The gauge and length of the needle for an intramuscular (IM) injection depend on the patients age, weight, and the injection site. The deltoid muscle is most often used as the site for IM injections in adults, and the needle length is usually 1"–1½", 22–25 gauge. However, a longer or shorter needle may be needed depending on the patients weight. An alternate site for IM injection in adults is the anterolateral thigh muscle, and the needle length and gauge are the same as when the deltoid muscle is used. The following table outlines recommended needle gauges and lengths for IM injections based on CDC’s General Best Practice Guidelines for Immunization:

• Neonate, 28 days and younger: 22–25-gauge, 5/8 inch (16 mm), Vastus lateralis muscle of anterolateral thigh
• Infants, 1–12 months: 22–25-gauge, 1 inch (25 mm), Vastus lateralis muscle of anterolateral thigh
• Children and teens: 22–25-gauge, 1–1.5 inches (25–38 mm), Deltoid muscle of arm or anterolateral thigh muscle
• Adults: 22–25-gauge, 1–1.5 inches (25–38 mm), Deltoid muscle of arm or anterolateral thigh muscle

For subcutaneous injections, the needle gauge is usually 23–25, and the length is 5/8 inch (16 mm) for all ages. However, for areas of the body with smaller veins like the hands or feet, a higher gauge needle or butterfly needle is commonly used. It is important to note that clinical judgment should be used when selecting needles to administer injectable vaccines.