Choosing the Right Needle For Your Injections

Needles and syringes come in different sizes, and some are better suited for certain uses than others. Having the correct needle and syringe for you helps ensure you get the correct amount of your medication. It may also make injections easier and less painful.

The right needle size for your injections depends on how much medication you need, your body size, and whether the drug has to go into a muscle or under the skin. Your syringe also has to be big enough to hold the right dose, but not so big that it makes measuring small amounts difficult.

This article explains how needles and syringes are sized. It also provides some helpful tips for choosing the right size for the type of injection you need to give yourself.

Syringe Sizes

Syringes are labeled based on how much medication they can hold.

Measurements on syringes:

• Milliliters (mL) for liquid volume
• Cubic centimeters (cc) for the volume of solids

1 cc is equal to 1 mL.

If you are injecting your medication at home, you need to choose a syringe that will hold the dose you've been prescribed.

For example, if you're supposed to give yourself 3 ccs of a drug, you need a syringe that holds exactly 3 ccs or just a little more. If you use a syringe that can only hold 2 ccs, you would have to inject yourself more than once (using a brand new syringe and needle each time).

On the other hand, if you use a syringe that holds 15 ccs, it will be harder to see the cc markings. You could easily end up giving yourself too little or too much medication.

Needle Sizes

Needles are labeled differently than syringes. The packaging will have a number, then a "G," and then another number.

• The first number in front of the letter G indicates the gauge of the needle. The higher the number, the thinner the needle. So an 18-gauge needle has a smaller diameter than one that's 16 gauge, for example.
• The second number indicates the length of the needle in inches.

Here's an example: A 22 G 1/2 needle has a gauge of 22 and a length of 1 1/2 inches.

Needle Gauge

If you need to inject yourself with a small amount of medication, it will usually be less painful to use a thin, high-gauge needle rather than a wider, lower-gauge needle.

For larger amounts of medicine, a wider needle with a lower gauge is often a better choice. While it might hurt more, it will deliver the drug faster than a thin, high-gauge needle.

Needle Length

The best choice for needle length depends on a person's size—for example, a small child would need a shorter needle than an adult. Where the needle will be inserted also matters.

Some medications can be absorbed just under the skin, while others need to be injected into the muscle:

• Subcutaneous injectionsgo into the fatty tissue just below the skin. These shots are fairly shallow. The needle required is small and short (typically 1/2 to 5/8 of an inch long) with a gauge of 25 to 30.
• Intramuscular injectionsgo directly into a muscle. Since muscle is deeper than the skin, the needle used for these shots has to be thicker and longer. Needles with a gauge of 20 or 22 G and a length of 1 or 1 1/2 inches are usually best for intramuscular injections.

You also need to think about how much body fat the needle will have to go through. A thinner person might be able to use a 1-inch long needle but someone heavier might need a needle that is 1 1/2 inches long.

Summary

Syringes can hold liquids or solids. You'll see milliliters (mL) marked on the tube for measuring liquids. You'll see cubic centimeters (ccs) for measuring solids. It's best to choose a syringe that holds the exact dose you need.

Needles are measured differently. The first number on a needle label is its gauge—how thick the needle is. Higher numbers mean thinner needles. The second number on the label is how long the needle is.

You'll need a longer needle if the medication is supposed to go into a muscle. You'll also need a longer needle for larger adults.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

1. McGill University Office for Science and Society. Does size matter when it comes to needles?
2. American Diabetes Association. Get a handle on diabetes medication.
3. Beirne PV, Hennessy S, Cadogan SL, Shiely F, Fitzgerald T, MacLeod F. Needle size for vaccination procedures in children and adolescents. Cochrane Database Syst Rev. 2018;8(8):CD010720. doi:10.1002/14651858.CD010720.pub3
4. Hamborsky J, Kroger A, Wolfe S, eds. Centers for Disease Control and Prevention. Epidemiology and prevention of vaccine-preventable diseases. Chapter 6: Vaccine administration. 13th edition. Washington, DC: Public Health Foundation
5. Salari M, Estaji Z, Akrami R, Rad M. Comparison of skin traction, pressure, and rapid muscle release with conventional method on intramuscular injection pain: A randomized clinical trial. J Educ Health Promot. 2018;7:172. doi:10.4103/jehp.jehp_216_18
6. Centers for Disease Control and Prevention. Vaccine recommendations and guidelines of the ACIP: Vaccine administration.

• Doyle GR, McCutcheon JA. (2015). . Chapter 7.3: Intradermal and subcutaneous injections. In: Clinical Procedures for Safer Patient Care. Victoria, BC: BCcampus
• Doyle GR, McCutcheon JA. Chapter 7.4: Intramuscular injections. In: Clinical Procedures for Safer Patient Care. Victoria, BC: BCcampus

By Nicole Galan, RN
Nicole Galan, RN, is a registered nurse and the author of "The Everything Fertility Book."

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