How to Read Insulin Syringe Units

reading insulin syringes
person holiding an insulin syringe

An insulin syringe is a special syringe designed for injecting insulin. It allows people with diabetes to accurately measure and administer their insulin dose.

Using the correct syringe size and understanding the measurement units are important to ensure you inject the precise amount of insulin prescribed by your doctor.

In this guide, we’ll discuss how to read an insulin syringe. 

Parts of an Insulin Syringe

An insulin syringe has 3 main parts – the needle, barrel, and plunger. Understanding the role of each part can help you use the syringe correctly.

  • Needle – The needle is used to inject insulin under the skin. It’s usually very thin, short, and fine to minimize discomfort.
  • Barrel – The barrel holds the insulin. It is typically clear and has markings to measure the insulin dose. The barrel connects to the needle at the tip.
  • Plunger – The plunger is used to draw insulin into the barrel and push it out for injection. The rubber gasket on the plunger creates a seal inside the barrel to hold the liquid medication.
  • Scale – The scale has measurement markings that indicate the dose of insulin to be injected. The scales can differ based on the syringe capacity and insulin concentration. Common scales are in unit markings from 1 to 100.

Types of Insulin Syringes

There are a few different types and sizes of insulin syringes that are commonly used. The main options are:

Syringe Size

The three most common insulin syringe sizes are 0.3 mL, 0.5 mL, and 1 mL. The size refers to the maximum amount of medication the syringe can hold. 0.5 mL and 1 mL syringes are the most widely used.

  • 0.3 mL syringes are good for pediatric use or when a small dose of insulin is needed.
  • 0.5 mL syringes allow accurate measurement of doses between 30 and 50 units.
  • 1 mL syringes are useful when large doses of insulin, over 50 units, are required.


Needle Gauge

Insulin syringes come with different needle gauges – the most common are:

  • 31 gauge ultra-fine needle – this is the thinnest needle option. It provides nearly painless injections.
  • 30 gauge ultra-fine needle – slightly thicker than 31 gauge but still very thin and comfortable.
  • 28 and 29 gauge standard needles – the most common needle sizes for insulin. 


Insulin Concentrations

Insulin syringes come in two main concentrations: U100 and U40.

  • U100 syringes contain 100 units of insulin per mL. This is the most common type of insulin syringe used today.
  • U40 syringes contain 40 units of insulin per mL. U40 syringes used to be more common but have been largely phased out in favor of U100 syringes.

The concentration of the syringe must match the concentration of the insulin vial you are using. Most insulin vials today have U100 concentrations. It’s important to always double check that you have the right syringe for the insulin vial; otherwise, you could end up with the wrong dose.

For example, if you are using a U100 insulin vial, you must use a U100 syringe. Using a U40 syringe with a U100 insulin vial would result in you drawing up the wrong dose. The markings on a U40 syringe are different than those on a U100 syringe.

Reading the Scale

The insulin syringe scale is marked with lines and numbers indicating the dose volume. The lines and numbers allow you to measure and draw up the precise insulin dose prescribed by your doctor.

There are two main types of scale markings:

  • Large Increment Syringes: These have scale lines marked every 1 unit. The numbers indicate the number of units (10, 20, 30, etc.). These are the most common types of insulin syringes.
  • Small Increment Syringes: These have smaller lines between the major unit lines, allowing for half-unit doses. The scale will have lines at 0.5 unit increments.


When drawing up the dose, it’s important to line up the plunger with the line that corresponds to the prescribed dose.

For example, if your dose is 15 units, draw the plunger up to the line marked 15. If your dose is 17.5 units, draw up to the line exactly halfway between the lines marked 17 and 18.

If you guess or estimate “close enough,” this can lead to overdosing or underdosing insulin, which is dangerous.

Final Remarks

Reading insulin syringes accurately is extremely important for managing diabetes. Even small errors in drawing up or injecting insulin can lead to dangerously low or high blood sugar levels. 

Always take your time, double check your dosage calculations, and follow safety procedures closely. With practice and care, you can become proficient at using syringes and get the right insulin dose every time.