ABOUT
Microbiology tools with transparent working
CFU Calculator is a small collection of browser-based tools for everyday microbiology calculations: CFU enumeration from plate counts, OD600 cell density estimates, and serial dilution planning. The site exists because the same handful of formulas underlie a surprising share of routine bench work, and because those formulas are easy to apply slightly wrong under time pressure.
What the tools do
The CFU calculator converts colony counts into CFU/mL or CFU/g using the dilution fraction and plated volume, with optional countability windows and replicate pooling. The OD600 calculator turns optical density into a cells/mL estimate using a conversion factor, linear curve, or logarithmic model that you supply. The serial dilution planner works out transfer and diluent volumes for each tube and tracks the cumulative dilution through the series. The full list lives on the tools index.
How the calculations work
Every calculator runs locally in your browser — entered values are not sent to a server. Each result is shown with the formula behind it, the substituted values, and the units of each term, so the working can be checked rather than trusted. The calculation methods page lists every equation exactly as the tools implement it, and the guides section expands each topic with worked examples and practical context.
What these tools are not
They perform arithmetic, not validation. A calculator cannot verify that your dilution was mixed properly, that your incubation conditions suit your organism, or that your OD600 calibration still matches your instrument. Results depend entirely on the values and methods entered. Countability limits, calibration ranges, detection limits, and sample preparation should always follow your laboratory's validated procedures. Nothing here replaces professional judgement, an accredited method, or instrument-specific guidance.
Who maintains the site
CFU Calculator is maintained by the site owner. Content is written against standard conventions used in analytical microbiology — for example, countable-range conventions consistent with ISO 7218 practice and standard viable-count formulas — and the methods page documents every formula so errors can be spotted and reported. The site does not claim laboratory validation or institutional endorsement. Found a mistake or a missing edge case? Get in touch with the tool name, the inputs used, and the expected result.