Needle gauge chart
A needle's gauge is a size number for its outside diameter, and BD's technical data sheet gives the range for each gauge it makes, from 16 G to 30 G.[1]
| Gauge | Wall | Outside diameter (mm) | Outside diameter (in) | Inside diameter, min (mm) |
|---|---|---|---|---|
| 16 G | thin | 1.600–1.690 | 0.063–0.067 | 1.283 |
| 18 G | thin | 1.200–1.300 | 0.047–0.051 | 0.910 |
| 21 G | thin | 0.800–0.830 | 0.032–0.033 | 0.547 |
| 23 G | thin | 0.600–0.673 | 0.024–0.027 | 0.370 |
| 25 G | thin | 0.500–0.530 | 0.020–0.021 | 0.292 |
| 27 G | regular | 0.400–0.420 | 0.016–0.017 | 0.184 |
| 30 G | regular | 0.298–0.320 | 0.012–0.013 | 0.133 |
All values are BD's own minimums and maximums; BD converts with 1 mm = 0.03937 in.[1]
Higher gauge means a thinner needle
A bigger gauge number means a smaller needle. In the chart an 18 G needle is about four times as wide as a 30 G needle (1.2 mm against 0.3 mm), and each step up the scale is narrower than the one before. A “25 or 30 gauge” question is therefore easy: 25 G (0.5 mm) is the thicker one.
- 16–18 G: 1.2–1.69 mm, the widest in BD's chart.
- 21–23 G: 0.6–0.83 mm.
- 25–27 G: 0.4–0.53 mm.
- 30 G: 0.298–0.32 mm, the finest in BD's hypodermic chart.
Needle sizes by gauge: 18 G to 31 G
Each gauge below has BD's outside diameter where BD lists it, and where that gauge turns up in published guides and product sheets. 22 G and 31 G are not in BD's hypodermic data sheet, so no diameter is given for them.
18 gauge needle
An 18 gauge needle is 1.2–1.3 mm (0.047–0.051 in) across, with an inside diameter of at least 0.91 mm in BD's thin-wall range.[1] Only 16 G is wider in that chart.
21 and 22 gauge needles
A 21 gauge needle is 0.8–0.83 mm across.[1] A 22 gauge needle sits between 21 G and 23 G; BD's sheet has no row for it. CDC's vaccine guide gives 22–25 G as the needle gauge for intramuscular injection.[7]
23 and 25 gauge needles
A 23 gauge needle is 0.6–0.673 mm across and a 25 gauge needle 0.5–0.53 mm.[1] For vaccines given under the skin, CDC describes a ⅝-inch, 23- to 25-gauge needle.[7] BD sells a 3 mL syringe with a 25 G × 1 in. needle attached.[6]
27 gauge needle
A 27 gauge needle is 0.4–0.42 mm across, a regular-wall needle in BD's chart.[1] embecta pairs 27 G with its 12.7 mm (½ in) insulin syringe needle.[2]
30 and 31 gauge needles
A 30 gauge needle is 0.298–0.32 mm across, the finest in BD's hypodermic chart.[1] 31 G is finer still and appears on embecta's 6 mm and 8 mm insulin syringes.[2]
Needle sizes: gauge × length
A needle size is written as gauge × length, for example 25 G × 1 in. on a BD 3 mL syringe with an attached needle.[6] BD groups its conventional needles into lengths of 1 inch or less and 1¼ to 1½ inch, and converts with 1 in = 25.4 mm.[1]
| Length (mm) | Length (in) | Where it appears |
|---|---|---|
| 6 | 0.24 | Shortest embecta insulin syringe needle |
| 8 | 0.31 | embecta insulin syringes |
| 12.7 | 0.50 | embecta insulin syringes (½ in) |
| 25.4 | 1.00 | BD 25 G × 1 in. needle |
| 31.8–38.1 | 1.25–1.50 | BD’s longer conventional needles |
Insulin needle sizes and insulin needle length
Insulin syringe needles are 27 G to 31 G and 6 mm to 12.7 mm long. embecta's U-100 syringes come with five combinations: 12.7 mm × 27 G or 29 G, 8 mm × 30 G or 31 G, and 6 mm × 31 G, the shortest syringe needle it offers.[2][3]
| Length | Gauge |
|---|---|
| 12.7 mm (½ in) | 27 G or 29 G |
| 8 mm | 30 G or 31 G |
| 6 mm | 31 G |
embecta's injection guide states that a 6 mm insulin syringe, or a 4 mm pen needle, is the recommended length for all patients and all injection sites,[4] and notes that children aged 6 or under and very thin adults may need a pinch-up.[5] Which needle you use is your prescriber's decision.
