US 5 Knitting Needle: Metric & UK Size
US 5 is 3.75mm on a metric ruler, and UK/Canada (old) size 9 on an old chart. It sits at the boundary between sport weight's recommended range (US 3-5) and DK weight's (US 5-7), a genuinely common crossover point.
What it's typically used for
A firmer-than-standard DK fabric, or a looser-than-standard sport fabric — whichever direction you're approaching it from. It's also a popular choice for ribbed cuffs and brims on a DK-weight project, where a smaller needle than the body produces a snugger, more elastic edge, following the same logic covered on the 1x1 rib page.
Its place in the wider table
US 4 (3.5mm) has no UK old number at all; US 6 (4.0mm) is UK 8. Moving from US 4 through US 5 to US 6, the UK count resumes its normal downward march (none, then 9, then 8) — the missing number at US 4 is a one-off gap, not a sign the whole system is irregular through this stretch.
Gauge implications
Because US 5 straddles two weight categories, which direction you'll want to size from depends on your yarn: coming from sport weight, expect denser and firmer than sport's standard range predicts; coming from DK weight, expect looser and more open than DK's standard range predicts. Swatch and compare against whichever weight's specific published gauge range actually applies to your yarn.
FAQ
Is US 5 a common size for ribbed hat brims specifically? Yes — many hat patterns call for a needle one or two sizes smaller than the body for the brim specifically, and if the body is worked at a standard DK needle size (US 6-7), US 5 is a common brim choice for extra snugness.
What's the UK 9 equivalent used for historically? UK 9 (3.75mm) needles appear regularly in vintage British patterns for lightweight garments and baby knits, corresponding to what would now be labeled sport-to-DK weight territory.
Does US 5 come in interchangeable needle tip sets? Yes — it's a common size in most interchangeable circular needle systems, given how frequently it's called for across sport and DK-weight patterns.