Knitting Needle Conversion Calculator

Two scales running opposite ways

The UK needle scale descends from wire gauge, where a larger number meant thinner wire, so UK sizes get smaller as the needle gets bigger. The US scale was numbered the intuitive way round, so US sizes get larger.

The consequence is that the two run in opposite directions and cross over in the middle of the common range. A US 8 is a UK 6; a US 6 is a UK 8. That symmetry is a coincidence of where the scales happen to sit, not a rule, and relying on it fails at both ends.

Metric is the only unambiguous scale, which is why modern patterns increasingly give millimetres alone and why it is the sensible thing to record when you find a needle that gives you gauge.

A worked example

A pattern from a British magazine calls for 5 mm needles and gives the size as a UK 6. In the US that is a size 8. A knitter reading the UK number as a US number would reach for 3.75 mm needles — a full 1.25 mm too small, which is two or three stitches per inch of difference and a garment several sizes out.

The reverse error is just as easy: a US 10 read as a UK 10 takes a 6 mm needle down to 3.25 mm.

Where the answer misleads

The scales are not complete mirrors of each other. Some metric sizes exist in one and not the other: 3 mm and 7 mm have UK numbers but no standard US equivalent, and 3.5 mm is a US 4 with no UK number. Translated patterns sometimes round to the nearest available size without saying so.

Manufacturers also vary slightly within a nominal size, particularly at the larger end and in wood or bamboo, where a 6.5 mm needle from one brand can measure 6.3 from another. If a swatch is stubbornly off gauge with the right nominal size, measure the needle itself with a gauge.

Finally, needle material changes gauge more than most knitters expect — commonly a quarter to a half stitch per inch between slick metal and grippy bamboo. The conversion gets you the right diameter, not the right fabric.