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US size 8 is 5.00 mm — the most common knitting needle in the world. This chart lists every US needle size from 0 to 50 with its metric size and the yarn weight each size suits, plus a live converter both ways: US size to millimetres, and millimetres to the nearest US size.
Knitting needles come in two numbering systems: US sizes, used in American patterns, and millimetres, used everywhere else. The two do not line up neatly — US 8 is 5.00 mm, US 10 is 6.00 mm, and the gaps between sizes grow as the needles get bigger. Enter a US size to get its metric size, or a millimetre size to find the nearest US size.
The chart below lists every standard US knitting needle size from 0 to 50 with its metric diameter in millimetres and the yarn weight each size is normally used with. US sizes are not evenly spaced: the small sizes step by 0.25 mm, the middle sizes by 0.50 mm, and the big sizes jump by whole millimetres and more. That is why a chart matters — you cannot work out US 15 from US 8 by adding a fixed amount. The highlighted row is US 8 at 5.00 mm, the anchor size most patterns are written around.
| US size | Metric (mm) | Yarn weight | Typical use |
|---|---|---|---|
| US 0 | 2.00 mm | Lace | Fine lace, cobweb and lace-weight yarns |
| US 1 | 2.25 mm | Fingering | Socks, fine shawls, lightweight lace |
| US 1.5 | 2.50 mm | Fingering | Lightweight socks and shawls |
| US 2 | 2.75 mm | Fingering | Socks, baby knits, fine garments |
| US 2.5 | 3.00 mm | Sport | Lightweight sweaters, baby clothes |
| US 3 | 3.25 mm | DK | Light garments, baby blankets |
| US 4 | 3.50 mm | DK | Sweaters, baby clothes, light scarves |
| US 5 | 3.75 mm | DK / Worsted | Light sweaters, hats, scarves |
| US 6 | 4.00 mm | Worsted | Sweaters, hats, mittens, blankets |
| US 7 | 4.50 mm | Worsted | Sweaters, scarves, afghans |
| US 8 | 5.00 mm | Worsted / Bulky | Sweaters, blankets, chunky hats |
| US 9 | 5.50 mm | Bulky | Chunky sweaters, scarves, blankets |
| US 10 | 6.00 mm | Bulky | Blankets, scarves, quick knits |
| US 10.5 | 6.50 mm | Bulky | Quick blankets, chunky cowls |
| US 11 | 8.00 mm | Super bulky | Chunky blankets, throws, rugs |
| US 13 | 9.00 mm | Super bulky | Throws, oversized scarves |
| US 15 | 10.00 mm | Super bulky | Arm-knit style blankets, throws |
| US 17 | 12.00 mm | Jumbo | Oversized blankets, giant throws |
| US 19 | 15.00 mm | Jumbo | Giant throws, statement blankets |
| US 35 | 19.00 mm | Jumbo | Extreme chunky knits, rugs |
| US 50 | 25.00 mm | Jumbo | Giant blankets, rugs, pet beds |
There is no formula to convert US needle sizes to millimetres — the US system is a numbering scheme, not a measurement, so the conversion is a published lookup table. The standard correspondence is the one used by needle makers and pattern publishers: US 0 is 2.00 mm, US 1 is 2.25 mm, US 2 is 2.75 mm, US 4 is 3.50 mm, US 6 is 4.00 mm, US 8 is 5.00 mm, US 10 is 6.00 mm, US 11 is 8.00 mm, US 15 is 10.00 mm, US 19 is 15.00 mm, and US 50 is 25.00 mm. The converter above looks up your size in that table; if you enter a size that is not in the table, it gives you the nearest standard size instead.
At the defaults — US size 8 and 5.00 mm — the lookup gives US 8 = 5.00 mm exactly, and the reverse lookup gives 5.00 mm = US 8 exactly. US 8 is the anchor of the whole chart: it is the size most worsted-weight sweater patterns are written for, and it is the size most knitters reach for first. The yarn weight for US 8 is worsted to bulky, and it is typically used for sweaters, blankets, and chunky hats.
US 0: the smallest standard size, 2.00 mm — used for lace and fingering yarns, fine lace shawls and cobweb-weight work. If your pattern calls for US 0 and your needles are metric, look for 2.00 mm.
US 6: 4.00 mm — worsted yarn, the workhorse size for sweaters, hats, and mittens. US 6 is one of the most common sizes after US 8, and it is the size many knitters learn on.
US 10: 6.00 mm — bulky yarn, blankets, scarves, and quick knits. The jump from US 8 (5.00 mm) to US 10 (6.00 mm) is a full millimetre, which is why a pattern written for US 10 knits up noticeably looser than one written for US 8.
US 15: 10.00 mm — super bulky yarn, arm-knit style blankets and throws. US 15 is where the chart stops being about garments and starts being about blankets: a 10.00 mm needle makes a fabric so open that only the bulkiest yarns hold together on it.