What gauge needle for insulin?
Insulin syringe needles in embecta's range are 27, 29, 30 or 31 gauge,[2] and BD's chart puts 27 G at 0.4–0.42 mm and 30 G at 0.298–0.32 mm.[1] The needle does not change the scale: a U-100 syringe reads the same whatever needle it carries. See insulin syringe sizes for the barrels.
Worked needle size conversions
Convert needle sizes with BD's factors: mm × 0.03937 = inches, inches × 25.4 = mm.[1]
- A 25 G × 1 in. needle is 0.5–0.53 mm wide and 25.4 mm long.
- A 6 mm insulin syringe needle is about 0.24 in long.
- A 12.7 mm needle is exactly ½ in (12.7 ÷ 25.4).
Common needle size mistakes
- Thinking a bigger gauge is a bigger needle. It is the opposite: 30 G is narrower than 25 G.
- Judging by hub colour. Colours are not consistent across makers; read the printed size.[1]
- Mixing up length and gauge. “6 mm × 31G” is length × gauge; the gauge does not tell you the length.
Hub colours
Needle hubs are colour-coded, but do not rely on colour alone. BD lists ISO 6009 as its colour standard and notes that its 16 G and 25 G PrecisionGlide needles in the U.S. do not follow it.[1] Read the gauge and length printed on the pack.
How we checked these numbers
The chart is BD’s own data sheet (BD-56356, 09/24) copied value by value, and the CSV below is generated from the same table. The conversions use BD’s factors and can be checked by hand.
| Input | Expected | Basis |
|---|---|---|
| 25 G outside diameter | 0.5–0.53 mm = 0.020–0.021 in | BD-56356 table |
| 12.7 mm | 0.50 in | 12.7 ÷ 25.4 |
| 1 in needle | 25.4 mm | BD conversion factor |
| 18 G vs 30 G | 18 G about 4× wider | 1.2 ÷ 0.298 |
Known limits.
- Diameters are BD’s; other makers publish their own tolerances.
- 22 G and 31 G are not in BD’s hypodermic sheet, so no diameter is given for them.
- Gauge and length do not tell you which needle to use; that is your prescriber’s call.
Download the data. BD needle gauge chart, mm and inches (CSV)
Change log.
- : Gauge-by-gauge sections (18 G to 31 G) and CSV download added.
RelatedThe rest of the syringe is labelled in parts of a syringe; general syringe capacities are in the syringe sizes chart and 3, 5 and 10 mL syringes.
Frequently asked questions
Is a higher gauge needle bigger or smaller?
Smaller. A 30 G needle is about 0.3 mm across; an 18 G needle is 1.2–1.3 mm.
Is 25 or 30 gauge thicker?
25 G is thicker: 0.5–0.53 mm against 0.298–0.32 mm for 30 G in BD’s data.
What size needle is on an insulin syringe?
In embecta’s range, 6 mm × 31 G, 8 mm × 30 or 31 G, or 12.7 mm × 27 or 29 G.
How long is a 1 inch needle in mm?
25.4 mm.
How big is an 18 gauge needle?
1.2–1.3 mm across in BD’s data, about four times the width of a 30 G needle.
Is a 22 gauge needle bigger than a 25 gauge?
Yes. A lower gauge is wider, so 22 G is thicker than 25 G (0.5–0.53 mm).
What syringe needle gauge is the thinnest?
In BD’s hypodermic chart, 30 G (0.298–0.32 mm). embecta insulin syringes go to 31 G.
Sources
- BD disposable hypodermic needles: technical data sheet (BD-56356)
- Technical data sheet: insulin syringes (Micro-Fine, Ultra-Fine)
- Insulin syringes with Ultra-Fine needle
- Injection technique guide: how to inject insulin with a syringe
- How to inject with BD SafetyGlide insulin syringe with a 6 mm needle
- 3 mL BD Luer-Lok syringe with attached needle 25 G × 1 in. (product 309581)
- Vaccine administration (Best Practices for Immunization)