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General product information only, not medical advice. Choosing a needle for a person or a procedure is a decision for a trained clinician following the manufacturer’s instructions for use.
A 20 gauge needle has a designated metric size of 0.9 mm, and under ISO 6009 its hub colour is yellow. Gauge is a legacy label: the higher the number, the thinner the needle, so 20 G sits between the thicker 18 G (1.2 mm) and the thinner 22 G (0.7 mm). The chart below puts the 20 G row next to its neighbours. For the full 10 G to 34 G scale see the bigger the gauge, the smaller the needle and intravenous needle gauge size.
20 gauge needle size chart (18 G to 22 G)
Designated sizes and colours are from ISO 6009:2016, Table 1. The minimum and maximum outside diameters are the ISO 9626:2016 tubing limits for each size (Table 1, columns ODMIN and ODMAX). Both standards are listed under Sources.
| Gauge | Designated metric size (mm) | Minimum outside diameter (mm) | Maximum outside diameter (mm) | ISO 6009 hub colour |
|---|---|---|---|---|
| 18 G | 1.2 | 1.200 | 1.300 | Pink |
| 19 G | 1.1 | 1.030 | 1.100 | Cream |
| 20 G | 0.9 | 0.860 | 0.920 | Yellow |
| 21 G | 0.8 | 0.800 | 0.830 | Deep green |
| 22 G | 0.7 | 0.698 | 0.730 | Black |
Check your product’s labelling. The gauge and length printed on the pack or hub identify the product in your hand. Needle length is not part of these charts and is not set by the gauge.
How to read the 20 G row
Three different numbers get called “the size of a 20 gauge needle”, which is why charts disagree. 0.9 mm is the designated metric size, the label for the gauge. The outside diameter of the tubing may fall anywhere from 0.860 mm (the minimum) to 0.920 mm (the maximum) allowed for that size. A source quoting “0.9 mm” and one quoting “0.86 mm” are usually describing the same needle with different columns.
Gauge, millimetres and other labels
ISO 6009 describes gauge as a legacy size designation and uses the metric size as the designation. Its colour code runs from 34 G (0.18 mm) to 10 G (3.4 mm). The standard establishes the colour code but does not itself require that needles be colour-coded, or say which part of the needle or pack carries the colour. Its stated purpose is rapid visual identification of the outside diameter of single-use hypodermic needles. It does not apply to pen needles; see insulin pen needle sizes for those.
Common mix-ups: yellow is 20 G and 30 G
Colours in the ISO 6009 table repeat across the range, so a hub colour alone does not name a gauge. Reading directly from Table 1:
- Yellow is 20 G (0.9 mm) and also 30 G (0.3 mm).
- Black is 22 G (0.7 mm) and 33 G (0.2 mm).
- Deep green is 21 G (0.8 mm) and 32 G (0.23 mm).
- White is 16 G (1.6 mm) and 31 G (0.25 mm).
- Orange is 25 G (0.5 mm) and 34 G (0.18 mm).
The standard says the presence of colour coding on a needle or package does not absolve the user of the responsibility to check the marked size of the needle.
Label checklist when specifying a 20 gauge needle
Items printed on the pack that identify a 20 gauge needle:
- The marked gauge (20 G) and the designated size, if printed.
- The needle length, printed separately from the gauge.
- The hub colour, as a visual aid only. Yellow also appears on 30 G needles.
- Whether the product is a standalone needle or a needle-and-syringe pack, and whether the labelling states it is single-use.
Related sizes people look up
18 gauge needle and 18 gauge syringe
18 G is two steps up from 20 G, with a designated size of 1.2 mm and a pink hub colour in ISO 6009. A pack described as an 18 gauge needle with syringe gives the gauge of the needle only; the syringe is labelled by its own volume. See what is a hypodermic needle for the device itself.
20 gauge needle and syringe
The same applies to a 20 gauge needle and syringe: 0.9 mm designated, yellow hub, with syringe volume stated separately on the pack.
31 gauge needle and 31 gauge insulin needles
31 G has a designated size of 0.25 mm and a white hub colour in ISO 6009, far thinner than 20 G. Insulin pen needles are outside the scope of ISO 6009; for insulin syringes see insulin syringe sizing, needle gauge and volume.
18 and 20 gauge spinal needles
Spinal and epidural needles are labelled on the same gauge scale, so a 20 G spinal needle has the same designated diameter as any other 20 G needle. Gauge says nothing about length, which comes from the product’s own labelling. Our page on the Quincke needle describes one such device.
FAQ
How big is a 20 gauge needle in mm?
Designated metric size 0.9 mm. The tubing’s outside diameter is permitted to range from a minimum of 0.860 mm to a maximum of 0.920 mm.
What colour is a 20 gauge needle hub?
Yellow under ISO 6009:2016, when the manufacturer applies the colour code. The standard does not require colour-coding, and yellow is also the 30 G colour.
Is a 20 gauge needle bigger than an 18 gauge?
No. 18 G (1.2 mm) is thicker than 20 G (0.9 mm). A lower gauge number means a wider needle.
Does gauge tell me the needle length?
No. Gauge describes diameter. Length is printed separately on the labelling.
Sources
Checked 2026-11-01.
- ISO 6009:2016, Hypodermic needles for single use: Colour coding for identification, Table 1 and Introduction: https://www.iso.org/standard/63277.html (preview text: https://cdn.standards.iteh.ai/samples/63277/1a6f149bb0c8466f834702affa19c63b/ISO-6009-2016.pdf).
- ISO 9626:2016, Stainless steel needle tubing for the manufacture of medical devices: Requirements and test methods, Table 1: https://www.iso.org/standard/60480.html (preview text: https://cdn.standards.iteh.ai/samples/60480/171ac3e265714abdb42e7adb03381b92/ISO-9626-2016.pdf).
