Colony Forming Unit (CFU/mL) Calculator

Calculate the concentration of viable microorganisms in a sample from your serial dilution plate counts. This tool helps you accurately determine CFU/mL and flags results that are outside the ideal counting range.

Final Concentration

0 CFU/mL

Calculation Steps:


            


            

                    
                    
Plates with colony counts between 30 and 300 are considered ideal for ensuring a statistically significant result.

            

            
        

    






				

				

					

		

					

		

				

						

					

			

						

				

					
CFU/mL Calculator – Simplify Microbial Quantification
				

				

				

				

									
Welcome to the Colony Forming Unit (CFU/mL) Calculator on PharmacyFreak.com. This tool helps you calculate the number of viable microorganisms in a sample using colony counts from plate dilution experiments.
Whether you’re conducting a sterility test, performing a microbial limit test, or just learning microbiology, this calculator will guide you step-by-step and give you accurate, scientifically valid results.
								

				

					

		

					

		

				

						

					

			

						

				

					
What Is CFU/mL?
				

				

				

				

									
Colony Forming Units per Milliliter (CFU/mL) is the number of living, growing bacteria or fungi in 1 mL of your original sample. It is calculated from:
  • The number of colonies on an agar plate
  • The dilution factor used
  • The volume you plated
The formula is:
CFU/mL = (Number of Colonies × Dilution Factor) / Volume Plated (in mL)
This calculator applies that formula, averages your replicates, and gives you clean, easy-to-read output.
								

				

					

		

					

		

				

						

					

			

						

				

					
Key Features of the CFU/mL Calculator
				

				

				

				

									
✅ Add Multiple Plate Counts
You can enter data for multiple replicate plates. The tool calculates the average colony count, which improves accuracy and helps detect outliers.
✅ Easy Dilution Factor Selection
Choose from common dilution factors like:
  • 10³
  • 10⁴
  • 10⁵
    Or select “Other” to enter a custom value. No manual math needed.
✅ Flexible Volume Units
Enter the plated volume in µL (microliters) or mL (milliliters). The tool converts it automatically for calculation.
✅ Quality Flags Based on 30–300 Rule
The tool checks if your average colony count is:
  • ✅ Ideal (30–300) – reliable and valid
  • ⚠️ TFTC (<30) – Too Few To Count
  • ⚠️ TNTC (>300) – Too Numerous To Count
This helps ensure your results are statistically sound.
✅ Step-by-Step Calculation
The calculator shows how the result was computed. You’ll see the exact numbers substituted into the formula—great for learning and checking your work.
✅ One-Click PNG Export
Download your complete calculation, result flags, and formula breakdown as a PNG image. Add it to:
  • Digital lab notebooks
  • Reports
  • Study notes
✅ Built-In Tooltips
Each input field has a (i) icon. Hover or tap to read definitions and examples. Learn as you calculate.
								

				

					

		

					

		

				

						

					

			

						

				

					
How to Use the Calculator – Step-by-Step
				

				

				

				

									
Step 1: Enter Colony Counts
  • Type in the number of colonies from your first plate
  • Click “+ Add Plate” for more replicates
  • The calculator will automatically compute the average
Step 2: Enter the Dilution Factor
  • Select the correct dilution factor from the dropdown
  • If your dilution is not listed, choose “Other” and enter the exact number
    • Example: For a 10⁻⁴ dilution, enter 10,000
Step 3: Enter Volume Plated
  • Enter the amount of diluted sample plated on the agar
  • Choose the correct unit: µL or mL
Step 4: Click “Calculate CFU/mL”
  • The result appears instantly
  • You’ll see the final CFU/mL value
  • A color-coded badge tells you if the count is ideal, too low, or too high
  • Below that, see the full formula breakdown
								

				

					

		

					

		

				

						

					

			

						

				

					
Understanding the 30–300 Rule
				

				

				

				

									
A good colony count falls between 30 and 300. This rule helps ensure accuracy.
✅ Ideal Count (30–300 Colonies)
  • Statistically reliable
  • Easy to count
  • Not overcrowded
  • Best for final result
⚠️ TFTC – Too Few To Count (<30 Colonies)
  • Low accuracy
  • A single error can skew the result
  • Use a plate from a lower dilution if possible
⚠️ TNTC – Too Numerous To Count (>300 Colonies)
  • Overcrowded colonies may merge
  • Some colonies may not form at all
  • Use a plate from a higher dilution instead
This tool automatically applies the 30–300 rule and tells you what to do.
								

				

					

		

					

		

				

						

					

			

						

				

					
Example Calculation
				

				

				

				

									
Imagine this scenario:
  • Colonies counted: 110
  • Dilution Factor: 10,000
  • Volume plated: 100 µL = 0.1 mL
CFU/mL = (110 × 10,000) / 0.1 = 11,000,000
The result is:
1.10 × 10⁷ CFU/mL
If 3 plates had colony counts of 100, 110, and 120, the calculator would average them and update the result accordingly.
								

				

					

		

					

		

				

						

					

			

						

				

					
Why This Tool Is Great for Pharmacy and Microbiology Students
				

				

				

				

									
This CFU calculator helps you:
  • Learn the correct way to calculate microbial load
  • Avoid common mistakes in dilution math
  • Get clean, professional results for your lab reports
  • Understand why quality flags (TFTC/TNTC) matter
  • Save time and focus more on interpreting data
It’s your microbiology lab assistant—accurate, fast, and educational.