Needle Gauge Chart
Gauge (G) describes a needle's outer diameter. The higher the gauge number, the thinner the needle.
| Gauge | Outer diameter (mm) | Outer diameter (inch) | Hub color (ISO 6009) |
|---|---|---|---|
| 18G | 1.27 | 0.0500 | Pink |
| 19G | 1.07 | 0.0421 | Cream |
| 20G | 0.91 | 0.0358 | Yellow |
| 21G | 0.82 | 0.0323 | Deep green |
| 22G | 0.72 | 0.0283 | Black |
| 23G | 0.64 | 0.0252 | Deep blue |
| 24G | 0.57 | 0.0224 | Medium purple |
| 25G | 0.51 | 0.0201 | Orange |
| 26G | 0.46 | 0.0181 | Brown |
| 27G | 0.41 | 0.0161 | Medium grey |
| 28G | 0.36 | 0.0142 | Blue-green |
| 29G | 0.33 | 0.0130 | Red |
| 30G | 0.31 | 0.0122 | Yellow |
| 31G | 0.26 | 0.0102 | — |
| 32G | 0.23 | 0.0091 | — |
Nominal outer diameters for hypodermic tubing per ISO 9626 (rounded). Inner diameter depends on wall type (regular, thin, extra-thin). Colors per ISO 6009; 31G–32G colors are not consistently assigned. Rely on the package label.
How to read a needle label
- Gauge — thickness; higher number = thinner.
- Length — given in inches or mm (½" = 12.7 mm, 1" = 25.4 mm).
- Barrel volume is separate — see the syringe sizes chart.
FAQ
Does a higher needle gauge mean bigger or smaller?
Smaller. Gauge numbers run opposite to size: a 30G needle is much thinner than an 18G needle.
What does a label like 27G × ½" mean?
27 gauge (about 0.41 mm outer diameter) and ½ inch (12.7 mm) long. Gauge and length are independent measurements.
Why are needle hubs different colors?
ISO 6009 assigns a hub color to each gauge so sizes can be recognized at a glance. Always confirm the gauge printed on the package.
What gauge are insulin syringe needles?
Usually in the 28G–31G range, at the thin end of the scale. The exact gauge and length are printed on the box.
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