	26
3.25 mm	3	10	25
3.5 mm	4	-	24
3.75 mm	5	9	23
4 mm	6	8	22
4.5 mm	7	7	20
5 mm	8	6	18
5.5 mm	9	5	17
6 mm	10	4	16
6.5 mm	10.5	3	15
7 mm	-	2	14
8 mm	11	0	12
9 mm	13	00	11
10 mm	15	000	10
12 mm	17	-	9
15 mm	19	-	8
16 mm	-	-	7
19 mm	35	-	6
25 mm	50	-	5

Your numbers stay in the address bar, the link reproduces this exact calculation.

Results are estimates for general information only, always verify with a professional or official source before acting on them.

How to use the Knitting Needle Size Converter

1 Enter Needle size (metric)
2 Press Calculate. You get Size recognised, Suits chunky yarn and above, Suits fine yarn and below, Yarn weight class this suits, and every intermediate step stays visible under "How is this calculated?"
3 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.

Worked examples

Real numbers run through this calculator. Open any example to load it into the form above and change it.

US 7 needles

A pattern written in US sizes and your needles are metric.

You enter

Needle size (metric): 4.5

You get

Size recognised: 1
Suits chunky yarn and above: 0
Suits fine yarn and below: 0
Yarn weight class this suits: 1

US 7 is 4.50 mm.

Open this example in the calculator →

Bulky sweater

A chunky pattern suggests US 11 needles.

You enter

Needle size (metric): 8

You get

Size recognised: 1
Suits chunky yarn and above: 1
Suits fine yarn and below: 0
Yarn weight class this suits: 2

US 11 is 8.00 mm.

Open this example in the calculator →

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Frequently asked questions

What is a US 7 knitting needle in millimetres?

A US 7 is 4.50 mm. That is the same as an old UK 7, but that is coincidence rather than a rule: for most sizes the two numbering systems differ, which is why this converter lists both.

Are circular and straight needles sized the same way?

Yes. The size refers to the shaft diameter, not the length or the tip style. A 4.00 mm circular and a 4.00 mm straight needle produce the same gauge in the same yarn and stitch.

Why does my gauge not match the typical figure?

Because typical figures describe an average hand with an average worsted yarn. Your tension, the fibre, the ply and the stitch pattern all move it. Match your swatch to the gauge the pattern asks for and let the needle size be whatever gets you there.

How do I convert a pattern from US to metric needles?

Look up each US number in a conversion chart, write the metric size against it, then shop in millimetres. Metric sizing is the most widely available internationally and is the number printed on most modern needle packaging.