Practical guide
Peptide Dosing Units Explained (mcg vs mg)
Peptide doses are typically expressed in micrograms — this reference explains the relationship between mcg and mg, how to convert, and how to apply units to real peptide calculations.
The Two Units You Need to Know
Milligram (mg)
One thousandth of a gram. Vial sizes are labelled in milligrams — for example, "5 mg vial" or "10 mg vial". This describes the quantity of peptide powder contained in the vial before reconstitution.
Microgram (mcg or μg)
One millionth of a gram — one thousandth of a milligram. Individual doses are expressed in micrograms because peptides exert biological effects at very small quantities. A dose of "250 mcg" is equivalent to 0.25 mg or 0.00025 g.
Why Peptides Are Dosed in Micrograms
Peptides are biologically potent at very small quantities due to their receptor binding efficiency. Using micrograms as the unit keeps dose figures in a manageable numerical range for calculation. Writing "250 mcg" is clearer and less error-prone than "0.25 mg" or "0.00025 g" when working out small injection volumes.
The exception is compounds where research has investigated higher quantities — some GLP-1 receptor agonist peptides, for instance, have commonly reported doses in the milligram range. In those cases the dose may be expressed as "2 mg" rather than "2,000 mcg". Both are equally correct; the key is being consistent in your calculation chain.
Converting Between Units
| mg value | Equivalent in mcg |
|---|---|
| 0.1 mg | 100 mcg |
| 0.25 mg | 250 mcg |
| 0.5 mg | 500 mcg |
| 1 mg | 1,000 mcg |
| 2 mg | 2,000 mcg |
| 5 mg (full vial) | 5,000 mcg |
| 10 mg (full vial) | 10,000 mcg |
From Dose to Syringe Volume: The Full Chain
This five-step sequence is the complete calculation you need before drawing from a reconstituted vial.
Worked Example 1: BPC-157, 250 mcg
BPC-157 — 5 mg vial, 250 mcg commonly reported dose
- Vial: 5 mg BPC-157
- BAC water added: 2 ml
- Concentration: (5 × 1,000) ÷ 2 = 2,500 mcg/ml
- Volume for 250 mcg: 250 ÷ 2,500 = 0.10 ml
- U-100 syringe units: 0.10 × 100 = 10 units
Worked Example 2: Retatrutide, 2 mg
Retatrutide — 10 mg vial, 2 mg commonly reported dose
- Vial: 10 mg Retatrutide
- BAC water added: 2 ml
- Concentration: (10 × 1,000) ÷ 2 = 5,000 mcg/ml
- Dose: 2 mg = 2,000 mcg
- Volume for 2,000 mcg: 2,000 ÷ 5,000 = 0.40 ml
- U-100 syringe units: 0.40 × 100 = 40 units
Quick Reference: Common Dose Conversions
| Dose (mcg) | Dose (mg) | Notes |
|---|---|---|
| 100 mcg | 0.1 mg | Common low-dose range |
| 200 mcg | 0.2 mg | Common BPC-157 / Semax range |
| 250 mcg | 0.25 mg | Common mid-range dose |
| 500 mcg | 0.5 mg | Common upper range |
| 1,000 mcg | 1 mg | Threshold between mcg and mg labelling conventions |
| 2,000 mcg | 2 mg | Common GLP-1 agonist research range |
| 5,000 mcg | 5 mg | Full standard vial equivalent |
Common Mistakes
- Confusing mg and mcg — drawing a "2 mg" volume when the figure given was "2 mcg" is a 1,000× error
- Forgetting to convert the vial label from mg to mcg before calculating concentration (e.g. entering "5" instead of "5,000" in the concentration formula)
- Rounding concentration to a whole number and introducing error — use the exact figure throughout the chain
- Using the wrong syringe calibration (U-40 instead of U-100) — the unit count at the syringe changes even when the volume calculation is correct
Key Takeaways
- 1 mg = 1,000 mcg — vials are labelled in mg, individual doses are expressed in mcg
- Concentration (mcg/ml) = (vial mg × 1,000) ÷ volume of BAC water added (ml)
- Dose volume (ml) = desired dose in mcg ÷ concentration in mcg/ml
- U-100 syringe units = dose volume in ml × 100
- A mg/mcg confusion error produces a 1,000× discrepancy — always check units at each step
- Use the interactive peptide calculator to verify your calculation chain and avoid manual errors