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General product information only, not medical advice. This page does not say which needle to use with any heparin product or for any patient; follow the product labelling and your facility’s protocols.
Heparin is supplied and drawn up in many forms, and the needle that goes on the syringe is a separate product with its own size marking. This page is a lookup for that marking: it gives the gauge, the nominal outer diameter in millimetres and the hub colour that ISO 6009:2016 assigns to each size of single-use hypodermic needle. The standard defines the colour for a size; it does not tell you which size suits a given drug or task.
Needle gauge, millimetre and hub colour chart (ISO 6009:2016)
| Gauge (G) | Nominal outer diameter | ISO 6009 hub colour |
|---|---|---|
| 16G | 1.6 mm | White |
| 17G | 1.4 mm | Red-violet |
| 18G | 1.2 mm | Pink |
| 19G | 1.1 mm | Cream |
| 20G | 0.9 mm | Yellow |
| 21G | 0.8 mm | Deep green |
| 22G | 0.7 mm | Black |
| 23G | 0.6 mm | Deep blue |
| 24G | 0.55 mm | Medium purple |
| 25G | 0.5 mm | Orange |
| 26G | 0.45 mm | Brown |
| 27G | 0.4 mm | Medium grey |
| 28G | 0.36 mm | Blue-green |
| 29G | 0.33 mm | Red |
| 30G | 0.3 mm | Yellow |
Values are copied from Table 1 of ISO 6009:2016, Hypodermic needles for single use – Colour coding for identification (fourth edition, 2016-08-01). Checked 1 November 2026. The standard covers sizes from 0.18 mm (34G) to 3.4 mm (10G); this chart shows 16G to 30G. Check your product’s labelling: the size printed on the needle or its package is what counts.
How to read the chart
The metric figure is the nominal outer diameter of the needle tube, and it is the designation the standard uses. ISO 6009 describes gauge as a “legacy size designation”. A higher gauge number means a thinner needle: 30G is 0.3 mm, 18G is 1.2 mm. The colour is meant to indicate the nominal outer diameter.
The standard says that colour coding on a needle or package does not relieve the user of the responsibility to check the marked size. It also does not require needles to be colour-coded or say which part of the needle or packaging carries the colour; that is left to other product standards such as ISO 7864.
Gauge, millimetres and what the standard does not cover
Gauge and millimetres are two names for the same outer diameter, so the chart works in both directions: find the gauge printed on the pack and read across to the diameter, or start from a millimetre figure on a data sheet. Needle length is a separate dimension and is not in this chart. Length, wall thickness and tip type appear in the manufacturer’s description of the product.
ISO 6009 is not applicable to pen-needles. A pen-needle or insulin-pen needle is not covered by this colour code, so do not use the chart to identify one.
Check what the heparin product label says
Before assuming any needle fits a particular heparin product, read the labelling that came with that product and with the syringe or needle. Items worth confirming from the documents themselves:
- the gauge and length marked on the needle pack;
- the connector type on the syringe and needle (a needle hub is designed to mate with the syringe nozzle);
- whether the product is supplied as a syringe with a needle attached, or as a syringe intended to be used with a separate needle, as stated by its manufacturer;
- any needle size or device instruction given in the heparin product’s own instructions for use.
In the United States a hypodermic single lumen needle is defined in 21 CFR 880.5570 as a metal tube sharpened at one end and joined at the other to a female connector (hub) designed to mate with the male connector (nozzle) of a piston syringe or an intravascular administration set. The regulation classifies it as Class II (performance standards). Source: eCFR, checked 1 November 2026.
For heparin used to coat a syringe in blood gas sampling, see heparinized syringes: dry versus liquid heparin. For a related flush product, see what a saline flush is.
Common mix-ups
- Colours repeat. In the 16G to 30G range, ISO 6009 uses yellow for both 30G and 20G, and white for 16G and 31G. Across the whole standard, orange is 34G and 25G, black is 33G and 22G, and deep green is 32G and 21G. Confirm the number, not only the colour.
- Gauge is not length. A needle’s gauge says nothing about how long it is.
- Insulin and pen needles. Pen-needles are outside ISO 6009, so colours seen on them cannot be read from this chart.
- A higher number is thinner. 25G (0.5 mm) is thinner than 21G (0.8 mm).
Related references on this site: 20-gauge needle size, blood draw needle size chart, tuberculin needles and what a hypodermic needle is.
Frequently asked questions
What do the hub colours on needles mean?
Under ISO 6009:2016 each hub colour indicates the nominal outer diameter of a single-use hypodermic needle, for example pink for 18G (1.2 mm) and orange for 25G (0.5 mm). The marked size on the needle or package still has to be checked.
Is hub colour coding required?
ISO 6009 itself does not specify that needles must be colour-coded, or where the colour is applied. Whether a given product uses the code is stated by its manufacturer.
Does this page say which needle size to use with heparin?
No. Sizing for a medicine comes from the medicine’s labelling and the prescriber or facility protocol, not from a colour chart.
How do I convert gauge to millimetres?
Use the chart: 21G is 0.8 mm, 25G is 0.5 mm, 30G is 0.3 mm. These are nominal outer diameters from ISO 6009.
Sources
- ISO 6009:2016, Hypodermic needles for single use – Colour coding for identification, Table 1 (preview): https://cdn.standards.iteh.ai/samples/63277/1a6f149bb0c8466f834702affa19c63b/ISO-6009-2016.pdf (checked 2026-11-01).
- 21 CFR 880.5570, Hypodermic single lumen needle, eCFR: https://www.ecfr.gov/current/title-21/part-880/section-880.5570 (checked 2026-11-01).
