Needles for Intramuscular Injections:

The syringe size for intramuscular injections ranges from 3 to 5 ml. The needle size and length vary according to factors such as the muscle to be used, the type of solution, how much adipose tissue is covering the muscle and the age of the patient.
The gauge (or opening diameter) of the needle varies from #18-#28. For intramuscular injections a longer needle is used to reach the muscle, commonly the length is 1-1 1/2 inches. The gauge for intramuscular injections is larger, from #20-#22. Some examples of situations that may alter the choice of needle length and gauge would be the slender adult or child that would require a shorter needle or a more viscous solution that would require a larger gauge.