One of the most common points of confusion with peptides is translating a dose in micrograms (mcg) into the unit markings on an insulin syringe. The syringe does not know what is inside it — it only measures volume. You need to bridge the gap between your dose in mcg and the volume that contains that dose.
Understanding Insulin Syringe Units
A standard U-100 insulin syringe is calibrated so that:
- 100 units = 1mL
- 50 units = 0.5mL
- 10 units = 0.1mL
The "units" on an insulin syringe are a measurement of volume, not a measurement of dose. They were designed for insulin, where 100 units of insulin equals 1mL. When used for peptides, we repurpose these volume markings to measure our solution.
The Conversion Process
To convert mcg to syringe units, you need one piece of information: your solution concentration in mcg/mL.
Formula
Example: 100mcg dose
Say you have a 5mg peptide vial reconstituted with 2mL of bacteriostatic water:
- Concentration = 5,000mcg / 2mL = 2,500mcg per mL
- For 100mcg: (100 / 2,500) x 100 = 4 units
Example: 250mcg dose
Same vial (2,500mcg/mL):
- For 250mcg: (250 / 2,500) x 100 = 10 units
Example: 500mcg dose
Same vial (2,500mcg/mL):
- For 500mcg: (500 / 2,500) x 100 = 20 units
Quick MCG-to-Units Reference
For a 5mg vial reconstituted with 2mL water (2,500 mcg/mL):
| Desired Dose | Syringe Units | Volume (mL) |
|---|---|---|
| 50 mcg | 2 units | 0.02 mL |
| 100 mcg | 4 units | 0.04 mL |
| 200 mcg | 8 units | 0.08 mL |
| 250 mcg | 10 units | 0.10 mL |
| 500 mcg | 20 units | 0.20 mL |
| 1,000 mcg (1mg) | 40 units | 0.40 mL |
Tips for Accurate Measurement
- Use the correct syringe size. For doses under 10 units, a 0.3mL (30 unit) syringe gives finer graduation marks and better accuracy than a 1mL syringe
- Read at the flat edge of the plunger. The rubber stopper has a dome shape — read the measurement at the flat top edge closest to the needle, not the curved bottom
- Remove air bubbles. Tap the syringe with the needle pointing up and push air out before measuring. Air displaces liquid and throws off your dose
- Add more water during reconstitution if your doses keep landing between unit lines. More water = more units per dose = easier to measure
Skip the math entirely with our MCG to units converter — enter your concentration and desired dose, and it tells you exactly what to draw.