The needle and syringe matter as much as the dose. This explains the sizes, what "gauge" and "length" mean, which needles to use for mixing vs injecting, how to read the box, and how to dispose of them safely. Recommended options are highlighted in green.
For peptides you'll use a U-100 insulin syringe: 100 units = 1 mL, so a 10-unit draw is 0.1 mL. Three common barrel sizes — same units scale, the bigger ones just hold more:
Rule of thumb: pick the smallest barrel that still holds your dose — it spreads the same units over more space, so tiny draws are easier to measure. The calculator tells you the exact unit line.
🪡 What is "gauge"? (higher number = thinner needle)
Gauge (written like 31G) is the needle's thickness — backwards from what you'd expect: the higher the number, the THINNER the needle. Thinner hurts less. Here they are thinnest → thickest:
For injecting, stay in the 29G–31G range — 31G is the sweet spot (least pain). Don't inject with a 27G; it's noticeably thicker and hurts.
📐 Needle length (shorter is right for subcutaneous)
Peptides go subcutaneous — into the fat just under the skin — so you want a short needle. Drawn to scale:
5/16" = 8 mm is the standard short length and is ideal. Longer needles (1"+) are for intramuscular shots — not what you want here.
🧰 Mixing vs injecting — the two-box trick
The needle that's best for drawing water in (reconstituting) isn't the same as the one best for injecting. A clean setup is two separate boxes:
💉 Injection box (the important one)
0.3 mL · 31G · 5/16" (8 mm) fixed-needle insulin syringes. Tiny, thin, comfortable. This is what touches your body.
💧 Reconstitution box (optional, handy)
1 mL · 29G (or a 27–28G drawing needle). The bigger bore pulls bacteriostatic water in faster. You're not injecting with it, so a thicker needle is fine.
Don't mix them up. The point is to never inject with the bigger reconstitution needle. Keep the boxes apart and labeled. You don't have to own a separate mixing needle — the small injection syringe can draw water too, just slower.
🏷️ How to read the box
A syringe/needle box packs four numbers. Once you can read them, you know exactly what you're holding:
Volume / units — e.g. 1 mL (100 units) or 0.3 mL (30 units). The barrel size.
Gauge — e.g. 31G (thickness; higher = thinner).
Length — e.g. 5/16" (8 mm) or 1/2" (12.7 mm).
"Sterile · Single use" + a lot number and expiration date. Broken seal or expired = don't use.
A typical injection box reads: "31G × 5/16" — 0.3 mL — U-100 — Sterile, single use." That's the one you want for shots.
🧼 Safety & sterility (the short version)
One needle, one use. Needles dull instantly and aren't sterile after a single stick — never reuse.
Never share needles or vials with anyone (bloodborne-disease risk).
Swab the vial stopper before every draw, and swab your skin and let it dry before injecting.
Sterility is worth understanding properly — it's the difference between a clean shot and an infection. Read the full Sterility guide →
🗑️ Disposal — sharps & what to do without one
Best: a real sharps container (the small red bins, cheap online or at pharmacies). Drop the whole used syringe in; seal when ~3/4 full.
No sharps container? Use a rigid, puncture-proof, sealable plastic container — a heavy laundry-detergent or bleach bottle works. Cap on, tape it shut when full, label it "Sharps — do not recycle."
Where it goes: many pharmacies, clinics, and household-hazardous-waste / health-department sites take full sharps containers. Rules vary — search "sharps disposal near me."
Never: toss loose needles in the trash, recap by hand (use the one-handed "scoop" if you must), or bend/break them. Keep it all away from kids and pets.
🧮 Ready to dose?
The calculator tells you the exact water amount, the unit line to draw to, and which syringe fits.