Choosing the Best Syringe and Needle Size for an Injection

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If you are prescribed a self-administered drug that you will need to regularly take at home, such as fertility drugs or hormones, vitamin B12 shotsinsulinepinephrine, or cancer medications, you will have several important responsibilities.

You will need to learn how to safely inject yourself with your medication as well as purchase the needles and syringes (clear tubes that hold the drug) required to administer your shots.

Choosing the right size needle and syringe is necessary to get the correct dose of medicine, inject it properly, and minimize pain. To make it easier, these items are sold separately and designed to attach securely.

Your healthcare provider or a nurse will show you how to administer your injections at home, including which syringes and needles to use. However, it helps to be familiar with the basic principles of needle and syringe sizing so you can avoid errors when it's time to replace them.

The 3 Basic Principles of Needle and Syringe Sizing
Verywell / Gary Ferster 

Syringe Sizes

Syringes are labeled based on how much liquid they can hold. There are two ways syringe capacity can be measured.

Syringe Capacity Measurement

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

Whichever measurement is used, 1 cc is equal to 1 mL.

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

For example, if you're supposed to give yourself 3 cc of a drug, you would want to use a syringe that holds precisely 3 cc (or just a little more). If you use a syringe that contains only 2 cc, you would have to inject yourself more than once (which would be unnecessarily painful).

On the other hand, if you use a syringe that holds 15 cc, it will be harder to see the cc markings and measure 3 cc accurately. 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.

Determining Needle Size

  • The first number in front of the letter G indicates the gauge of the needle. The higher this number is, the thinner the needle.
  • The second number indicates the length of the needle in inches.

For example, a 22 G 1/2 needle has a gauge of 22 and a length of half an inch.

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 as opposed to 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, a wide, low-gauge needle will deliver the injection faster than a thin, high-gauge needle.

Needle Length

As far as the needle length, the best choice will depend on a person's size (a small child would need a shorter needle than an adult) as well as where the needle will be inserted. As well, some medications can be absorbed superficially (directly underneath the skin) while others need to be injected into the muscle.

Subcutaneous injections go into the fatty tissue just below the skin. Since these are relatively shallow shots, the needle required is small and short—typically one-half to five-eighths of an inch long with a gauge of 25 to 30.

Intramuscular injections go directly into a muscle. Muscle is deeper than the subcutaneous layer of skin, so the needle used for intramuscular injections must be thicker and longer. 20 or 22 G needles that are an inch or an inch-and-a-half-long are usually best.

For these injections, you must consider the amount of body fat the needle has to go through. While a thin person might be able to use an inch-long needle, someone heavier might need a needle that is an inch-and-a-half-long.

A Word From Verywell

If you are prescribed a medication you'll need to regularly inject yourself at home, you'll need to know how to do so safely. You might have to learn how to correctly administer the medicine to yourself, or a family member may need to learn how to inject you. If you are caring for someone who needs injections at home, you may need to learn how to give them shots.

When you need to give yourself or someone else an injectable medication, don't hesitate to contact the healthcare provider who prescribed them if you have questions. Knowing the basics of needle size labeling will help you avoid making errors when injecting medication, as well as ensuring you replace your supplies correctly.

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8 Sources
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.
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