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General product information only, not medical advice. Choosing a needle or catheter for a person or procedure is a decision for a trained clinician following the manufacturer’s instructions for use.
Gauge is a legacy size label: a higher number means a thinner needle. The only colour-code standard that covers the whole range, ISO 6009:2016, runs from 34 gauge (0.18 mm, the thinnest) to 10 gauge (3.4 mm, the widest). The two tables below put every gauge in that range next to its designated metric size and hub colour. For catheter-specific sizing see our IV catheter gauge selection guide; for the scale itself see why a bigger gauge is a smaller needle.
Needle gauge size chart (34G to 10G)
Values are copied from Table 1 of ISO 6009:2016, Hypodermic needles for single use: Colour coding for identification. The standard defines “designated metric size” as the outer diameter designation of the tubing, and “gauge” as a legacy size designation. A gauge corresponds to a designated metric size that defines limits for outer diameters.
Thin needles: 34G to 24G
| Gauge | Designated metric size (mm) | ISO 6009 hub colour |
|---|---|---|
| 34G | 0.18 | Orange |
| 33G | 0.2 | Black |
| 32G | 0.23 | Deep green |
| 31G | 0.25 | White |
| 30G | 0.3 | Yellow |
| 29G | 0.33 | Red |
| 28G | 0.36 | Blue-green |
| 27G | 0.4 | Medium grey |
| 26G | 0.45 | Brown |
| 25G | 0.5 | Orange |
| 24G | 0.55 | Medium purple |
Mid to wide needles: 23G to 10G
| Gauge | Designated metric size (mm) | ISO 6009 hub colour |
|---|---|---|
| 23G | 0.6 | Deep blue |
| 22G | 0.7 | Black |
| 21G | 0.8 | Deep green |
| 20G | 0.9 | Yellow |
| 19G | 1.1 | Cream |
| 18G | 1.2 | Pink |
| 17G | 1.4 | Red-violet |
| 16G | 1.6 | White |
| 15G | 1.8 | Blue-grey |
| 14G | 2.1 | Pale green |
| 13G | 2.4 | Purple |
| 12G | 2.7 | Pale blue |
| 11G | 3.0 | Green-yellow |
| 10G | 3.4 | Olive brown |
Check your product’s labelling. The standard’s own introduction says a colour code is for rapid visual identification and “does not absolve the user of the responsibility to check the marked size of the needle”. The standard also does not require needles to be colour-coded at all; product standards such as ISO 7864 may.
How to read the chart
- Higher gauge number, thinner needle. 34G is 0.18 mm; 10G is 3.4 mm.
- Millimetres are the designation. The metric size describes the outer diameter of the tubing; gauge is the older label for the same size.
- Colour is a shortcut. Use it to spot a size quickly, then confirm against the printed size on the hub or pack.
What is the largest needle gauge?
“Largest gauge” is ambiguous. By number, the largest gauge in ISO 6009 is 34G, which is the thinnest needle (0.18 mm). By diameter, the largest needle in the standard is 10G (3.4 mm), which has the smallest gauge number. When a supplier or colleague says “biggest gauge needle”, confirm whether they mean the number or the bore.
What is the smallest gauge needle?
By number, the smallest gauge in ISO 6009 is 10G, the widest needle at 3.4 mm. By diameter, the smallest needle in the standard is 34G at 0.18 mm. The same number-versus-bore ambiguity applies, so state both the gauge and the millimetre size.
Needle versus IV catheter sizes
ISO 6009 applies to single-use hypodermic needles. Do not assume its hub colours carry over to intravenous catheters; catheters are sold as a separate product type, and their colour conventions are set by their own product documentation. Our guides to the IV catheter and the butterfly needle cover those devices, and French to mm conversion covers catheters sized in French rather than gauge. A needle chart is not a flow-rate or suitability chart.
Common mix-ups
- Colour instead of the printed size. The standard says the colour does not replace checking the marked size.
- Needle colours applied to catheters. The ISO 6009 scope is single-use hypodermic needles.
- Pen needles. ISO 6009 is not applicable to pen-needles.
- 7, 9 and 0 gauge. These fall outside the standard’s 10G to 34G range, so the table has no row for them. Rely on the manufacturer’s labelling for any size outside that range.
What to check on the label
- The marked gauge and the millimetre size, and whether they agree with the hub colour.
- Whether the pack says single-use, as ISO 6009 covers single-use hypodermic needles.
- Which standard or instructions for use the manufacturer cites.
FAQ
What is the largest needle gauge?
34G by number (0.18 mm, thinnest); 10G by diameter (3.4 mm, widest), within the range ISO 6009 covers.
What is the smallest gauge needle?
10G by number (3.4 mm, widest); 34G by diameter (0.18 mm, thinnest), within the same range.
Are 7, 9 and 0 gauge needles in the standard?
No. ISO 6009 covers 0.18 mm (34G) to 3.4 mm (10G). Check the manufacturer’s labelling for other sizes.
Does the hub colour guarantee the size?
No. ISO 6009 states the colour does not absolve the user of checking the marked size.
Sources
- ISO 6009:2016, Hypodermic needles for single use: Colour coding for identification, 4th edition, 2016-08-01 (scope, definitions, introduction and Table 1; checked 2026-11-01). International Organization for Standardization, Preview of the standard: https://cdn.standards.iteh.ai/samples/63277/1a6f149bb0c8466f834702affa19c63b/ISO-6009-2016.pdf.
