Needle Size Converter
Convert between US, UK, and metric knitting needle sizes instantly.
| US | MM | UK |
|---|---|---|
| US 000 | 1.5 mm | UK label not verified — use 1.5 mm |
| US 00 | 1.75 mm | UK label not verified — use 1.75 mm |
| US 0 | 2 mm | UK 14 |
| US 1 | 2.25 mm | UK 13 |
| US 1.5 | 2.5 mm | UK label not verified — use 2.5 mm |
| US 2 | 2.75 mm | UK 12 |
| US 2.5 | 3 mm | UK 11 |
| US 3 | 3.25 mm | UK 10 |
| US 4 | 3.5 mm | UK label not verified — use 3.5 mm |
| US 5 | 3.75 mm | UK 9 |
| US 6 | 4 mm | UK 8 |
| US 7 | 4.5 mm | UK 7 |
| US 8 | 5 mm | UK 6 |
| US 9 | 5.5 mm | UK 5 |
| US 10 | 6 mm | UK 4 |
| US 10.5 | 6.5 mm | UK 3 |
| US 11 | 8 mm | UK 0 |
| US 13 | 9 mm | UK label not verified — use 9 mm |
| US 15 | 10 mm | UK label not verified — use 10 mm |
| US 17 | 12 mm | UK label not verified — use 12 mm |
| US 19 | 15 mm | UK label not verified — use 15 mm |
| US 35 | 19 mm | UK label not verified — use 19 mm |
| US 50 | 25 mm | UK label not verified — use 25 mm |
UK labels are shown only for verified mappings in this chart. An unverified label does not mean that no historical equivalent exists. Manufacturer conventions can differ; use the diameter marked in millimeters and check your pattern gauge. UK conversion reference: KnitPro.
How to Use the Needle Size Converter
Three simple steps to find your perfect needle size
Pick Your System
Select your known size from any of the three dropdowns — US, metric (mm), or UK/Canadian. The other two fields will update automatically.
Read Your Conversion
The other dropdowns update and the matching chart row is highlighted. If a UK label is not verified, use the displayed millimeter diameter instead.
Check Typical Uses
Use the yarn-weight guide below as a starting point, then follow your pattern and check your gauge with a swatch.
Understanding Needle Sizing Systems
Why do the US, UK, and metric systems use different numbers for the same needle?
The US System
US sizes use numbers rather than direct diameter measurements. Smaller numbers generally indicate thinner needles; very fine sizes include 0, 00 and 000. US labels appear in many North American knitting patterns. Check the millimeter marking when comparing brands or using an older pattern.
US numbers do not increase in equal millimeter steps. Common examples include US 10 at 6.0 mm, US 10.5 at 6.5 mm and US 11 at 8.0 mm. Some manufacturers also offer intermediate sizes, so compare the diameter rather than assuming a fixed step between labels.
The Metric System (mm)
Metric sizing states the diameter of the needle shaft in millimeters. A 4.0 mm marking specifies that diameter directly, without requiring a US or UK number conversion. Check the marked diameter on the needle or packaging when comparing sizes.
If your needle does not have its size printed on it, you can measure it precisely with a needle gauge tool — a small card or ruler with labeled holes of exact mm sizes.
The UK & Canadian System
Traditional UK and Canadian numbering generally works in reverse: higher numbers indicate thinner needles. For example, UK 8 corresponds to 4.0 mm and UK 4 to 6.0 mm in the referenced chart. Historical labels and manufacturer charts can vary, so this converter leaves uncertain UK labels unverified.
When working from an older British pattern, identify its sizing system and compare the intended millimeter diameter before buying replacement needles.
Why Sizes Don't Always Match
Manufacturer sizing conventions can differ, especially for intermediate and larger sizes. The millimeter measurement on the needle or packaging is the clearest reference. Even with the correct diameter, your yarn, stitch pattern and tension affect gauge, so knit a swatch before starting a fitted project.
When in doubt, the millimeter measurement is your most reliable reference point. Use a needle gauge to verify the actual size of any needle before you cast on.
Which Needle Size for Which Yarn Weight?
A quick-reference guide to matching needles and yarn
| Yarn Weight | US Size | Metric (mm) | Stockinette stitches per 4" | Example Projects |
|---|---|---|---|---|
| 0 · Lace | 000–1 | 1.5–2.25 | 33–40 | Shawls and lace scarves |
| 1 · Super Fine / Fingering | 1–3 | 2.25–3.25 | 27–32 | Socks and lightweight shawls |
| 2 · Fine / Sport | 3–5 | 3.25–3.75 | 23–26 | Lightweight garments |
| 3 · Light / DK | 5–7 | 3.75–4.5 | 21–24 | Sweaters and hats |
| 4 · Medium / Worsted / Aran | 7–9 | 4.5–5.5 | 16–20 | Scarves and garments |
| 5 · Bulky / Chunky | 9–11 | 5.5–8 | 12–15 | Thick sweaters and cowls |
| 6 · Super Bulky | 11–17 | 8–12.75 | 7–11 | Chunky blankets |
| 7 · Jumbo | 17 and larger | 12.75 and larger | 6 or fewer | Oversized blankets |
These are guidelines, not pattern requirements. Lace often uses larger needles for openwork. Follow your pattern and measured gauge. Source: Craft Yarn Council yarn-weight system.
