Three ways to use it
You know the concentration you want
Divide the vial's milligrams by the target mg/mL. A 10 mg vial at 5 mg/mL is 10 ÷ 5 = 2 mL of total solution; a 5 mg vial at 2.5 mg/mL is also 2 mL.
You want a dose to fill a set number of units
Some people find doses easier to measure when they land on a round number of units. Units ÷ 100 gives the mL, and the solution has to hold the dose in that volume. For 250 mcg to be 10 units from a 10 mg vial: 10 units is 0.1 mL, so the strength is 0.25 mg ÷ 0.1 mL = 2.5 mg/mL, and 10 ÷ 2.5 = 4 mL. Check the vial can hold that much.
You already added the water
Divide the vial's milligrams by the total volume. 10 mg in 3 mL is 3.333 mg/mL, so each 1 mg is 30 units. Then use the main calculator to turn any dose into units.
The formulas
total solution (mL) = vial (mg) ÷ target concentration (mg/mL) total solution (mL) = target units ÷ 100 × vial (mg) ÷ dose (mg) concentration (mg/mL) = vial (mg) ÷ total solution (mL)
Convert micrograms to milligrams first: 250 mcg is 0.25 mg. On a U-100 syringe 100 units is 1 mL, whatever the barrel size.
What the volume changes, and what it doesn't
The liquid only spreads the same amount of peptide over more or less volume. It doesn't change how much is in the vial or how much a dose contains. What it does change:
- Readability. A weaker solution puts small doses on more syringe lines, which can be easier to measure.
- Volume per dose. A weaker solution means more liquid in every dose, and large doses may not fit in one syringe.
- Room in the vial. A vial can only hold so much liquid. Check its capacity before choosing a large volume.
Questions
How much bac water should I add to a peptide vial?
The arithmetic can't decide that: any volume works mathematically, it just sets the concentration. The volume should come from the instructions supplied with the vial or from a pharmacist. Once you have a target concentration, or a number of units you want a dose to fill, this calculator gives the matching volume.
What does adding more water change?
Only the concentration. The vial holds the same milligrams whatever you add. More liquid means a lower mg/mL, so each dose takes more units on the syringe. Less liquid means a higher mg/mL and fewer units per dose.
How much water for a 10 mg vial at 5 mg/mL?
10 ÷ 5 = 2 mL of total solution. At that strength each 1 mg is 0.2 mL, or 20 units on a U-100 syringe.
How much water so that 250 mcg is 10 units?
For a 10 mg vial: 10 units is 0.1 mL, so the solution must hold 0.25 mg per 0.1 mL, which is 2.5 mg/mL. 10 ÷ 2.5 = 4 mL. For a 5 mg vial it's 2 mL.
Is the water added the same as the total solution?
Close, not exact. Freeze-dried powder takes up a little volume when dissolved, so the total ends up slightly more than the water added. If a pharmacy label gives a final volume or mg/mL, use that.
Is bacteriostatic water the same as sterile water?
No. Bacteriostatic water contains a preservative (usually 0.9% benzyl alcohol) and is meant for multiple-dose use; sterile water for injection has none. Which one a product needs is part of its instructions, not something a calculator can decide.