Serial Dilution Calculator

Plan each tube's transfer and diluent volume, or total up a dilution factor.

For a serial dilution with dilution factor DF and a final volume V per tube, transfer V/DF from the previous tube into V - V/DF of diluent. The concentration in tube n is C0 / DFⁿ. For a 10-fold series in 1 mL tubes, move 100 µL into 900 µL each time. The total dilution factor of several steps is the product of the step factors.

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What you enter

Starting concentration (optional)
Dilution factor per step (10, 1:10 or 100+900)
Number of steps
Volume per tube

What you get

Concentration and cumulative dilution for each tube
Transfer and diluent volume per tube
Stock volume used
Total dilution factor for a sequence of dilutions
Table copied as TSV for spreadsheets

Formula

Cₙ = C₀ / DFⁿ   |   transfer = V / DF   |   diluent = V - V / DF   |   DF(total) = DF₁ × DF₂ × … × DFₖ

Each step dilutes the previous tube by the same factor, so concentration falls geometrically. A 1:10 step means 1 part sample in 10 parts total (1 + 9). If every tube must keep its full volume after the next transfer, each earlier tube is made slightly larger to cover what is taken out; the calculator works this backward from the last tube.

Questions

How do you do a 1:10 serial dilution?

Put 900 µL of diluent in each tube. Add 100 µL of sample to the first tube, mix, then move 100 µL from that tube to the next, and repeat. Each tube is 10 times more dilute than the one before.

How do you calculate the dilution factor?

Dilution factor = final volume ÷ sample volume. 100 µL into 900 µL gives 1000 ÷ 100 = 10. For several steps, multiply the factors: three 1:10 steps give 1:1000.

Is a 1:10 dilution the same as 1 to 9?

In biology 1:10 usually means 1 part sample in 10 parts total, which is 1 part sample plus 9 parts diluent. Some chemistry texts use 1:9 for the same mix, so state the volumes to avoid confusion.

How do I work out the original concentration from a dilution?

Multiply the concentration measured in the diluted tube by the total dilution factor. For plate counts, CFU/mL = colonies ÷ (volume plated in mL × dilution).

What is the concentration after each step of a 2-fold serial dilution?

It halves each time: C0/2, C0/4, C0/8 and so on. After n steps it is C0/2ⁿ.

References

Ben-David A, Davidson CE (2014). Estimation method for serial dilution experiments. J Microbiol Methods 107:214-221.
Madigan MT, Bender KS, Buckley DH, Sattley WM, Stahl DA (2021). Brock Biology of Microorganisms, 16th ed. Pearson.