The most useful habit in concentration math is simple: write a unit after every number. A result of “10” is incomplete until you know what the 10 represents.
Mass: milligrams and micrograms
Both units describe how much material is present. One milligram equals 1,000 micrograms. To convert mg to mcg, multiply by 1,000. To convert mcg to mg, divide by 1,000.
| Milligrams | Micrograms |
|---|---|
| 0.1 mg | 100 mcg |
| 0.5 mg | 500 mcg |
| 1 mg | 1,000 mcg |
| 2 mg | 2,000 mcg |
Unit-conversion examples only; these are not recommended doses.
Volume: milliliters
Milliliters describe the space occupied by a liquid. You cannot convert a mass directly to a liquid volume without knowing the concentration.
Volume = mass ÷ concentration
Concentration: two units together
The expression “mg/mL” answers a question: how many milligrams are represented by one milliliter? It connects mass and volume, making the conversion possible.
U-100 markings are not peptide IU
On a U-100 volume scale, 100 markings correspond to 1 mL, 50 to 0.5 mL, and 10 to 0.1 mL. These relationships describe a scale. They do not tell you how much peptide is present without a concentration.
International Units (IU) refer to biological activity defined for a particular substance. There is no universal IU-to-mg conversion across compounds. Do not substitute syringe markings for IU.
Check before trusting a result
- Do the starting mass and target mass use the same unit?
- Is the volume the documented final solution volume?
- Are you using the correct scale for the actual equipment?
- Is the calculated amount within the stated container and equipment limits?
- Have you kept the original inputs with the result?
A mathematically exact answer can still be physically unmeasurable or clinically inappropriate. Avoid treating extra decimal places as proof of accuracy.
FDA has documented medication errors linked to confusion between mass, volume and syringe units.
FDA: dosing errors associated with compounded injectable semaglutide ↗