Bacterial Dilution Calculator

Calculator Inputs

The page uses a white theme with a single content column, while the input area becomes three columns on large screens, two on medium screens, and one on mobile.

Stock concentration (CFU/mL)

Target concentration (CFU/mL)

Desired final volume (mL)

Preferred serial step factor

Use 10 for a classic tenfold series.

Serial step final volume (mL)

Plating volume (µL)

Replicates

Safety margin (%)

Expected recovery (%)

Available stock (mL, optional)

Example Data Table

Stock Concentration	Target Concentration	Final Volume	Step Factor	Step Volume	Plating Volume	Replicates	Safety Margin	Expected Recovery
1.0e9 CFU/mL	1.0e6 CFU/mL	50 mL	10×	10 mL	100 µL	3	5%	90%

For this example, the adjusted batch volume becomes 52.5 mL, the direct stock transfer is 0.0525 mL, and the dilution factor is 1000×.

Formula Used

Direct dilution equation: C1 × V1 = C2 × V2

Required stock volume: V1 = (C2 × V2) ÷ C1

Diluent volume: Diluent = V2 − V1

Total dilution factor: DF = C1 ÷ C2

Adjusted final volume: Adjusted V2 = Desired V2 × (1 + Safety Margin ÷ 100)

Cells per plate: Cells = Target Concentration × Plating Volume in mL

Recovered cells estimate: Recovered Cells = Cells Across Replicates × (Recovery % ÷ 100)

Serial dilution product: multiply every step factor together. The product should match the target dilution factor.

How to Use This Calculator

Enter the starting stock concentration and the target concentration you need.
Type the final volume you want to prepare, then add any safety margin.
Choose a serial step factor and a step volume for the planner.
Add plating volume, replicates, and recovery percentage for downstream estimates.
Submit the form to view the result summary above the calculator.
Review the graph, serial plan, and warnings before exporting CSV or PDF.

FAQs

1. What does the dilution factor mean?

The dilution factor shows how many times the stock is reduced to reach the target concentration. A 1000× dilution means the final concentration is one-thousandth of the original stock.

2. Why does the calculator show both direct and serial plans?

A direct mix gives the mathematically exact stock and diluent volumes. A serial plan helps when the direct stock transfer is too tiny for comfortable measuring or pipetting.

3. What happens if the target concentration is higher than the stock?

That would require concentration, not dilution. The calculator blocks that request because the direct dilution equation only works when the stock concentration is equal to or greater than the target.

4. Why include a safety margin?

A safety margin increases the prepared volume so small handling losses do not leave you short. It is useful when multiple transfers, repeats, or extra reserve volume are expected.

5. How is the plated cell estimate calculated?

The calculator multiplies target concentration by plating volume in milliliters. It then multiplies by the number of replicates, and optionally scales the total by the recovery percentage.

6. Why might the calculator warn about very small transfer volumes?

Very small volumes can be difficult to measure consistently. The warning suggests increasing step volume or using a smaller per-step factor so the serial plan is easier to handle.

7. Does the graph use a logarithmic scale?

Yes. Dilution series often span large concentration ranges, so a logarithmic vertical axis makes big changes easier to compare without compressing smaller steps into a flat line.

8. Can I export the results for records or reports?

Yes. The page includes CSV export for table data and PDF export for the result block, making it easy to save the calculation summary, serial plan, and graph.