Frequently Asked Questions
Common questions about needle sizes answered
What is the most common knitting needle size for beginners?
US size 7 or 8 (4.5–5.0 mm) is widely recommended for beginners. These mid-range sizes work well with DK or worsted weight yarn, which is forgiving and easy to handle. The stitches are large enough to see clearly without being so large that the work becomes floppy.
Can I use a different needle size than what the pattern recommends?
Yes — and you often should. Needle size recommendations on patterns are a starting point, not a rule. What matters is your gauge (how many stitches and rows fit in 4 inches / 10 cm). Knit a swatch, measure it, and go up or down a needle size until your gauge matches the pattern. Knitting tightly? Go up a size. Knitting loosely? Go down a size.
Why does the converter show an unverified UK label?
The converter includes UK labels only where the mapping has been verified. Some sizes are missing or inconsistent in reference charts. An unverified label does not prove that a historical equivalent never existed. Use the millimeter diameter and check the sizing information supplied with your pattern or needles.
Are bamboo and metal needles the same size?
A 5.0 mm bamboo needle and a 5.0 mm metal needle have the same stated diameter. Their surfaces feel different, and changing material can affect your tension. There is no automatic size adjustment that works for everyone: knit another swatch and change the diameter only if needed to match your pattern gauge.
What needle size do I need for sock knitting?
Many fingering-weight sock patterns use small needles, such as 2.25–2.75 mm (commonly US 1–2), to make a firm fabric. Other yarn weights and patterns need different sizes. Follow the pattern gauge and swatch first. Double-pointed needles, suitable circular needles or the magic-loop method can be used for knitting in the round.
How do I find out what size my unlabeled needles are?
Use a needle gauge — a flat tool with labeled holes in precise millimeter sizes. Slide the needle into holes until you find the smallest hole it fits through without forcing. That hole's label is your needle size. Needle gauges are inexpensive, widely available at craft stores, and an essential tool for any knitting kit. Avoid using a ruler to eyeball it — even a 0.25 mm difference matters for gauge.
What is the difference between US and UK size 4?
US size 4 commonly corresponds to 3.5 mm. UK size 4 corresponds to 6.0 mm, commonly US size 10, in the referenced conversion chart. The same number means different diameters in the two systems. Check the millimeter marking rather than matching the number alone.
What needle size is best for knitting a blanket?
Choose the size for your yarn, stitch pattern and desired fabric. A blanket pattern normally supplies a starting needle size and target gauge. Heavier yarns generally use larger needles, but the finished fabric also depends on your tension. Swatch, check the feel of the fabric and measure before calculating the blanket dimensions.
Pro Tips for Choosing Needle Sizes
Practical ways to choose a starting size and check your gauge
Always Swatch First
Knit at least a 6" x 6" swatch in your chosen stitch pattern before starting any sized project. Wash and block it exactly as you plan to treat the finished item, then measure. Gauge can change significantly after blocking, especially with natural fibers like wool and cotton.
Go Up for Drape, Down for Structure
Using a needle one or two sizes larger than recommended creates a looser, drapier fabric — great for shawls and flowy cardigans. Going down a size creates a denser, more structured fabric — ideal for bags, toys, or garments that need to hold their shape. Neither is wrong; it depends on your goal.
Your Tension Is Unique
A pattern gives the target gauge needed for its intended measurements. If your swatch has more stitches per inch than the target, try a larger needle. If it has fewer, try a smaller needle. Knit and measure another swatch after each adjustment.
Check the Yarn Label First
Yarn labels often suggest a needle size and gauge. These help you choose a starting point when designing your own project. When following a pattern, use its needle recommendation and target gauge, then adjust according to your swatch.
Use Different Sizes for Different Parts
Many patterns call for a smaller needle for the ribbing or cuffs (to make them snug and elastic) and a larger needle for the body. This is not a mistake in the pattern — it is intentional shaping technique. Keep both sizes on hand before you start.
Build a Core Needle Collection
Start with the needle sizes and lengths your chosen patterns need, then add others as your projects change. If considering an interchangeable set, check its diameter range, cable lengths and minimum circular length against the projects you plan to knit.
Recommended Needle Sizes for Popular Projects
Illustrative starting points — your pattern and measured gauge determine the size
Fingering / DK
DK / Sport
DK / Worsted
Fingering / Sport
Worsted
Fingering / Sock
Worsted / Aran
Lace / Fingering
Bulky / Chunky
Cotton / DK
Sport / DK
Cotton DK / Sport
Using Vintage Needle Sizes Safely
Before converting an older pattern, identify whether its needle numbers refer to US, UK or another sizing system. Check any explanatory notes, publisher information or diameter measurements in the pattern.
Compare the intended diameter with the millimeter marking on your needles. For an unlabeled needle, use a needle gauge. A matching US or UK number alone is not enough when charts or manufacturer conventions differ.
Treat an unverified conversion as a reason to check the original pattern or manufacturer chart. Do not substitute a guessed UK label. The millimeter diameter is the practical comparison between numbering systems.
Once you have selected a starting needle, knit a swatch in the specified stitch pattern and check it against the pattern gauge. Adjust the needle diameter as needed before beginning a fitted garment.
Ready to Calculate Your Gauge?
Now that you have the right needle size, use our Gauge Calculator to check your stitch count and make sure your project turns out exactly the right size.