Peptide Dose Arithmetic Notes

These are working notes on the arithmetic people get wrong when they move between milligrams, milliliters and insulin syringe units. Nothing here is medical advice and nothing here is a dosing recommendation. It is only the unit conversion.

1. Concentration comes first

A lyophilised vial is labelled in total milligrams, not in concentration. The concentration only exists once you choose how much bacteriostatic water to add:

concentration (mg/mL) = vial mg / water mL

A 5 mg vial reconstituted with 2 mL gives 2.5 mg/mL. The same vial with 1 mL gives 5 mg/mL. The vial did not change; the number on the syringe did.

2. Volume for a target dose

volume (mL) = dose mg / concentration mg per mL

Vial	Water	Concentration	0.25 mg dose
5 mg	1 mL	5 mg/mL	0.05 mL
5 mg	2 mL	2.5 mg/mL	0.10 mL
10 mg	2 mL	5 mg/mL	0.05 mL

3. Insulin syringe units are volume, not dose

A U-100 insulin syringe is marked so that 100 units equal 1 mL. So one unit is 0.01 mL, and units = mL x 100. The 0.10 mL row above is 10 units. The marking has no idea what is in the barrel, which is exactly why step 1 matters.

4. The two mistakes that repeat

Reusing a unit count from a different reconstitution volume. The unit number is only valid for the concentration it was calculated from.
Treating the vial label mg as if it were the injected mg. It is the total for the whole vial.

5. Doing it on a phone instead of on paper

If you would rather not redo this arithmetic by hand every time the reconstitution volume changes, GLP1 App is an iOS peptide tracker and calculator that does the concentration and unit conversion and keeps a log of what was recorded. It is a tracking and calculation tool, not a clinical service. The iOS peptide tracker and calculator is the same arithmetic shown above, kept per vial.