Needles: The Basics


Written by Ingrid Vennonen, UTS Bachelor of Nursing graduate

Most of us can recognise a needle, whether it be a sewing needle to a medical needle. When pursuing a career in nursing, you will need to know the different types of needles available, as it will be part of your role to inject needles into patients.

However, not all needles are the same, and they all have different purposes.

Which needle size and length do I use?

There are many different types of needles that can be found in the workplace. Below is a list of just some of the needles that you can use, based on size (gauge* and length):

  • 25G, 25mm long
  • 25G, 38mm long
  • 23G, 25mm long
  • 23G, 32mm long
  • 21G, 38mm long
  • 18G, 38mm long

*Gauge refers to the thickness, size, or capacity of something, especially as a standard measure.

Generally, needles are referred to by their gauge. The number next to the G on the packaging indicates the gauge size. For instance, in the pictures below, can you find the 25G 1 needle?

Needle_Image1Needle_Image2‘25G 1’ indicates that the needle has a gauge of 25 and a length of one inch.

Why is needle gauge important?

Needle gauge is important for different reasons. Firstly, the higher the gauge (G) of needle, the thinner the needle. If you’re injecting a small amount of medication, a higher gauge needle is a good option. They are also less painful for the patient.

For large amounts of medication, needles with a lower gauge are better. While it may cause patients more pain, it will deliver the injection much faster than a thin, high-gauge option.

Why is the needle length important?

The length of needle will depend on the size of your patient and the injection site. If your patient is a small child, you will generally use a shorter needle in comparison to an adult.

If you are injecting into the patient’s glutes, as you might for a depot injection, the needle length may need to be longer as you are bypassing more subcutaneous fat in this region than you would if injecting into another body part, such as the deltoid (another common site for intramuscular injections).

Are all needles used to inject the patient?

No. Some needles are designed specifically to draw the medication out of a glass bottle. These needles are usually of a lower gauge, and are therefore thicker to ensure ease of drawing up. An example of these kinds of needles is the 18G needle, pictured below. These needles are also blunt on the tip, whereas the needles used to inject patients will have sharp tips to pierce the skin.


What’s the correct needle to use in different situations?

If you’re injecting thick, viscous solution (similar to honey), opt for a lower gauge needle. If you’re injecting a solution low in viscosity, a higher gauge needle would do the job. No more than 2 mL of medication should be injected via the intramuscular or subcutaneous route (Royal Hospital For Women 2017).

For subcutaneous injections (injections into the fatty layer below the skin), a 25-27G 16mm needle at a 45 degree angle to skin plane is used (Department of Health 2018).

For intramuscular injections (injections into the muscle, which is deeper), a 22-25G 25mm at a 90 degree angle to skin plane should be used (Department of Health 2018).

Some medications may also come prepackaged with their own specific recommended needles, such as insulin or epi pens.

Where are common sites for injections?

For subcutaneous injections, sites for injection can include the lateral aspects of the upper arms, anterior and lateral aspect of thighs, abdomen (avoiding a 5cm diameter around the umbilicus), and the superior aspect of the buttock.


For intramuscular injections, sites for injection can include upper outer quadrant of the glute, upper outer thigh or, most commonly used, the deltoid.

Keep in mind, particularly for children under 12 months, the injection sites will vary, particularly for vaccines. Children under 12 months will normally get vaccines in the anterolateral aspect of the thigh, rather than the deltoid muscle. In this age group, the thigh provides comparatively larger muscle mass than the deltoid.

It is also recommended that you consider the mobility status of the patient. For children over 12 months but under 2 years old, it is up to the discretion of the doctor or nurse administering the injection as to where the injection site will be. Generally, the rule is that, if the patient is walking and there is enough mass in the patient’s deltoid muscle, inject there. This is to not deter the child from wanting to walk, especially if the child has just started to learn this important skill.

Additionally, for newborns and infants, the needle size, length and site will vary. It will be up to the specialist administering the medication to make an informed decision.

What might you be injecting?

You might be injecting anything from vaccines, B12 injections and medication, such as depot antipsychotic medication, hormone/fertility medication, antibiotics, insulin, epinephrine for a severe allergy reaction and more!

Remember to always safely dispose of used needles into the yellow puncture proof containers. This prevents needlestick injury or reuse. Likewise, some needles have safety mechanisms, which should also be deployed after use.

Find out more about Nursing at UTS


  • The Royal Women’s Hospital 2017, Clinical Policies, Procedures & Guidelines, RHW, Randwick.
  • Department of Health 2018, Australian Immunisation Handbook, DoH, Canberra.

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