Dilution calculator
Enter what is in the vial and how much diluent goes in, and read the concentration. Or set the concentration you want and read the volume to add.
The volume withdrawn each time, to see what each aliquot contains.
- Concentration
- 2.5 mg/mL
- 2,500 µg/mL
- Each 0.1 mL aliquot contains
- 0.25 mg
- 250 µg; about 20 aliquots from 2 mL
Arithmetic only: concentration = mass ÷ volume. It assumes the substance dissolves fully and adds no volume of its own. What any figure should be is a matter for your own laboratory protocol.
Worked examples
The same arithmetic across common vial contents. Mass divided by volume gives mg/mL; multiply by the aliquot volume to see what each withdrawal contains.
| Substance in vial | Diluent added | Concentration | Per 0.1 mL aliquot |
|---|---|---|---|
| 2 mg | 1 mL | 2 mg/mL | 0.2 mg (200 µg) |
| 5 mg | 1 mL | 5 mg/mL | 0.5 mg (500 µg) |
| 5 mg | 2 mL | 2.5 mg/mL | 0.25 mg (250 µg) |
| 10 mg | 2 mL | 5 mg/mL | 0.5 mg (500 µg) |
| 10 mg | 5 mL | 2 mg/mL | 0.2 mg (200 µg) |
| 50 mg | 5 mL | 10 mg/mL | 1 mg (1,000 µg) |
Units
- 1 mg = 1,000 µg (micrograms). 1 g = 1,000 mg.
- 1 mL = 1 cc. On a 1 mL syringe graduated in 100 units, 0.1 mL is 10 units and 0.5 mL is 50 units.
- mg/mL × aliquot volume in mL = mg in the aliquot.
- A 10 mL vial of diluent yields 10 draws of 1 mL, 20 of 0.5 mL, or 100 of 0.1 mL.
Questions
How is concentration calculated?
Concentration equals the mass of substance in the vial divided by the volume of diluent added. 5 mg dissolved in 2 mL gives 2.5 mg/mL, which is 2,500 µg/mL. Each 0.1 mL aliquot of that solution contains 0.25 mg.
What units does the calculator use?
Milligrams for mass, millilitres for volume, and mg/mL for concentration, with µg shown alongside. 1 mg is 1,000 µg. 1 mL is 100 units on a 100-unit 1 mL syringe scale, so 0.1 mL is 10 units.
Does adding the diluent change the volume?
The calculator assumes the dissolved substance adds no measurable volume, which is a fair approximation for a few milligrams in a millilitre or more. For larger masses the true volume is slightly higher and the true concentration slightly lower.
How many times can a 10 mL vial of diluent be used?
That depends only on how much is withdrawn each time: a 10 mL vial gives ten 1 mL draws or five 2 mL draws. Whatever is left must be discarded 28 days after the stopper is first punctured.
Which diluent does this assume?
Any. The arithmetic is the same for bacteriostatic water, sterile water or saline. The difference between them is the preservative: bacteriostatic water contains a bacteriostatic preservative, which is what allows one vial to be entered more than once.
This tool does arithmetic. It does not recommend any quantity, concentration or use, and it is not a substitute for a laboratory protocol. See the product disclaimer.