Syringe gauges, specifically referring to needle gauges, are measured using a numerical system where a higher gauge number indicates a smaller needle diameter. This means a 25-gauge needle is smaller than a 22-gauge needle. The gauge number is based on the size of the hole in the needle, not the outer diameter. This system is internationally used and is often simply referred to as "Gauge" or "G".
Understanding the Gauge System
The gauge system is inversely proportional; a higher number means a smaller diameter. This is important because different gauge needles are suitable for various injections depending on viscosity and injection site.
- Higher Gauge (e.g., 27G, 30G): Smaller diameter, less bleeding, better for subcutaneous injections (under the skin).
- Lower Gauge (e.g., 18G, 22G): Larger diameter, potentially more bleeding, better for intravenous injections (into a vein) due to faster fluid delivery.
The needle's length is also crucial and is usually specified along with the gauge (e.g., 25G x 1/2").
Examples from different sources illustrate this:
- A reference mentions a 26-gauge needle having an outer diameter (O.D.) of 0.46 mm and an inner diameter (I.D.) of 0.26 mm, while a 26s gauge needle has a slightly larger O.D. of 0.47 mm and an I.D. of 0.26 mm. Hamilton Syringe Needle Gauge Chart
- Another source highlights that the gauge refers to the needle's hole size: the higher the gauge, the smaller the hole. Needle Gauge Resource List
It is important to note that syringe capacity (the amount of liquid it holds) is measured in milliliters (mL) or cubic centimeters (cc). This is separate from the needle gauge. Insulin syringes, however, are often measured in units.
