Printed on the vial label.
The total volume of diluent you put into the vial.
Syringe size (U-100)
Draw to
10 units
- Your dose
- 250 mcg = 0.25 mg
- Volume
- 0.1 mL
- Concentration
- 2.5 mg/mL
- Doses in this vial
- 20
| 5 units | 0.125 mg |
|---|---|
| 10 units | 0.25 mg |
| 20 units | 0.5 mg |
| 30 units | 0.75 mg |
| 50 units | 1.25 mg |
The starting values are examples. Replace them with what is on your vial label and prescription. This tool does the arithmetic only and does not recommend a dose.
Choosing how much water to add
The water volume does not change how much drug you have. It changes how strong each drop is, and so how easy the dose is to measure.
- Less water gives a stronger solution and a smaller draw. Small draws are harder to measure and small errors matter more.
- More water gives a weaker solution and a larger draw. It must still fit in the syringe and in the vial.
Try different volumes above until the result lands on a printed mark. The table under the result shows what each mark holds at that concentration.
Worked example
A 5 mg vial with 2 mL of water and a 250 mcg dose:
- 5 mg ÷ 2 mL = 2.5 mg/mL
- 0.25 mg ÷ 2.5 mg/mL = 0.1 mL
- 0.1 mL × 100 = 10 units
- 5 mg ÷ 0.25 mg = 20 doses in the vial
The unit marks are explained in how to read an insulin syringe.
Common questions
What does reconstitution mean?
It means dissolving a freeze-dried powder in a measured amount of sterile liquid so it can be drawn into a syringe.
How much water should I add?
Any amount gives the same total drug, so the choice is about measurement. Pick a volume that puts your dose on a printed mark and well above the first one. Follow the instructions from your pharmacy or prescriber if they give a volume.
How many doses are in my vial?
Divide the amount in the vial by your dose. A 10 mg vial at 0.25 mg per dose holds 40 doses. Real vials lose a little to the needle and stopper.