A BAC water calculator doesn't tell you what dose to take — it tells you what your concentration will be *after* you add the water, so you know how much liquid equals your desired dose.

You need two numbers from your vial:

1. Total peptide in the vial (mg)

2. How much bacteriostatic water you plan to add (mL)

Formula:

Concentration (mg/mL) = Peptide (mg) / BAC water (mL)

Then: mL for one dose = Desired dose (mg) / Concentration

Because most peptide doses are in mcg: 1 mg = 1000 mcg.

Example: 10 mg vial + 2 mL BAC water.

10 mg / 2 mL = 5 mg/mL = 5000 mcg/mL.

If you want 250 mcg: 250 / 5000 = 0.05 mL. On a U-100 syringe that's 5 units.

If you added 1 mL instead:

10 mg / 1 mL = 10 mg/mL = 10,000 mcg/mL.

250 mcg would be 0.025 mL = 2.5 units — much harder to measure accurately.

That's the tradeoff. More BAC water = lower concentration = larger, more forgiving volume. Less water = higher concentration = tiny volume, easier to make a mistake.

Use only bacteriostatic water (0.9% benzyl alcohol), wipe the stoppers, inject the water slowly down the vial wall, swirl gently. Refrigerate after mixing and check expiry. Confirm your math, storage, and dosing with your pharmacist or prescriber before use.