CFU Calculator
Colony Forming Units per mL – CFU/mL = (colonies × dilution) / volume plated
Microbial Enumeration
Plate Count Parameters
10⁻² = 100, 10⁻³ = 1000
Counted colonies (30–300 optimal)
Plate Visualization
Enter colony count
Example Scenarios
Typical Limits by Sample Type
| Sample | Acceptable | Marginal | High |
|---|---|---|---|
| Drinking water | <100 | 100–500 | >500 |
| Food | <1,000 | 1,000–10,000 | >10,000 |
| Urine (midstream) | <10,000 | 10,000–100,000 | >100,000 |
| Environmental air | <500 | 500–2,000 | >2,000 |
Limits vary by regulatory standard (USP, EPA, ISO).
Formula
CFU/mL = (colonies × dilution factor) / volume plated
Example: (150 × 100) / 0.1 = 150,000 CFU/mL
QC Guidelines
- • Count plates with 30–300 colonies
- • Average duplicate plates if within 20%
- • Report as CFU/mL (or CFU/g for solid samples)
- • Use appropriate significant figures (e.g., 1.5 × 10⁵)