filling a syringe with insulin

​​Injecting yourself with the right dose of insulin is very important. This is why you need to know how to read a syringe.

Parts of an Insulin Syringe

An insulin syringe has three parts: a needle, a barrel and a plunger.

parts of an insulin syringe 
Parts of an Insulin Syringe

  • The needle is short and thin. It is made of a special material that allows the needle to slide through the skin easily with less pain. It comes with a cap to cover and protect it before it is used.
  • The barrel is the plastic chamber that holds the insulin. It is marked with lines (calibrations) on the side. The lines show you how many units of insulin you are injecting.
  • The plunger is the long thin rod that slides up and down the inside of the barrel. Its function is to either draw the insulin into the barrel or push the insulin out of the barrel through the needle. It has a rubber seal at the lower end to prevent insulin from leaking out. The rubber seal is fitted in such a way that it matches the line on the barrel.

Syringes are meant for one-time use. Once used, they must be thrown away in special puncture-proof containers.

Related: Insulin Syringes and Needles

How to Know What Syringe Size to Choose

Insulin syringes come in different sizes.

Syringe Size

Number of Units the Syringe Holds

0.25 ml


0.30 ml


0.50 ml


1.00 ml


The larger the syringe size, the more insulin it can hold.

When choosing the size of a syringe, consider:

  • the number of units of insulin you need, and
  • how well you can see the line markings on the barrel.


Go for the smallest syringe size you can for the dose of insulin you need. This is because the lines on the barrel of small syringes are further apart and easier to see.

Related: Treatment of Diabetes Mellitus

How to Read a Syringe

When measuring the amount of insulin, read from the top ring (needle side), and not the bottom ring or the raised section in the middle of the plunger.

how to read an insulin syringe 
Figure 1: 10 0 unit Insulin Syringe

For example, Figure 1 shows a 100 unit insulin syringe. Each line represents two units of insulin. Therefore the syringe contains 32 units of insulin. As the lines are very close together, this is not the syringe of choice for a person with poor vision.

Now, test yourself with the quiz below to see how well you can read the syringes.

Quiz 1: What is the insulin dose in the 50 unit insulin syringe shown in Figure 2?

how to read a 50 unit insulin syringe
Figure 2: 50 unit Insulin Syringe

Answer: The top ring of the plunger is at 15. Because each line represents 1 unit of insulin, the insulin dose is 15 units.

Quiz 2: What is the insulin dose in the 30 unit insulin syringe shown in Figure 3?

how to read a 30 unit insulin syringe 
Figure 3: 30 unit Insulin Syringe

Answer: The top ring of the plunger is three lines after 15. Because each line represents one unit of insulin, the dose is 18 units of insulin.

If you need help, ask your doctor or nurse to show you how to:

  • choose the size of syringe that is right for you
  • read the calibrations when measuring the dose of insulin needed

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