Only plates with 30 to 300 colonies count
Below 30 the count is dominated by random variation; above 300 colonies merge and crowd each other out, so the count understates the true number. Standard microbiological practice discards plates outside that window entirely rather than correcting them, which is why serial dilutions are plated in a range.
What this page needs from you
This page asks for colonies counted, dilution factor in × and volume plated in mL. From those it returns cfu per ml, together with in scientific notation, colonies counted, countable range check and total cfu in 100 ml. Every figure updates as you type, and nothing you enter leaves your browser.
Reproducibility depends on the inputs
The arithmetic here is exact; the measurements feeding it usually are not. Pipetting error, incomplete mixing and drift in a spectrophotometer all propagate straight through. Where a result matters, run it in duplicate and compare rather than trusting a single reading.
The formula
CFU/mL = colonies × dilution factor ÷ volume plated
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the CFU Calculator
- Fill in each field with your own figures — the defaults are only there as an example.
- The result updates as you type, so there is no button to press.
- Check the breakdown under the main result for the supporting numbers.
- Use the copy button to take the result with you, or share the link to reload the same inputs.
CFU Calculator — frequently asked questions
Is this cfu calculator free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
How accurate is the result?
The maths is exact for the formula shown on the page. Accuracy in the real world depends on your inputs and on assumptions the formula cannot see, so treat the output as a well-grounded estimate rather than a quote.
Can I use it on my phone?
Yes. The page is responsive, weighs a few kilobytes and works offline once loaded, so it behaves the same on a phone as on a desktop.
What people search for
This page answers each of these searches. They are the exact phrases visitors use to find the cfu calculator.
- cfu calculator
- bacterial count calculator
- plate count calculator
- cfu per ml calculation
- colony forming units
About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed September 14, 2026 · Calculation runs client-side · No data collected · Report an error