Serial Dilution Calculator
Plan a dilution series: how much to transfer, how much diluent goes in each tube, and the dilution and concentration of every tube.
Calculator
Plan a series
10 for a 1 in 10 series, 2 for two-fold.
Once mixed, before you take from it.
To see the concentration in every tube.
Enter the dilution factor, number of tubes and volume in each tube to plan the series.
Worked example
A 1 in 10 series of 6 tubes, 1 mL each
- 01F = 10, V = 1 mL
- 02transfer = 1 mL ÷ 10 = 100 µL; diluent = 900 µL
- 03tube 6 = 1/10⁶ of the stock
Put 900 µL of diluent in each tube, then move 100 µL from the stock into tube 1 and from each tube into the next.
How it works
The reasoning behind it
A serial dilution repeats the same small dilution several times. Each tube is diluted F times from the tube before it, so after n tubes the stock is diluted Fⁿ times: six 10-fold steps make a million-fold dilution.
Steps are used because one large dilution is hard to do accurately. A million-fold dilution in one go would mean pipetting 1 µL into a litre.
Each tube's volume V is the diluent put in first plus the transfer from the tube before. For the tube to be F times weaker, the transfer has to be V ÷ F.
Questions
Frequently asked
How do you calculate a serial dilution?
Choose the factor F for each step and the volume V for each tube. Move V ÷ F into V − V ÷ F of diluent, mix, and repeat. Tube n then holds the stock divided by F to the power n.
How do I find the original concentration from a plate count?
Multiply the colonies by the dilution of the tube you plated from, and divide by the volume plated in mL. 45 colonies from 0.1 mL of the 10⁻⁵ tube is 45 × 10⁵ ÷ 0.1 = 4.5 × 10⁷ CFU/mL.
What is a two-fold serial dilution?
A series with a factor of 2: each tube holds half the concentration of the one before. It is used for antibiotic MIC tests and standard curves. Move half of each tube's volume into an equal volume of diluent.
Why use a serial dilution instead of one dilution?
Large dilutions need either very small or very large volumes, and both are hard to measure accurately. A series spreads the dilution over steps you can pipette well, and gives you every concentration in between.
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