Three numbers decide every injection: how much peptide is in the vial, how much bacteriostatic water you add, and what the syringe is graduated in. Get those right once and the rest is arithmetic.
Concentration (mg/mL) = vial strength (mg) / diluent volume (mL).
Volume (mL) = dose (mg) / concentration (mg/mL). A 0.25 mg dose from a 2.5 mg/mL vial is 0.1 mL.
A U-100 syringe is graduated so 100 units = 1 mL, so units = mL x 100. The 0.1 mL above is 10 units on the barrel.
| Concentration | 0.25 mg | 0.5 mg | 1.0 mg |
|---|---|---|---|
| 2.5 mg/mL | 10 units | 20 units | 40 units |
| 5.0 mg/mL | 5 units | 10 units | 20 units |
| 10 mg/mL | 2.5 units | 5 units | 10 units |
Doses = vial strength (mg) / dose (mg). A 10 mg vial at 2.5 mg per week is four weeks, whatever the dilution: adding more water changes the volume you draw, never the number of doses.
The fields worth recording per injection are date, compound, dose in mg, volume drawn, injection site, and vial open date. That is enough to reconstruct titration history and to spot when a vial is past its useful window. I keep mine in the Peptide Tracker & Calculator, which does the mg-to-units step above and tracks remaining doses per vial; the same dose calculator is what produced the table on this page.
Reconstitution notes here are arithmetic, not medical advice. Dosing decisions belong with a clinician.