Why are there different needle sizing systems?

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.

What size needles should I use for DK yarn?

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.

Are interchangeable needle tips the same sizes across brands?

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.

KnitCalcs

Needle Size Calculator — Metric, US & Old UK Conversion

Convert between metric (mm), US, and old UK knitting needle size systems.

Metric Size (mm)Select needle size in millimetres

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

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Row Gauge Calculator

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Stitch Gauge Calculator

Calculate how many stitches you need for a given width based on your stitch gauge.

Pattern Gauge Adjuster

Adjust pattern stitch counts when your gauge differs from the pattern gauge.

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.