IV Needle and Catheter Gauge Chart: Colours, Flow Rates and Uses

On the Gauge scale, the higher the number, the thinner the device. The colour code is standard (ISO) and identifies the size at a glance. Approximate values for a short IV catheter:

Practical rule: use the smallest cannula (highest number) that meets the indication; large gauges (14–16 G) only when fast flow is needed (trauma, transfusion), because they are more traumatic to the vein.

The flow a catheter allows depends mainly on its gauge and length (Poiseuille's law): the larger the diameter and the shorter the length, the higher the flow. That is why rapid volume resuscitation uses a short, large cannula (14–16 G), not a long, thin central line.

This maximum flow is different from the prescribed drip rate, which is set with the IV set's roller clamp. The gauge sets the flow "ceiling"; the drip is calculated and regulated separately — see how to calculate drops per minute.

In the butterfly / scalp needle, the usual gauges (e.g. 21–25 G) carry the same colour code and are chosen the same way: thinner for difficult veins, paediatrics and geriatrics.

Don't confuse the two size scales:

A 24 G needle is very thin; a 24 Fr catheter is thick. For catheter sizing and the mm conversion, see the French size chart.

For infusion clinics, hospitals and distributors:

Colour code by gauge clearly visible and ISO-compliant, to prevent selection errors.

A gauge range covering from neonatal/paediatric (24–22 G) to adult and fast-flow (18–14 G).

Atraumatic bevel (triple cut), fixation wings on winged sets, and a universal Luer-lock connector compatible with needle-free connectors, IV sets and extensions.

Latex-free and, for paediatrics/oncology, DEHP-free; EO sterilisation; individual packaging.

Certification and traceability: CE / ISO 13485, lot traceability and national registration as required by destination. Request samples of the most-used gauges before quoting volume.

What colour matches each Gauge size?

The standard code is: 14 G orange, 16 G grey, 18 G green, 20 G pink, 22 G blue and 24 G yellow. On the Gauge scale the higher the number the thinner the device, so 24 G (yellow) is very thin and 14 G (orange) is the thickest.

Which IV gauge is used in each case?

Approximately: 14–16 G for trauma, major surgery and massive resuscitation; 18 G for blood products, contrast and the standard adult; 20 G for general fluid therapy; 22 G for small veins, the elderly and paediatrics; and 24 G for neonates and very small veins. Use the smallest gauge that meets the indication.

Does a higher Gauge mean thicker or thinner?

A higher Gauge number means a thinner device. It is the opposite of the French scale used on catheters, where a higher number means thicker. That is why a 24 G needle is very thin and a 24 Fr catheter is thick.

Does the catheter gauge change the infusion speed?

Yes: the gauge sets the maximum possible flow (a 14–16 G allows rapid resuscitation; a 22–24 G, low flows). But the prescribed drip rate is set separately with the IV set's roller clamp. The gauge fixes the flow ceiling; the drip is calculated and regulated separately.