Final answer:
The preferred needle length for an SQ injection is typically 1/2 inch to 5/8 inch, but may vary based on patient size and medication type.
Step-by-step explanation:
The preferred length of the needle for an SQ (subcutaneous) injection is 1/2 inch to 5/8 inch for an average-sized adult. For an SQ injection, a 25 to 30 gauge needle is also commonly used. The length can vary depending on the patient's body mass and the site of the injection.
For obese patients, a longer needle may be necessary, such as a 1 inch needle, to ensure that the medication is injected into the subcutaneous tissue rather than into the muscle or dermis. It's also important to consider the viscosity of the medication and the angle at which the injection will be administered.