1. What an insulin syringe is
An insulin syringe is a small, single-use syringe purpose-built for subcutaneous injections of insulin. They were designed to measure insulin in units — a concentration-independent number — rather than millilitres.
Peptide researchers adopted insulin syringes because the needles are extremely fine (28–31 gauge), the volumes are small (0.3–1.0 mL), and the U-100 unit scale makes dose calculation consistent regardless of how you reconstitute.
Every standard insulin syringe sold today is U-100, meaning it is calibrated for insulin at a concentration of 100 units per mL. That one fact is the foundation for everything else on this page.
2. The 0–100 unit scale
Look at any 1 mL insulin syringe and you will see numbers running from 0 at the plunger to 100 at the needle end. Those numbers are units, not mL.
Standard U-100 insulin syringe (1 mL)
The scale works like this:
- Large lines (every 10 units) — these are the bold tick marks labelled 10, 20, 30 … 90, 100.
- Small lines — the unlabelled marks between each large line. On a 0.5 mL syringe each small line is 1 unit. On a 1.0 mL syringe, each small line is also 1 unit (sometimes 2 — check your brand).
3. The math behind the markings
The single most important fact: 100 units = 1 mL. Full stop. This is true for every U-100 syringe ever made.
Core conversions
100 units = 1 mL
10 units = 0.1 mL
1 unit = 0.01 mL
So if a calculation tells you to draw 0.25 mL, that is exactly:
0.25 × 100 = 25 units
Why units instead of mL?
Insulin syringes were designed for insulin, which is always sold at 100 units/mL. Because concentration is fixed, the unit number directly equals the insulin dose — no arithmetic needed for diabetics. Peptide researchers inherited the syringe and the unit scale, so we have to do a small conversion step.
That conversion is: concentration × volume = dose. The reconstitution calculator on this site does it for you, but understanding the maths means you can double-check any result in your head.
The full peptide dose formula
Step by step
Step 1 — concentration:
vial mg × 1000 ÷ BAC water mL = mcg per mL
Step 2 — volume per dose:
dose mcg ÷ mcg per mL = mL to draw
Step 3 — convert to units:
mL to draw × 100 = units to draw
Example: 5 mg vial + 2 mL BAC water + 250 mcg dose
5 × 1000 ÷ 2 = 2500 mcg/mL → 250 ÷ 2500 = 0.1 mL → 0.1 × 100 = 10 units
4. Syringe sizes: 0.3, 0.5, and 1.0 mL
U-100 insulin syringes come in three barrel sizes. The unit scale always runs 0–100, but the physical length of the barrel changes:
| Size | Max volume | Smallest increment | Best for |
|---|---|---|---|
| 0.3 mL (30 units) | 30 units | 1 unit | Very small doses (<30 units); easiest to read accurately |
| 0.5 mL (50 units) | 50 units | 1 unit | Most peptide protocols — the standard choice |
| 1.0 mL (100 units) | 100 units | 1–2 units | Larger doses or higher-volume draws |
5. Gauge and needle length
Gauge is the diameter of the needle — higher gauge = thinner needle. For subcutaneous peptide injections, thinner is better: less pain, smaller puncture, no meaningful difference in delivery speed at these volumes.
| Gauge | Needle length | Notes |
|---|---|---|
| 28G | 8 mm (5/16“) | Good for most users |
| 29G ✓ | 8 mm (5/16“) | Most common — the standard choice |
| 30G | 8 mm (5/16“) | Very fine; slightly slower draw but minimal pain |
| 31G | 6 mm (1/4“) | Ultra-fine; suitable for very lean individuals |
For subcutaneous injections, needle length matters less than gauge. 8 mm is fine for most injection sites (abdomen, outer thigh, upper arm fat). If you are very lean, 6 mm reduces the chance of accidental intramuscular delivery.
6. Converting mcg → units
Peptide doses are specified in micrograms (mcg). Your syringe is marked in units. To convert, you need to know the concentration of your reconstituted vial. The formula is always the same:
Interactive: mcg → units converter
Draw to:
10.0 units
Concentration: 2500 mcg/mL
= 25.0 mcg per unit
Standard U-100 insulin syringe (1 mL)
The calculator above mirrors the full reconstitution calculator. Use it to verify your maths before every new vial.
7. Reading the scale in practice
Once you know how many units to draw, reading the syringe is straightforward:
- Hold the syringe horizontal at eye level. Looking down at the syringe from above introduces parallax error — the rubber stopper will appear higher than it actually is.
- Read from the top (flat) edge of the rubber stopper, not the bottom dome edge. The flat edge is the measurement line.
- Count the lines from zero. Each small line is 1 unit. Each large labelled line is 10 units. Draw up slowly, past your target, then push back down to the exact unit.
- Remove air bubbles before reading. Tap the barrel and push the plunger gently to expel air; then re-draw to your target unit.
Quick-reference card
10 units
0.1 mL
20 units
0.2 mL
50 units
0.5 mL
100 units
1.0 mL
8. Common mistakes
✗ Confusing units with mL
Drawing to 0.25 on the mL scale of a regular syringe is not the same as drawing to 25 on an insulin syringe. Never use a standard 3 mL syringe for peptide dose drawing — always use a U-100 insulin syringe.
✗ Using the wrong BAC water volume in your calculation
If you add 2 mL of water but calculate with 1 mL, your dose will be half of what you think. Always measure the actual water volume you add, and enter that number into the calculator.
✗ Reading the syringe from the wrong edge
Read from the flat top of the rubber stopper, not the curved bottom dome. The dome can add 1–2 units of apparent reading depending on the stopper geometry.
✗ Buying the wrong syringe size
A 0.3 mL syringe only goes to 30 units. If your dose is 40 units you cannot draw it — you would need a 0.5 mL or 1.0 mL syringe. Calculate your likely dose before buying syringes.
✗ Skipping the air bubble check
A 5-unit air bubble at the top of the barrel means you drew 5 fewer units than you think. Always flick the barrel to bring bubbles to the top and push them out before recording or injecting.
Ready to calculate your dose?
Enter your vial size and BAC water volume. The calculator draws the syringe for you.