Does size matter? Historically, a bigger needle gauge was considered better to prevent damage to red blood cells. However, our recent guidelines recommend using smaller gauge needles (2325 G) for all Understanding Needle Gauges and Injection Sites If youre still guessing needle sizes were not doing that in 2026 , Heres what you MUST know:, Smaller gauge number = BIGGER needle, 1820G = blood & trauma, 2123G = IM, 2527G = Self injecting vitamin B12. Quick and painless jabs after a B12 by Dr Caroline Palmer Medium