Describe the proper needle gauge and typical volume for intramuscular injections in adults.

• A. 18–20 gauge; 1.5 inches; up to 5 mL
• B. 22–25 gauge; 1–1.5 inches; up to 2 mL
• C. 26–28 gauge; 1 inch; up to 0.5 mL
• D. 20–22 gauge; 2 inches; up to 3 mL

Answer: (B)

When giving intramuscular injections to adults, the goal is to reach the muscle cleanly while minimizing tissue trauma and pain. A needle in the 22–25 gauge range provides a good balance: it’s not so large that it causes unnecessary tissue damage, but not so fine that viscous medications flow poorly. Using too large a bore, like 18–20 gauge, would be more traumatic for most IM meds, while too-small a bore (26–28 gauge) can impede flow and be uncomfortable for injections that aren’t very thin.

The length should be enough to reach the muscle through the subcutaneous layer without going so deep as to risk bone or other structures. For most adults, 1 to 1.5 inches hits the muscle reliably, while longer needles (like 2 inches) are reserved for individuals with greater body fat or specific injection sites, and shorter needles (1 inch) may not reach muscle in some patients.

Volume matters because placing too much medication in a single site can cause distension, pain, and tissue damage. About 2 mL is a common upper limit for a single IM injection in adults; larger volumes are typically split or given in larger muscles such as the gluteal area.

So, the best match is a gauge of 22–25, a length of 1–1.5 inches, and up to 2 mL per injection.