Serial dilution calculator
Enter the stock concentration, the dilution factor of each step (10 for 1:10, 2 for 1:2) and the number of tubes, up to twelve. Give the volume you want in each tube and the calculator tells you how much to transfer from the previous tube and how much diluent to add.
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How to use it
- Enter the stock concentration and pick its unit; the unit only labels the results.
- Enter the dilution factor per step and the number of tubes.
- Enter the volume each tube should hold, and read the transfer and diluent volumes and the concentration of every tube.
- Tube i: Cᵢ = C₀ ÷ Fⁱ.
- Total dilution: Fⁿ for n steps.
- Volumes: transfer V ÷ F from the previous tube, add V − V ÷ F of diluent.
Worked example
Stock 1 mg/mL, five 1:10 steps, 1 mL per tube: each tube gets 0.1 mL of the previous one and 0.9 mL of diluent. The tubes hold 0.1, 0.01, 0.001, 0.0001 and 0.00001 mg/mL, a total dilution of 100,000.
Stock 100 µM, three 1:2 steps of 200 µL: transfer 100 µL into 100 µL of diluent, giving 50, 25 and 12.5 µM.
Tips
- Mix well before each transfer, and change pipette tips between tubes so you do not carry over stock.
- Every tube except the last ends with V − V ÷ F after you take the transfer out; make a little extra if you need the full volume in each.
- For plate counts, combine the dilution with the colony count in the CFU calculator.
Frequently asked questions
What is a serial dilution?
A series of dilutions in which each tube is made from the one before, always by the same factor. Five 1:10 steps turn a 1 mg/mL stock into 0.1, 0.01, 0.001, 0.0001 and 0.00001 mg/mL, a total dilution of 1:100,000.
How do I work out the volumes for each tube?
For a final volume V per tube and a factor F, transfer V ÷ F from the previous tube into V − V ÷ F of diluent. For 1 mL tubes and 1:10 steps, that is 0.1 mL of sample into 0.9 mL of diluent.
What is the difference between dilution factor and dilution ratio?
A dilution factor of 10 means 1 part sample in 10 parts total, written 1:10 in most labs. Some write it as a 1:9 ratio of sample to diluent. This calculator uses the factor, total volume ÷ sample volume.
How do I find the concentration after n steps?
Divide the stock by the factor raised to the number of steps, C = C₀ ÷ Fⁿ. Five 1:10 steps divide by 10⁵ = 100,000.