The Bigger the Gauge, the Smaller the Needle: Needle Gauge Chart (mm)

The bigger the gauge number, the smaller the needle. A 30 G needle is thinner than a 20 G needle, and an 11 G needle is much wider than both. The chart below gives the outside diameter in millimetres for gauges 11 to 30, copied from the international standard for stainless steel needle tubing.

Needle gauge chart (ISO 9626 sizes in mm)

Source: ISO 9626:2016, Stainless steel needle tubing for the manufacture of medical devices, Table 1. The values match the identical national adoption GOST R ISO 9626-2020 (copy of the table, checked 2026-10-29). The standard covers 25 sizes, 10 G (3.4 mm) to 34 G (0.18 mm); this chart shows the 20 rows from 11 G to 30 G.

Gauge	Designated metric size (mm)	Nominal outside diameter (mm)	Maximum outside diameter (mm)
11 G	3.00	2.950	3.150
12 G	2.70	2.650	2.850
13 G	2.40	2.300	2.500
14 G	2.10	1.950	2.150
15 G	1.80	1.750	1.900
16 G	1.60	1.600	1.690
17 G	1.40	1.400	1.510
18 G	1.20	1.200	1.300
19 G	1.10	1.030	1.100
20 G	0.90	0.860	0.920
21 G	0.80	0.800	0.830
22 G	0.70	0.698	0.730
23 G	0.60	0.600	0.673
24 G	0.55	0.550	0.580
25 G	0.50	0.500	0.530
26 G	0.45	0.440	0.470
27 G	0.40	0.400	0.420
28 G	0.36	0.349	0.370
29 G	0.33	0.324	0.351
30 G	0.30	0.298	0.320

Check your product’s labelling. The chart describes the standard’s tubing sizes. The gauge, length and any other markings printed on the package or hub are what identify the product in your hand.

How to read the chart

Find the gauge number in the first column, then read across to the outside diameter. Reading down the table, the gauge rises by one step at a time while the diameter falls: from 2.950 mm nominal at 11 G to 0.298 mm nominal at 30 G. That is the whole rule behind “the bigger the gauge, the smaller the needle”. The standard describes the gauge as the conventional name for the size, and the metric columns tell you what that name means in millimetres.

Gauge describes outside diameter only. Length is a separate marking: BD’s product page for its 25 G needle lists the length separately, as 7/8 in (22.225 mm). A needle is therefore described by two numbers, for example “25 G, 7/8 in”.

Gauge vs millimetres

ISO 9626:2016 gives each gauge a designated metric size and, alongside it, a nominal and a maximum outside diameter. These are not always the same number:

• 20 G is designated 0.90 mm, but its nominal outside diameter is 0.860 mm.
• 14 G is designated 2.10 mm, but its nominal outside diameter is 1.950 mm.
• 21 G, 16 G, 17 G, 18 G, 23 G, 24 G, 25 G and 27 G have a designated size equal to the nominal diameter.
• 23 G has a nominal diameter of 0.600 mm but a maximum of 0.673 mm, a wider tolerance band than its neighbours.

So a chart that gives “20 G = 0.9 mm” is quoting the designated size, while the nominal figure is 0.86 mm. Both come from the same table. When you compare charts from different sources, check which column each one used.

Common mix-ups

The smaller the gauge number, the bigger the needle

This is the same rule read from the other end. An 18 G needle (1.200 mm nominal) is wider than a 25 G needle (0.500 mm nominal). The number counts steps down in size, so it behaves like a rank, not a measurement.

Gauge is not a length

A gauge number says nothing about how long a needle is. Length is stated separately on the packaging.

Hub colours are not a substitute for the gauge number

A colour coding standard exists: ISO 6009, Hypodermic needles for single use, colour coding for identification. Manufacturers’ hub colours should still be checked against the package. For instance, BD’s product page for its 7/8 in. 25 G needle lists the hub colour as blue. Read the printed gauge rather than inferring it from a colour.

Needles, catheters and insulin syringes use their own references

IV catheters are sized by gauge too, but they are a different device with their own colour conventions. See IV catheter gauge selection for catheters, and insulin syringe sizing for syringes with fixed needles.

Where gauge fits in the wider picture

For the parts of a needle and how a needle differs from a syringe, see what a hypodermic needle is and what a syringe is. Needles with attached tubing are covered in what a butterfly needle is. Suppliers list their range under categories such as injection needles.

Frequently asked questions

Is a bigger gauge a bigger or smaller needle?

A bigger gauge number is a smaller (thinner) needle. In ISO 9626:2016 Table 1, 30 G has a nominal outside diameter of 0.298 mm and 11 G has 2.950 mm.

Is a smaller gauge number a bigger needle?

Yes. A 14 G needle (1.950 mm nominal) is wider than a 22 G needle (0.698 mm nominal).

What does needle gauge measure?

Gauge is the conventional name for the outside diameter of the needle tubing. It does not measure length.

Is 25 G exactly 0.5 mm?

The designated metric size and the nominal outside diameter of 25 G are both 0.500 mm, with a maximum of 0.530 mm.

Can I identify a needle’s gauge by its hub colour?

Do not rely on colour alone. A colour-coding standard (ISO 6009) exists, but manufacturers’ products should be checked against the package labelling.

Sources

• ISO 9626:2016, Stainless steel needle tubing for the manufacture of medical devices, Table 1, as published in the identical adoption GOST R ISO 9626-2020: base.garant.ru/400784348 (checked 2026-10-29).
• BD, product page for BD Needle 7/8 in. 25 G: bd.com product page (checked 2026-10-29).
• ISO 6009, Hypodermic needles for single use, colour coding for identification, listed by national standards bodies (title only; the colour table is not reproduced here).