How is CFU/mL calculated?

CFU/mL = colonies ÷ (dilution × plated volume). If you enter dilution as 10^-6, it is treated as d = 10^(-6).

What do I enter for 10^-6?

In simple mode, enter the exponent -6. In advanced mode, you can enter 1e-6 directly.

Is the 30–300 range mandatory?

It’s a common guide, but it varies by experiment. Here it is treated as a guide and you can override selection manually.

CFU/mL calculator (dilution, plated volume) | from colony counts

Q: How are replicates summarized?

Selected rows are averaged to estimate CFU/mL, and per-dilution summaries (n, mean, SD) are shown.

Q: Is my data sent anywhere?

No. Calculations run in your browser and data is not sent.

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)

Example preset

Input mode

Simple (exponent) Advanced (decimal)

Simple: enter -6 for 10^-6 (recommended). Advanced: enter 1e-6 directly.

Count range (guide)

Note

—

Plated volume preset (apply to all rows) Dilution series template

Actions

Auto update

Label	Dilution	Plated volume (mL)	Colonies	CFU/mL	Range	Use	Actions

Paste (TSV/CSV)

Recommended columns: Label, log10_dilution, plated_volume_mL, colonies. Advanced mode also supports dilution (1e-6, etc.).

Results (CFU/mL)

Estimated CFU/mL (mean)

—

SD (sample, n-1)

—

Selected plates

—

Selection rule

—

Guide range

—

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.

FAQ

Do I have to follow the 30–300 range?

It’s a common guide but varies by experiment. You can override selection manually.

Should I enter -6 for dilution?

In simple mode, enter -6 for 10^-6. In advanced mode, you can enter 1e-6 directly.

What if plated volume is 0.1 mL?

Enter 0.1 in plated volume (mL). Changing plated volume changes CFU/mL.

How are replicates summarized?

Selected CFU/mL values are averaged and per-dilution summaries (n, mean, SD) are shown.

Does the share URL include data?

For a small number of rows, data can be included. For many rows, use “share without data.”

CFU/mL calculator (dilution & plated volume)