How the peptide calculator works
The calculator uses the amount in milligrams and the entered dilution volume in millilitres to calculate mg per mL. It assumes the entered volume is the resulting solution volume. From that concentration, it converts a known dose to a volume and to U-100 syringe markings. It does not select a dose, confirm a product's suitability, or provide preparation instructions.
The formula
| Quantity | Formula |
|---|---|
| Concentration (mg/mL) | peptide mg / water mL |
| Micrograms per unit | concentration x 1000 / 100 = concentration x 10 |
| Units to draw | dose mcg / micrograms per unit |
| mL to draw | units / 100 |
| Doses per vial | vial mg x 1000 / dose mcg |
Worked example
A 5 mg vial with 2 mL of water: 5 / 2 = 2.5 mg/mL, which is 2,500 mcg per mL. One unit is 0.01 mL, so each unit carries 25 mcg. A 250 mcg dose is 250 / 25 = 10 units, or 0.1 mL. The vial holds 5,000 / 250 = 20 doses. Add 1 mL instead of 2 and the same dose becomes 5 units; add 4 mL and it becomes 20 units.
Insulin syringe sizes
| Syringe | Capacity in U-100 units |
|---|---|
| 0.3 mL | 30 units |
| 0.5 mL | 50 units |
| 1 mL | 100 units |
These capacities apply to U-100 markings. The spacing of individual marks varies by syringe, so check the actual device. For a fixed amount of peptide and a fixed dose, increasing the dilution volume increases the calculated mL and syringe units. The comparison table illustrates that relationship; ask your pharmacist to confirm the correct concentration and syringe rather than changing preparation details to match an example.
Common mistakes
Always include the unit: 2.5 mg is 2,500 mcg, while 250 mcg is 0.25 mg. Syringe units describe a volume on the specified device, not a fixed amount of peptide. A change in concentration changes the amount of peptide in the same volume. The FDA's report on compounded semaglutide dosing errors describes errors involving mg, mL, syringe units, and different concentrations, and advises patients to confirm measurement instructions with their health care provider or compounder.
Preparation and storage
Diluent choice, preparation, storage conditions, and the beyond-use date depend on the specific product. This arithmetic tool cannot establish them or replace instructions from your qualified prescriber or pharmacist. See our calculator methodology and limitations for how examples and estimates are presented.