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)