Colony Forming Units
Calculator
Results
- Viable count (CFU/mL)
- 156,000,000
- log₁₀ CFU/mL
- 8.193124
- Viable count (CFU/L)
- 156,000,000,000
Biology and lab results
| Viable count (CFU/mL) | 156,000,000 |
| log₁₀ CFU/mL | 8.193124 |
| Viable count (CFU/L) | 156,000,000,000 |
formula-map diagram
- Viable count (CFU/mL)
- 156,000,000
- log₁₀ CFU/mL
- 8.193124
- Viable count (CFU/L)
- 156,000,000,000
Formula breakdown
Formula
CFU/mL = colonies ÷ (volume plated × dilution factor)= 156000000
Note
Simplified model: these results use standard textbook laboratory relationships and average constants (A260 = 1 for 50 µg/mL dsDNA, 617.96 g/mol per base pair, ~110 Da per amino acid, ideal exponential growth). Real samples vary with purity, contaminants, buffer, temperature and instrument calibration. Always confirm against your own standards and protocol; do not use for diagnostic or safety-critical work.
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See all →Frequently asked questions
What does CFU/mL actually represent?+
A colony-forming unit is one viable cell or cell cluster capable of growing into a visible colony, so CFU/mL estimates the concentration of viable, culturable organisms in the original sample, not the total cell count. Dead or non-culturable cells are not counted, which is why CFU can be lower than a microscope-based total cell count.
What is the formula behind the calculator?+
CFU/mL equals the number of colonies counted, divided by the volume plated, divided by the dilution factor of that plate: colonies / (volume in mL x dilution factor). The calculator simply automates this so you do not need to track the dilution arithmetic by hand.
Which plate should I use if I diluted a sample multiple ways?+
Choose the plate with a countable number of colonies, typically 30 to 300, since plates with fewer colonies carry more statistical noise and plates with more suffer from overlapping colonies. Standard practice is to average results from plates in that countable range across replicate dilutions.
What if my plate has too few or too many colonies to count reliably?+
Fewer than 30 colonies gives a result with wide statistical uncertainty, and more than 300 colonies likely means the count is undercounted due to overlap; in both cases redo the plating at a dilution that lands in the 30-300 range rather than relying on the calculator's output.
Why does the same sample give different CFU/mL from different labs?+
CFU counts depend heavily on plating technique, incubation temperature and time, and the growth medium used, since not all viable organisms form colonies under identical conditions. Comparing CFU/mL figures is only meaningful when the plating method and incubation conditions are the same.