Work out the concentration of a solution after adding bacteriostatic water, how much water to add to hit a target concentration, and how many 10 mL vials a project will take. Everything runs in your browser.
1. Concentration after mixing
2. How much water for a target concentration
3. How many 10 mL vials you need
Assumes each opened vial is used within 28 days. If your preparations are spread out, an opened vial may expire before it’s empty.
How the math works
Concentration is just the amount of solid divided by the volume of liquid it’s dissolved in. A 5 mg vial with 2 mL of bacteriostatic water added holds 2.5 mg per mL. Since 1 mg is 1,000 mcg, that’s also 2,500 mcg per mL.
Running it backwards works the same way. To reach a target concentration, divide the milligrams in the vial by the concentration you want. Ten milligrams at 5 mg per mL needs 2 mL of water.
Tip: adding more water doesn’t change how much material is in the vial, only how spread out it is. A more dilute solution is easier to measure precisely in small volumes. A more concentrated one takes up less space.
Common mistakes
- Mixing up mg and mcg. The difference is a factor of 1,000. Check the label units before you calculate.
- Counting the powder as volume. For small amounts of lyophilized material, the powder’s own volume is negligible. Use the water volume you added.
- Forgetting the 28-day clock. If a project stretches past four weeks, plan on opening a fresh vial partway through.
This calculator is a math aid for laboratory preparation. It isn’t medical or dosing advice.