How to use (3 steps)
- Select an example or enter dilution (10 exponent), plated volume (mL), and colony counts.
- Choose a guide range (e.g., 30–300) and review selected plates (you can override manually).
- Results (CFU/mL, summaries, plot) are shown (auto updates if enabled).
Inputs (dilution, plated volume, colonies)
Results (CFU/mL)
Summary by dilution
| Dilution | n | Mean CFU/mL | SD (sample) |
|---|
Plot (log10)
Dilution and CFU/mL can span orders of magnitude, so a log10 scatter plot is shown as a guide.
Export
How it’s calculated
- CFU/mL = colonies ÷ (dilution × plated volume)
- If you enter dilution as 10^-6, it is treated as d = 10^(-6).
- Selected rows are averaged (SD shown as sample SD, n-1).
Guide ranges (e.g., 30–300) are not strict rules. Adjust based on your assay.
How to choose rows and read the result
Which dilution rows to use
Start with the rows whose colony counts fall inside your guide range, then confirm that the selected rows represent the same sample and plating setup. If one dilution is overcrowded and another is too sparse, keep the usable row and document why the others were excluded.
30-300 is guidance, not a strict law
The 30-300 range is a common screening rule, not a universal requirement. Keep it as the default filter, but override it when your assay, medium, or counting method uses a different validated range.
How to enter 10^-6 and 0.1 mL
In simple mode, enter -6 for a 10^-6 dilution. In advanced mode, enter 1e-6 directly. For a 100 µL plate, use 0.1 mL as the plated volume.
When replicate averaging makes sense
Average replicates only when they come from the same sample, dilution family, and plated volume assumptions. If you are comparing different dilution choices, use the per-dilution summary first and then decide which rows should contribute to the final mean.
FAQ
Do I have to follow the 30–300 colony count range?
It is a common plating guide, not an absolute rule. You can override the automatic selection if your protocol or organism needs a different range.
Should I enter -6 for the dilution factor?
In simple mode, enter -6 for 10^-6. In advanced mode, you can enter the dilution directly as 1e-6.
What if the plated volume is 0.1 mL?
Enter 0.1 in the plated volume field. Because CFU/mL scales with plated volume, changing 0.1 mL to 1.0 mL changes the final concentration by a factor of 10.
How are replicates summarized?
Selected CFU/mL values are averaged, and the tool shows per-dilution summaries including n, mean, and standard deviation.
Does the share URL include data?
For a small number of rows, data can be included. For many rows, use “share without data.”
Is my data sent anywhere?
No. Calculations run in your browser and inputs are not sent.
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