BAC Water Calculator
How much bacteriostatic water you add sets the concentration — and therefore how many syringe units a given amount takes. It never changes the amount of drug in the vial.
Want a specific number of units per draw? Use the reconstitution calculator, which solves for the water volume.
BAC water chart: mcg per syringe unit
Rows: vial size. Columns: water added. Cell: mcg in one U-100 unit (0.01 mL).
| Vial ↓ / Water → | 0.5 mL | 1 mL | 1.5 mL | 2 mL | 2.5 mL | 3 mL | 5 mL |
|---|---|---|---|---|---|---|---|
| 2 mg | 40 | 20 | 13.3 | 10 | 8 | 6.7 | 4 |
| 5 mg | 100 | 50 | 33.3 | 25 | 20 | 16.7 | 10 |
| 10 mg | 200 | 100 | 66.7 | 50 | 40 | 33.3 | 20 |
| 15 mg | 300 | 150 | 100 | 75 | 60 | 50 | 30 |
| 20 mg | 400 | 200 | 133.3 | 100 | 80 | 66.7 | 40 |
| 30 mg | 600 | 300 | 200 | 150 | 120 | 100 | 60 |
| 50 mg | 1,000 | 500 | 333.3 | 250 | 200 | 166.7 | 100 |
| 60 mg | 1,200 | 600 | 400 | 300 | 240 | 200 | 120 |
Why the water volume matters
- Too little water → very concentrated; small amounts become 1–3 units, where a one-line misread is a large percentage error.
- Too much water → larger volumes per draw, may exceed a 0.3 or 0.5 mL syringe.
- Pick a volume that makes your prescribed amount land on a readable, round mark — and confirm that choice with your pharmacist.
BAC water vs sterile water
Bacteriostatic water for injection contains 0.9% benzyl alcohol as a preservative so a vial can be entered multiple times; sterile water for injection contains no preservative. Use whichever diluent your product's labeling specifies.
FAQ
How much bacteriostatic water should I add?
The amount of diluent is a choice that sets the concentration; it does not change how much drug is in the vial. Use the volume specified by the product labeling or your pharmacist. This calculator shows what concentration and syringe readings result from any volume you choose.
How much BAC water for a 10 mg vial?
Any of several volumes can work mathematically: 1 mL gives 10 mg/mL (100 mcg per unit), 2 mL gives 5 mg/mL (50 mcg per unit), 3 mL gives about 3.33 mg/mL. Which one is appropriate is a labeling/pharmacist question.
Is bacteriostatic water the same as sterile water?
No. Bacteriostatic water contains 0.9% benzyl alcohol as a preservative, which allows multiple withdrawals; sterile water for injection has no preservative. Some medicines specify one or the other, and benzyl alcohol is not suitable for neonates.
Does adding more water reduce the dose?
No. More water lowers the concentration, so the same amount of drug takes up more syringe units.
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