How Big Is an 18 Gauge Needle? 1.2 mm, Pink Hub (ISO 6009)

An 18 gauge needle has a designated metric size of 1.2 mm, and under the ISO 6009 colour code its hub is pink. This page is a lookup for anyone who needs to read a needle label or check a product listing: the chart comes first, followed by how to read it and what to confirm on the packaging. It is general product information, not medical advice and not guidance on using a needle on a person.

18 gauge needle size at a glance

The table lists the designated metric size and the ISO 6009 hub colour for 18 gauge and the gauges around it, including the ones people most often search alongside it (25 gauge and 29 gauge). Larger gauge numbers are smaller needles, which is why 18 G (1.2 mm) is wider than 25 G (0.5 mm). Our guide to why a bigger gauge means a smaller needle covers that inverse scale in general terms.

Gauge	Designated metric size (mm)	ISO 6009 hub colour
14 G	2.1	Pale green
15 G	1.8	Blue-grey
16 G	1.6	White
17 G	1.4	Red-violet
18 G	1.2	Pink
19 G	1.1	Cream
20 G	0.9	Yellow
21 G	0.8	Deep green
22 G	0.7	Black
23 G	0.6	Deep blue
24 G	0.55	Medium purple
25 G	0.5	Orange
26 G	0.45	Brown
27 G	0.4	Medium grey
28 G	0.36	Blue-green
29 G	0.33	Red

Source: ISO 6009:2016, Hypodermic needles for single use – Colour coding, Table 1 (free preview from iTeh Standards, checked 2026-11-01). Check your product’s labelling: the marked size on the needle or package is what counts.

How to read the gauge number

ISO 6009 defines gauge as a legacy size designation: each gauge corresponds to a designated metric size that sets the limits for the needle’s outer diameter. For 18 G that designated size is 1.2 mm. The standard covers designated metric sizes from 0.18 mm (34 G) to 3.4 mm (10 G) and does not apply to pen-needles, so the figures above are not a guide to insulin pen needle sizes.

The nominal outer diameters behind these sizes are those specified in ISO 9626. Inner diameter and wall thickness are separate properties that this chart does not give, so do not infer one from the other. For the intravenous and catheter side of gauge selection, see intravenous needle gauge size, and for draw needles see blood draw needle size.

Gauge, millimetres and length (1 in, 1.5 in, 2 in)

Gauge describes the width of the needle; length is a separate figure on the label. Listings state both, for example the BD PrecisionGlide 18 G x 1-1/2 in. needle, whose product page gives needle gauge 18 G, needle length 1-1/2 in. and hub colour pink (BD product page, checked 2026-11-01).

• 1 in = 25.4 mm
• 1.5 in (1-1/2 in) = 38.1 mm
• 2 in = 50.8 mm

These are plain inch-to-millimetre conversions. Which lengths exist for a given gauge is set by each product, so read the length on the label rather than assuming it from the gauge. Searches such as “25g needle 1.5 inch” combine two separate figures: 25 G is 0.5 mm with an orange hub in the table above, and 1.5 in is 38.1 mm of length. A “3 mL syringe needle” or a “1 in needle” likewise names a syringe volume or a length, neither of which tells you the gauge; the gauge is marked on the needle’s own packaging.

Hub colour code by gauge

ISO 6009 gives each designated metric size a colour so a needle can be recognised at a glance. The colours may be opaque or transparent and are referenced through RAL or Pantone shades, so the exact tone varies between makers. The standard does not itself require needles to be colour-coded or say which part of the needle or package carries the colour; that is left to product standards. Our guide to 20 gauge needle size shows the same lookup for yellow.

Common mix-ups

Several colours are reused across the full gauge range, so colour alone does not identify a needle. ISO 6009 itself says colour coding does not absolve the user of the responsibility to check the marked size.

• Orange: 25 G (0.5 mm) and 34 G (0.18 mm).
• Yellow: 20 G (0.9 mm) and 30 G (0.3 mm).
• Black: 22 G (0.7 mm) and 33 G (0.2 mm).
• Deep green: 21 G (0.8 mm) and 32 G (0.23 mm).
• White: 16 G (1.6 mm) and 31 G (0.25 mm).

Pink, the 18 G colour, appears once in the table, but treat it as a cross-check rather than an identifier.

What to check on the label

1. The gauge marked on the packaging (for example 18 G).
2. The length marked on the packaging, in inches or millimetres.
3. The hub colour, as a cross-check against the ISO 6009 table above.
4. The maker’s own product listing, which states gauge, length and hub colour as in the BD example.

If a listing and the packaging disagree, go by the marked size and ask the supplier. Check your product’s labelling.

Frequently asked questions

How big is an 18 gauge needle?

Its designated metric size is 1.2 mm under ISO 6009:2016 Table 1, with a pink hub colour. That is the standard’s designation for the gauge, not a measured value for any single product.

Is a 25 gauge hypodermic needle bigger or smaller than 18 gauge?

Smaller. A 25 G needle is 0.5 mm with an orange hub, against 1.2 mm for 18 G.

How big is a 29 gauge needle?

29 G has a designated metric size of 0.33 mm and a red hub in ISO 6009 Table 1. Pen-needles are outside the scope of that standard.

How long is a 2 inch or 1 inch needle?

2 in is 50.8 mm and 1 in is 25.4 mm. Length is stated separately from gauge, so read both on the label. For conversions between catheter units see French to mm conversion.

Sources

• ISO 6009:2016, Hypodermic needles for single use – Colour coding, Table 1, scope and introduction, preview PDF at cdn.standards.iteh.ai (checked 2026-11-01).
• BD, 18 G x 1-1/2 in. BD PrecisionGlide Needle product page, bd.com (checked 2026-11-01).