Knowledge base
Learn colony counting
Clear, lab-tested guides on counting bacterial colonies on agar plates and turning those counts into CFU/mL. Start with the full method, then dig into the 30–300 rule and CFU calculations — and use the free online colony counter whenever you are ready to count a plate.
How to Count Bacterial Colonies on Agar Plates
A complete, lab-tested guide to counting bacterial colonies on agar plates: method, the countable range, tips for accuracy, and how to turn counts into CFU/mL.
Read guideThe 30–300 Rule: The Countable Range in Plate Counts
What the 30–300 rule is, why the countable range matters for accurate plate counts, and how to handle plates that fall outside the range.
Read guideWhat Is CFU? Colony Forming Units Explained
A clear definition of CFU (colony forming unit): what it measures, why microbiologists use it instead of raw cell counts, and how it is reported.
Read guideHow to Calculate CFU per mL: Formula and Examples
The CFU per mL formula explained step by step, with worked examples, dilution factors, and common mistakes to avoid.
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