# Knitting Needle Converter

> Knitting needle converter: US, mm and UK needle sizes. Free knitting needle converter with the formula shown - runs entirely in your browser, no signup.

- **Canonical URL:** https://boringtoolskit.com/knitting-needle-converter/
- **Category:** Converters
- **Evidence level:** authored-methodology
- **Reviewed:** 2026-09-20
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

US needle sizes have no formula — they are a fixed mapping to mm (US 8 = 5.0 mm, US 10 = 6.0 mm, US 13 = 9.0 mm). UK old sizes run inverse (bigger number = thinner needle).

## Assumptions

- Manufacturer charts vary; conversion outputs are the standard-mapping midpoint.
- Measurements are body measurements unless the tool labels them as garment measurements.
- Between-size results round per the rule stated in the FAQ.

## Common questions

### My swatch is off gauge with the recommended needle. What now?

That is the system working: go up a needle size for too-many stitches per inch, down for too few. Gauge is the target; the printed needle size is only a starting suggestion.

## Sources

- [Aggregated manufacturer sizing conventions](https://boringtoolskit.com/methodology/)

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