Four central delivery systems for insulin are currently available: syringes, pens, pumps, and inhalers. How people take insulin can change depending on their lifestyle, sugar levels, and diet.

Insulin syringes are used to administer insulin using a needle and come in various sizes to accommodate multiple insulin doses, levels of comfort, and price points.

This article will discuss the various sizes of insulin syringes and insulin needle length selection.

What is a Pen Needle?

You attach pen needles to a sturdy or prefilled pen so you may inject the medication.

Standard and safety pen needles are common, with standard pen needles being the most widely used.

A standard pen needle features a removable outer and inside needle cover. Both must be eliminated before insulin can be released.

The safety needle is unique. Before injections, the outside cover is removed, but not the interior cover.

The inside cover of the safety needle glides back to reveal the needle when you insert it into your skin. Because the inner cover is left in place, you are shielded from unintentionally sticking yourself with the needle. If you're afraid of needles (since you won't ever see the actual needle) or worried that you'll inadvertently poke yourself with the needle, this sort of needle is perfect for you.

Different Insulin Pen Needle Sizes and Insulin Syringe Sizes

Diabetes Insulin Pen Needle Sizes

Needles for insulin pens come in various lengths ranging from 4 mm to 12.7 mm (5/32 inch to 0.5 inches). The medical system tends to favor using shorter needles, but in the end, you must determine which needle size is ideal for you.

Being given a longer needle can make your first insulin injection feel intimidating and may even make you less likely to take your medication as directed.

If so, kindly contact your doctor and ask for a different needle. Alternatively, if your state doesn't require a prescription (more on that later), buy a size that works for you online or at your neighborhood pharmacy.

Importance of Length and Needle Gauge

It's crucial to select a length and gauge for the needle you feel comfortable with.

A person's size does not affect the effectiveness or likelihood of insulin leakage when using shorter needles. In addition, there is probably not much individual variation in skin thickness.

People are more likely to prefer shorter needles. Generally, using needles of 4 to 8 mm in length is advised.

The needle thickness is also an essential factor. You might prefer thinner needles since they are often less uncomfortable, easier to handle, and easier to insert than thicker ones.

While persons with diabetes must use the correct needle size and needle thickness, it's crucial that they give the insulin correctly and alternate injection sites to maintain their blood sugar and prevent problems.

How to Choose the Perfect Insulin Needle Sizes?

You should select a needle that makes it the simplest to inject insulin and GLP-1s subcutaneously (into the fat between your skin and your muscle).

Despite body size, gender, ethnicity, and BMI, the average thickness of human skin is between 1.9 and 2.4 mm. As a result, subcutaneous tissue will vary in thickness between individuals. Accordingly, a short 4- or 5-mm needle should work for all body types.

According to the International Scientific Advisory Board, there is no medical justification for recommending a needle length greater than 8 mm. Regardless of B.M.I., the board advises using 4-, 5-, and 6-mm needles for all adult patients.

That doesn't imply you can't use a longer needle, but doing so raises the possibility of bleeding, pain, and bruises.

You run the additional danger of injecting your insulin into the muscle using a larger needle (called an intramuscular injection). Insulin can absorb excessively quickly if administered into muscle rather than fatty tissue, which might result in low blood sugar levels. Avoid intramuscular injection.

Even though shorter needles are typically preferred, there are several situations where a longer needle is preferable.

For instance, if you struggle with coordination due to diseases like Parkinson's disease or arthritis, you can benefit from using a longer needle.

Generally, it's best to use a needle as short and thin as you feel comfortable using. Injections that hurt more than needed will probably be made using thicker needles.

The barrel size will generally depend on a person's dose; different doses may require different diameters. It is best to pick a size that enables a person to take each dose at once. For instance, measuring a 10-unit dose using a 30-unit insulin syringe and a 55-unit dose with a 100-unit insulin syringe could be more straightforward. The barrel's size determines a syringe's capacity for insulin, while the needle's gauge determines the needle's thickness.

How to Safely Inject Insulin?

A subcutaneous injection is required to deliver insulin to the layer of fat beneath the skin because the body breaks down insulin with the help of digestive enzymes. The insulin can then gradually be absorbed into the bloodstream, where it travels to all the body's cells.

A person should do the following before injecting insulin into a syringe:

Gather supplies

After cleaning your hands, you should get a new needle and an insulin vial. They can verify that they have the proper type of insulin and that it is up-to-date and particle-free. The insulin may also need to be gently mixed.


Sterilize the vial's top with an alcohol swab after removing the protective covering from the insulin vial.

Prepare insulin syringes

To prepare the insulin syringe, remove the needle's cap and pull the plunger back until it is the correct depth for the patient's dose. Push the plunger to inject the air after inserting the needle through the rubber cap of the vial. Turn the bottle and syringe upside down while keeping the needle in the vial. To take the desired dose, pull the plunger.

Examining the syringe

A person should inspect the syringe for bubbles before removing the needle. If there are bubbles, tap the syringe's side until the bubbles rise to the top. Once the syringe contains the proper dosage, use the plunger to force the bubbles out and pull them back in.

