US 8 Knitting Needle: Metric & UK Size
US 8 converts to 5.0mm, or UK/Canada (old) size 6 — right in the middle of worsted weight's standard recommended range (US 7-9), and arguably the single most reached-for needle size in general knitting.
What it's typically used for
Sweaters, hats, mittens, and blankets — the default choice across a huge share of worsted-weight patterns. If a pattern doesn't specify an unusual gauge and simply calls for "worsted weight, US 7-9," US 8 is the reasonable middle starting point most knitters swatch first before adjusting based on their own tension.
Its place in the wider table
US 7 sits one step down at 4.5mm (UK 7); US 9 sits one step up at 5.5mm (UK 5). Worsted weight's entire recommended range, US 7 through 9, maps to UK old 7 through 5 — a genuinely narrow, easy-to-remember band, which is part of why worsted-weight vintage British patterns are relatively easy to convert compared to some other weights.
Gauge implications
Worsted's standard published range (16-20 stitches per 4 inches) typically lands close to the middle of that band on a US 8 needle for most worsted yarns. Because it's such a commonly used size, it's also the size most worsted-weight yarn manufacturers test and print their own recommended gauge against on the ball band — see reading the gauge on a yarn label for how much to trust that printed recommendation versus your own swatch.
FAQ
Is US 8 a safe default needle size to buy first? It's a genuinely reasonable single-size starting point given how often worsted-weight patterns call for something in its neighborhood, though it shouldn't replace swatching and adjusting for your own specific project and tension.
What's the closest crochet hook to a US 8 knitting needle? An H-8 hook (5.0mm) matches exactly in diameter, coincidentally sharing the same "8" in its name — a coincidence specific to this one size, not a pattern that holds across the rest of the needle-and-hook naming systems.
Why is UK 6 sometimes printed as just "6" and sometimes with additional letters on vintage needles? Some manufacturers stamped needles with the UK number alone, others added additional letter codes for their own internal size systems — always cross-check a vintage needle's stamped number against a metric measurement if you're unsure, rather than trusting a stamp you can't otherwise verify.