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Basics & Technique

What needle size do I use?

Updated 2026-05-02

For subcutaneous (under-the-skin) injections, use a 29G, 30G, or 31G insulin syringe with an 8 mm (5/16 inch) needle. That is the standard, and it's what beginners should buy. Higher gauge numbers mean thinner needles. 31G is the thinnest of the three and hurts the least. 8 mm reaches the fat layer without going into muscle.

IfIf you are lean with very little subcutaneous fat
Thenthen use a 6 mm needle instead of 8 mm
IfIf you inject in the abdomen
Thenthen stay at least 2 inches from your belly button and rotate sites
IfIf you feel a lot of resistance going in
Thenthen check the needle - a bent or clogged one needs to be replaced
Key facts
  • Gauge options: 29G, 30G, 31G are all appropriate for subcutaneous peptide injection
  • Length: 8 mm (5/16 inch) for most adults; 6 mm acceptable for very lean individuals
  • Syringe sizes: 0.3 mL (30u) for small doses, 0.5 mL (50u) for medium, 1.0 mL (100u) for larger-volume compounded GLP-1s
  • Rotate sites (abdomen, thigh, back of upper arm) to prevent lipohypertrophy (fibrous lumps under the skin)
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