Removing the needle

The needle can now be taken out of the vial without risk. Before injecting, they should make sure the needle has not touched anything.

Now a person is prepared to administer the insulin. The arms' stomach, hips, thighs, buttocks, and backs are among the usual injection sites. To give insulin injections, one should: 

Choose an injection site

Decide where to place the insulin injection . To avoid injecting in the same skin area too often, the injection site should ideally be different from the prior one. After making a choice, one should use an alcohol wipe to disinfect the spot.

Pinch the skin

The skin and fatty tissue between the thumb and first finger must be pinched once the area has been cleaned.

Insert the needle

At this point, the needle can be quickly inserted into the pinched skin. The patient can unwind and release the skin when the needle is placed.

Inject the insulin

With the needle in place, the plunger can now be slowly depressed to administer the prescribed amount of insulin. One should leave the needle in the skin for five seconds after giving the dose.

Removing the needle

To stop any insulin from leaking out, one can draw the needle straight out while applying light pressure to the injection site. Avoid rubbing the area.

How to dispose of insulin syringes

Once it has been used, the needle should be put in a sharps container or another secure location. The medical waste can subsequently be disposed of following the requirements of the local sanitation department.

Concerns Around Leakage

Some people have expressed concern that short needles will not be acceptable for those with larger bodies or will cause insulin leakage (insulin not being properly administered).

Shorter needles are effective for most body types and cause no more leakage, contrary to the myth that had propagated.

However, you should use a longer needle if that makes you feel more comfortable.

Where to Buy Insulin Needles?

The short answer to whether one can purchase pen needles over the counter is that it depends.

In the U.S., state-by-state prescription laws vary, and in some places, you can buy pen needles without a prescription.

However, they could need a prescription if you pay for your needles with insurance.

You can also purchase pen needles online without a prescription.

How to Choose the Correct Insulin Needles

In the United States, syringe insulin injections are still the most common insulin delivery method.

The first thing to verify is whether your insulin concentration matches the syringe when choosing the appropriate syringe for the type of insulin you use.

The insulin concentration for which the syringe is intended is specified on the syringe and the container. Insulin concentration is expressed as U-100, U-200, or U-500 and is measured in Units/mL.

To avoid administering the incorrect amount of insulin, match your syringe to your insulin concentration.

The second thing you should do is pick the right syringe size for you. You should use a larger syringe if you use a lot of insulin at once to avoid dividing your dosages into smaller portions.

  • 0.3 mL insulin syringes are numbered at intervals of 1 unit and are used for dosages of less than 30 units of insulin.
  • 0.5 mL insulin syringes are numbered at 1-unit intervals and are used for dosages of 30 to 50 units of insulin.
  • 1.0 mL insulin syringes are numbered at intervals of 2 units and used for dosages greater than 50 units of insulin.

Finally, think about the needle length and size best for you. Similar to pen needles, smaller needle diameters are typically advised. The shortest syringe needle length accessible is 6 mm (15/64") x 31G, while insulin syringes with needles as long as 12.7 mm (1/2") long are also available.

Injection Tips

While it's crucial to select a needle length or syringe that works for you, you'll also want to keep in mind the following to make injections more bearable and reduce the possibility of pain or leakage:

  • Replace the needle every time.
  • Rotate your injection sites after selecting the best location.
  • Do not insert the needle forcefully.
  • Hold it for 5-8 seconds to lessen the chance of leakage.
  • Always use alcoholic wipes to disinfect.

Frequently Asked Questions

How often do I need to change my needle? 

Pen and insulin syringe needles are single-use items that should only be used once because they lose their sterility and sharpness.

What are the four types of insulin?

Short-acting, intermediate-acting, rapid-acting, and long-acting insulin.

Do smaller needles hurt less?

Needles with smaller diameters might cause less pain, which improves patient acceptance.


Injecting insulin is crucial for the health maintenance of diabetics. Many people take their insulin with a needle and syringe since it's convenient and affordable.

The syringe and needle size can significantly impact a person's comfort level and blood glucose levels if they regularly inject insulin. People can speak with their diabetes care team if they have questions or concerns about needle size and technique.


At Diabetic Me, we are committed to delivering information that is precise, accurate, and pertinent. Our articles are supported by verified data from research papers, prestigious organizations, academic institutions, and medical associations to guarantee the integrity and relevance of the information we provide. You can learn more about our process and team on the about us page.

  1. CDC 4 Ways To Take Insulin
  2. Wikipedia Subcutaneous injection
  3. New injection recommendations for patients with diabetes
  4. Cleveland Clinic Intramuscular Injection

About the Author

Ely Fornoville

Hi, I'm Ely Fornoville, and I am the founder of Diabetic Me. Being a type 1 diabetic since 1996, I developed a passion to help people learn more about diabetes. I write about diabetes and share stories from other diabetics around the world. I currently use a Medtronic Guardian 4 CGM and a MiniMed 780G insulin pump with Humalog insulin.

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