CFU per mL Calculator
Estimate colony-forming units per milliliter from plate counts, dilution fractions and plated suspension volumes.
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Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Multiply each plated volume by its dilution fraction. Sum the original-suspension volumes represented by the plates. Add the observed whole colony counts. Divide total colonies by total represented original volume.
Estimated CFU/mL=Σcolonies/Σ(plated mL×dilution fraction)
Worked example
Counts 50 and 55 on two 0.1 mL plates at dilution 0.001 represent 0.0002 mL original suspension and estimate 525000 CFU/mL.
Assumptions and input details
A pooled count-per-original-volume model for compatible replicate plates. Countability, organism identity, plating efficiency and method-specific reporting rules are not inferred. Zero colonies do not establish sterility. No clinical interpretation is provided.
References: FDA: aerobic plate counts
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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