How Does That "Gauging" System Work?
The measuring system for syringe needles is awkward and confusing for most users. The gauge system is used and it has two attributes that make it difficult for most people to use.
- The measure increases with decreasing size. For example, a 30 gauge needle is smaller than a 15 gauge needle.
- The system is not linear. This means that doubling the gauge measure of something does not double (or half, given that the system is inverted) its size.
What Syringe Gauge Measures
The gauge of a syringe is a measure of the needle of the syringe. But there are actually three aspects of the needle that can be measured. First there is the length of the needle. Then there is the outer diameter of the needle and the inner diameter of the needle. The syringe gauge is odd in that it is a measure of both the inner and outer diameter.
Normally, syringes are identified by a number followed by the capital letter "G" followed by a fraction. A typical example is 28G1/2. The "28" is the gauge of the needle--the measure of its diameter. The fraction after the "G" is the length of the needle (just be as consistent as possible) measure in inches. So 28G1/2 is a 28 gauge needle which is a half inch in length.
The table below shows the gauge sizes in millimeters to get a concrete idea of what the gauges really mean.
Typical Injector Sizes
IV and SC injectors normally use syringes with gauges of 27, 28, and 29. IM injectors normally use wider needles such 21 or 23.