Reverse — 3.00 mm: the nearest US size to 3.00 mm is US 2.5, exactly 3.00 mm — sport-weight yarn, lightweight sweaters and baby clothes. A 3.00 mm needle is a common size in European patterns, and US 2.5 is the American size to reach for.
The correspondence in this chart is the standard published one used by needle manufacturers and pattern publishers in the United States and Europe. It is a lookup, not a calculation: the US numbers were assigned historically and do not follow a formula, so a size that is not in the table has no exact metric equivalent and the converter gives the nearest standard size instead. The yarn weights in the chart are the usual pairings, not rules — a pattern can call for any needle with any yarn, and the gauge (stitches per inch) is what actually matters: always knit a gauge swatch with the needles you have, because two 5.00 mm needles from different makers can knit slightly differently. Needle lengths, materials, and tip shapes do not change the size, and the chart covers straight, circular, and double-pointed needles alike. Rounding convention: millimetre sizes are shown to two decimal places, and all figures are exact table values, not computed approximations.
| Output | Formula | What it means |
|---|---|---|
| Metric size | table lookup: US → mm | 5.00 mm for US 8. |
| Yarn weight | table lookup: US → yarn | Worsted / Bulky for US 8. |
| Typical use | table lookup: US → use | Sweaters, blankets, chunky hats. |
| Nearest US size | table lookup: mm → nearest US | US 8 for 5.00 mm. |
| US 0 | table lookup | 2.00 mm — lace and fingering yarns. |
| US 6 | table lookup | 4.00 mm — worsted yarn, sweaters and hats. |
| US 10 | table lookup | 6.00 mm — bulky yarn, blankets and quick knits. |
| US 15 | table lookup | 10.00 mm — super bulky yarn, arm-knit style blankets. |
| Reverse: 3.00 mm | table lookup: mm → nearest US | US 2.5 — sport-weight yarn, lightweight sweaters. |
The US-to-mm correspondence in this chart is the standard published one, and every pairing on the page is an exact table value, not a calculation — US 8 is 5.00 mm by definition of the table, not by rounding. What the chart cannot do is guarantee your gauge: two needles marked 5.00 mm can knit differently if one is bamboo and the other is metal, and the yarn, your tension, and the pattern all move the finished size. It also cannot cover every maker’s odd sizes — some brands sell half sizes or sizes outside the standard table, and for those the converter gives the nearest standard size, which is a guide, not an exact match. The yarn weights are the usual pairings; a pattern can pair any yarn with any needle, and the gauge swatch is the final authority. For the yarn side of the same question, see the yarn weight chart; for what to knit with those needles, see the blanket size chart.
Bright Side Kit. "Knitting Needle Size Chart: US Sizes to mm Converter." https://brightoolbox.com/knitting-needle-size-chart/ Accessed October 24, 2026.5.00 mm. US 8 is the anchor size of the chart: 5.00 mm, used for worsted to bulky yarn, sweaters, blankets, and chunky hats. It is the size most American sweater patterns are written for.
Look it up — there is no formula. US sizes are a numbering scheme, not a measurement, so the conversion is a published table: US 0 is 2.00 mm, US 6 is 4.00 mm, US 8 is 5.00 mm, US 10 is 6.00 mm, and US 15 is 10.00 mm. Enter your size in the converter above for the exact value.
US 2.5. A 3.00 mm needle is exactly US 2.5 in the standard table, used for sport-weight yarn, lightweight sweaters, and baby clothes. If your European pattern says 3.00 mm, reach for US 2.5.
Usually US 7 to US 9 (4.50 to 5.50 mm). The most common is US 8 (5.00 mm). Check the ball band: it lists a recommended needle size, and the pattern’s gauge — stitches per inch — is the final check, not the size on the label.
No. US sizes run 0 to 50 and rise as the needle gets thicker; old UK sizes run the other way, with smaller numbers for thicker needles, and they do not line up with US sizes at all. Millimetres are the safe common language: a 5.00 mm needle is a 5.00 mm needle everywhere.
Because the US system is historical, not mathematical. The small sizes step by 0.25 mm, the middle sizes by 0.50 mm, and the big sizes jump by whole millimetres and more — US 11 is 8.00 mm, US 13 is 9.00 mm, US 15 is 10.00 mm. That is why a chart beats arithmetic.
US 50, which is 25.00 mm. It is a jumbo needle for giant blankets, rugs, and pet beds, used with the bulkiest yarns. Most knitters never go past US 15 (10.00 mm); the sizes above that are for statement pieces and arm knitting.
No, but it changes the gauge. A 5.00 mm bamboo needle and a 5.00 mm metal needle are the same diameter, but yarn slides faster on metal, so the same knitter often knits looser on metal. Always knit a gauge swatch with the actual needles you will use, whatever the chart says.