Insulin Needle Sizes

Taking insulin is part of everyday life for many people with diabetes. While there’s different ways to take insulin, the traditional syringe is still widely used today. But syringes come in different insulin needle sizes that can impact the comfort insulin injections. We take a close look at insulin syringes and needles, how they’re different from others, and what it means for your diabetes self care.

Basics of Insulin Syringes

An insulin syringe is one of the most common ways to take insulin. And it’s also what most think a person with diabetes uses to take insulin. Other ways are using an insulin pen, pump and even with an inhaler.

A typical syringe will have three parts: the barrel, plunger and needle.

  1. Barrel: this is the body of the syringe and where the fluid is stored. It’s usually made of clear plastic and marked with the volume measurements.
  2. Plunger (or piston): this enters the barrel and is what injects out or pulls in liquid into the syringe. It’s usually made of plastic and has a rubber tip or gasket to create a seal.
  3. Tip: this is what holds the needle and can either be removable or fixed onto the syringe.
  4. Cap: this is what covers the needle for protection and come in different colors.
diagram showing parts of a syringe

How Insulin Syringes Differ from Other Syringes

Insulin syringes differ slightly from other syringes like those used to give other medications or as part of IVs.

One big difference with insulin syringes is that the needles are usually attached and not detachable. While other needles are often detachable like the ones used for catheters or IVs.

hand holding insulin
Insulin syringe with attached needle

Another difference is that insulin syringes often have an orange cap, which manufacturers generally use to identify the needle gauge. But color coding needles is not an official standard so always make sure you’re using the right needle.

Insulin Syringe Sizes

Like other syringes, insulin syringes come in multiple sizes to give different doses.

The size or capacity is marked by the units of insulin in the syringe. Each unit equals an amount of insulin measured in millimeters (mm), which depends on the concentration.

U-100 syringes are most commonly used and when used with a U-100 insulin vial, it comes out to the following:

  • 30 units = 0.3mL
  • 50 units = 0.5mL
  • 100 units = 1mL

Sizes of Insulin Needles

The size of needle means the thickness and length. Thickness is measured by gauge and length measured by millimeters or inches.

The most common needle size for insulin syringes is 12.7 mm or 1/2″. The other lengths available are 8 mm (5/16″), 6 mm (15/64″) and 5 mm (3/16″).

insulin needle length comparison

Insulin needles are also pretty thin and are in the 31 – 29 gauge range.

Why Needle Gauge and Length are Important

A smaller gauge size means a thicker needle, while a higher gauge means it’s thinner. And needle length is measured in inches or millimeters.

Thick Needles Inject More Fluid

Because needles are hollow, a thicker needle has a larger inside diameter. This allows it to inject more fluid compared to thinner needles.

For instance, needles used for IVs are thicker needles in the 22 – 21 gauge because it’s meant to deliver more fluid. But the extra thickness can be uncomfortable or a little painful.

But insulin syringes inject only a small amount of liquid so it uses thinner needles in the 31-29 gauge range. And needles that are thinner generally have less pain.1

Shorter needles are for Just Under the Skin

The length of a needle determines how deep it will go in your body.

So longer needles are used when the injection needs to go into the muscles. This is called an “intramuscular” injection.

And a shorter needle is meant when you only need to be just below the skin and not into the muscle. This is called a “subcutaneous” injection and is what insulin syringes use.

For comparison, needles used to give an epidural during child delivery is usually about 3 1/2″ long in order to reach the spine.

But the needle on an insulin syringe is less than 1″ long because it just needs to go below skin thickness and into fatty tissue.

Insulin Needle Length Selection

Most people can use the common 1/2″ insulin syringe needle size with no problems at all. There’s also not a big difference between these needle lengths so there’s really not one “right needle length.”

But you may have certain needs and there’s some factors to consider when picking a needle length.

Some prefer a shorter needle which can be more comfortable and have less pain. Also, children may have to use short needles because they have less fatty tissue.

If you something evening shorter, you may want to try using an insulin pen because insulin pen needles are only 4mm length. Also, pen needles are generally easier to use than syringes and can be better option you have shaky hands or arthritis.

How to Use an Insulin Syringe

Below are the basic steps on how to prepare an insulin syringe and inject insulin. But always check the instructions from your care provider.

man inserting syringe in insulin vial

Preparing the Syringe

  1. Remove the cap from the insulin vial and roll it between your hands for a few seconds. This mixes the insulin and slightly warms it (which is more comfortable when injecting).
  2. Wipe the top of the bottle with an alcohol pad.
  3. Draw air into the syringe by pulling the plunger to the number of units of your dose. This is needed to inject the same amount of air into the vial as the dose of insulin you’ll remove.
  4. Insert the needle into the vial and push the plunger down to inject the air.
  5. Turn the vial and syringe upside-down. Make sure the insulin covers the needle so you’re not just drawing air.
  6. Pull back the plunger to the number of units of your dose.
  7. Check the syringe for air bubbles. If there’s any, push the plunger back in and re-draw the dose.
  8. Remove the syringe from the vial and now you’re ready to inject.

Insulin Injection

  1. Choose an injection site (usually the abdomen area, outer thigh or upper arm) and wipe with an alcohol pad.
  2. Hold the syringe barrel like a pen (needle end down). Be careful not to push the plunger.
  3. Take your other hand and gently pinch a 2″ to 3″ fold of skin of the injection site.
  4. With a quick motion, insert the needle all the way down into the pinched skin at a 90-degree angle.
  5. Push the plunger until all of the insulin is out of the syringe. Leave in for about 10 seconds.
  6. Pull out the syringe. Wipe any bleeding with an alcohol wipe and use a bandage, if needed.
woman injecting insulin into abdomen

Rotating Injection Sites

Because you’ll be injecting insulin regularly, you don’t want to inject at the same site for the next dose.

Using the same injection site over and over again can harden the skin and can become uncomfortable. It can also keep the insulin from being fully absorbed.

Instead, rotate to different injection sites for each dose to make injecting easier and more comfortable.


Is there a diabetes needle size?

There’s no one standard needle size used for diabetes insulin injections. But the 1/2″ needle is the most common used for insulin syringes.

What is the smallest needle for insulin?

The smallest insulin syringe needles are 6mm (15/64″). But an insulin pen needle is even smaller at 4mm.

Do shorter needles leak more than longer needles?

There’s some concern that short needles are more prone to leaking than longer one. But studies found there was no major difference in leakage between the lengths. Actually, the research saw that insulin leakage is more likely from not injecting the needle correctly.


Insulin syringes are still the most common way to take insulin so it’s good to learn about your syringe and needle size. The basic parts of an insulin syringe are the barrel, plunger and needle, which usually comes attached to the syringe.

Insulin needles come in different lengths and thicknesses. Thickness is measured in gauges with a higher gauge meaning a thinner needle, and vice versa. And the length of needs are measured in millimeters or inches.

While there is no standard insulin needle size, the 1/2″ (12.7mm) needles are widely used and people generally have no issues with them. But they also come in smaller sizes of 8mm and 6mm, and even 4mm used in insulin pens.

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