Serial Dilution Plate Count Calculator

Work out serial dilution plate count instantly with clear inputs, formula shown and shareable results.

About Serial Dilution Plate Count Calculator

Compounds the dilution factor across the serial dilution steps and back-calculates the original viable count from the plate.

Formula

Serial dilution

Total dilution = factor per step^number of steps; original CFU/mL = colonies x total dilution / volume plated

Worked example

With the default values below, Serial Dilution Plate Count Calculator returns Original concentration of 68,000,000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Colonies on the plateaccepts 1–1,000: 68
Number of dilution stepsaccepts 1–12: 5
Dilution factor per stepaccepts 2–1,000: 10
Volume platedaccepts 0.001–10 mL: 0.1 mL

Results

Original concentration: 68,000,000 CFU/mL
Total dilution applied: 100,000
Log10 CFU/mL: 7.833
Dilution as a power of ten: 5.00

Step by step

1Values used
2Serial dilution
3Original concentration= 68,000,000 CFU/mL
4Total dilution applied= 100,000
5Log10 CFU/mL= 7.833
6Dilution as a power of ten= 5.00

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why serially dilute at all?

Undiluted samples give uncountable plates, and a series guarantees at least one plate in the countable range.

What causes dilution error?

Pipetting error compounds multiplicatively, so a 5% error at each of six steps can shift the result by a third.