KnitCalcs
Needle Size Calculator — Metric, US & Old UK Conversion
Convert between metric (mm), US, and old UK knitting needle size systems.
How We Calculate This
This converter uses the standard international needle size equivalency table. Select a metric size to see the equivalent US and old UK sizes.
Advanced Options let you check whether the selected needle is appropriate for your yarn weight and apply a material stiffness adjustment — stiffer fibres like linen and cotton typically benefit from going up a needle size.
Key conversions
- 2mm = US 0 = Old UK 14
- 4mm = US 6 = Old UK 8
- 5mm = US 8 = Old UK 6
- 6mm = US 10 = Old UK 4
- 8mm = US 11 = Old UK 0
Frequently Asked Questions
Different countries developed their own numbering systems before metric standardisation. The US system uses increasing numbers for larger needles. The old UK system uses decreasing numbers (14 is smallest, 000 is largest). Metric (mm) is now the international standard and is the most precise way to specify needle size.
DK (Double Knitting) yarn typically uses 3.75-4.5mm needles (US 5-7). Start with 4mm (US 6) and adjust based on your swatch gauge. If your tension is tight, go up; if loose, go down.
Metric sizes are standardised, but some brands run very slightly larger or smaller. This rarely matters unless you are mixing tips and cables from different brands. Always use the same brand within a project for consistency.
Related Calculators
International Gauge Calculator
Convert gauge measurements between metric and imperial systems.
Gauge Conversion Calculator
Convert gauge between 10cm and 4-inch standards.
Gauge Swatch Calculator
Calculate stitches and rows per cm from your swatch measurements.
Row Gauge Calculator
Calculate how many rows you need for a given length based on your row gauge.
Stitch Gauge Calculator
Calculate how many stitches you need for a given width based on your stitch gauge.
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Last updated: February 2026
All calculations are estimates based on standard yarn weights and gauge. Results may vary with individual tension, yarn brand, and needle size.