Syringe & Measurement Guide
How to read U-100, U-50, and U-20 insulin syringes. IU vs mg vs mcg vs syringe units fully explained — including worked examples to eliminate dosing confusion.
Unit confusion is the #1 source of peptide dosing errors. This guide explains the three measurement systems you'll encounter and how to convert between them.
The Three Measurement Systems
When working with research peptides, you'll encounter three completely different types of "units" that measure completely different things:
| Unit Type | Examples | What It Measures | Example Use |
|---|
| Weight units | mg, mcg | Mass of peptide | "Dose: 250 mcg BPC-157" |
| Volume units | mL, syringe units | Liquid volume | "Draw 15 units on syringe" |
| Potency units | IU | Biological activity | "2 IU of HGH" |
Weight Units: mg and mcg
1 mg (milligram) = 1,000 mcg (micrograms)
The peptide amount in a vial is given in weight. The amount you're trying to dose is also in weight. The most critical rule: confusing mg and mcg produces a 1,000-fold error. Always verify which unit a protocol uses.
- BPC-157: typically dosed in mcg (e.g., 250 mcg/day)
- Semaglutide: typically dosed in mg (e.g., 0.25 mg/week)
- Retatrutide: dosed in mg (e.g., 2–12 mg/week)
- Ipamorelin: dosed in mcg (e.g., 200 mcg/dose)
The U-100 Insulin Syringe
The most common syringe for peptide research. "U-100" means 100 units per mL:
- 100 syringe units = 1.0 mL
- 1 syringe unit = 0.01 mL
- A full U-100 syringe (1 mL) holds 100 units of liquid
Converting Dose to Syringe Units (Complete Example)
Peptide: Ipamorelin 10 mg vial
BAC water: 3.0 mL added
Concentration: 10 mg ÷ 3.0 mL = 3.33 mg/mL
Target dose: 200 mcg = 0.2 mg
Volume needed: 0.2 mg ÷ 3.33 mg/mL = 0.060 mL
U-100 syringe units: 0.060 mL × 100 = 6 units
Choosing the Right Syringe Type
| Syringe Type | Capacity | Markings | Best For |
|---|
| U-100, 1 mL | 100 units = 1.0 mL | 1 unit = 0.01 mL | Most peptide doses; volumes 10–100 units |
| U-100, 0.5 mL | 50 units = 0.5 mL | More spread out | Small doses; easier reading at 5–50 units |
| U-100, 0.3 mL | 30 units = 0.3 mL | Maximum readability | Very small doses; <30 units |
Key rule: If your dose requires fewer than 10 syringe units on a standard 100-unit syringe, use a smaller syringe (30- or 50-unit capacity) for much better accuracy. Small volumes on large syringes are difficult to measure precisely.
IU (International Units) — HGH and HCG
IU measure biological potency, not volume. They are defined differently for each substance:
- HGH: 1 mg ≈ 3 IU (or 1 IU ≈ 0.333 mg). A "10 IU vial" contains approximately 3.33 mg of HGH.
- HCG: Vials come in IU (e.g., 5,000 IU). IU are defined by bioassay, not by mass.
HCG Conversion Example — 5000 IU Vial
Vial: HCG 5,000 IU
BAC water added: 5.0 mL
Concentration: 5,000 IU ÷ 5.0 mL = 1,000 IU/mL
Target dose: 500 IU
Volume needed: 500 IU ÷ 1,000 IU/mL = 0.50 mL
U-100 syringe units: 0.50 × 100 = 50 units
Note: these "units" are U-100 syringe volume units — not IU!
Reading the Syringe Scale
Hold the syringe at eye level with the scale vertical. The dose is read at the bottom of the rubber plunger tip (the flat edge that faces toward the needle). The markings represent the volume below that line.
- Each major line = 10 units (0.10 mL)
- Each minor line = 2 units (0.02 mL) on most U-100 syringes
- Half-unit precision requires a smaller syringe (0.3 mL capacity)