Methodology

How DoseMath calculates your draw

Every figure DoseMath shows is plain arithmetic. Here is each formula and a full worked example, so you can check the tool by hand instead of trusting it.

The inputs

You give DoseMath four things: the mass of peptide in the vial (milligrams), the amount of bacteriostatic water you add (millilitres), your dose per injection (micrograms or milligrams), and which syringe you draw with. Everything below follows from those.

1. Concentration

Reconstituting dissolves the peptide evenly into the water, so the concentration is simply mass over volume.

concentration (mg/mL) = peptide mass (mg) ÷ water (mL)
concentration (mcg/mL) = concentration (mg/mL) × 1000 (1 mg = 1000 mcg)

2. Injection volume

The volume you need is your dose divided by the concentration, with both in the same unit of mass.

injection volume (mL) = dose ÷ concentration

3. Units to draw

Insulin syringes are marked in units, not millilitres. A U-100 syringe has 100 units per millilitre; a U-40 syringe has 40. Multiply the volume by that number to get the mark to draw to.

units to draw = injection volume (mL) × units per mL
U-100: × 100 | U-40: × 40

4. Micrograms per unit

Useful for sanity-checking a dose: how much peptide sits in one syringe unit.

mcg per unit = concentration (mcg/mL) ÷ units per mL

5. Doses per vial

How many injections the vial holds at your chosen dose.

doses per vial = total peptide ÷ dose per injection

Worked example

A 5 mg vial, 2 mL of bacteriostatic water, a 250 mcg dose, drawn on a U-100 syringe:

concentration = 5 mg ÷ 2 mL = 2.5 mg/mL = 2500 mcg/mL
volume = 250 mcg ÷ 2500 mcg/mL = 0.10 mL
units to draw = 0.10 mL × 100 = 10 units
mcg per unit = 2500 ÷ 100 = 25 mcg
doses per vial = 5000 mcg ÷ 250 mcg = 20

So you would draw to the 10-unit mark, and the 5 mg vial gives 20 doses. These are the same numbers the calculator shows for those inputs.

Built-in safeguards

Arithmetic is easy to get right and easy to mis-enter, so DoseMath checks the result against the real syringe:

Snap to mark. It confirms when your draw lands exactly on a graduation, and warns when it falls between marks where it is hard to measure.
Over capacity. It flags a draw that exceeds the selected syringe's volume.
Very small draw. It warns on draws under about two units, where a small error is a large percentage.
1000× guard. Because doses are entered in both mcg and mg, it catches the common thousand-fold mix-up between the two.

Verify it yourself

Nothing here is proprietary. The formulas are standard, and the point of showing them is that the methodology is the proof: run your own numbers and you should get what DoseMath gets. If you don't, that is a bug worth reporting, and it will appear in the changelog.

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