Dilution Factor and Serial Dilution Calculator

How Dilution Factor Is Calculated

The dilution factor describes how much a solution has been diluted from its original concentration. It’s used in microbiology (serial dilutions), chemistry (preparing standard solutions), and clinical labs.

Dilution Factor Formula: DF = V_final / V_initial = C_initial / C_final

C1V1 = C2V2 (Dilution Equation): C1 × V1 = C2 × V2

Where:

• C1 = initial concentration
• V1 = volume of stock solution taken
• C2 = final (diluted) concentration
• V2 = final total volume

Worked Example: Preparing 500 mL of a 0.1 M NaCl solution from a 2.0 M stock:

• V1 = (C2 × V2) / C1 = (0.1 × 500) / 2.0 = 25 mL of stock
• Add 25 mL stock → dilute to 500 mL total with water
• Dilution factor = 500 / 25 = 1:20

Serial Dilutions (Microbiology): Each step multiplies the dilution factor:

• Tube 1: 0.1 mL sample + 0.9 mL diluent = 1:10 (10⁻¹)
• Tube 2: 0.1 mL from tube 1 + 0.9 mL = 1:100 (10⁻²)
• Tube 3: 0.1 mL from tube 2 + 0.9 mL = 1:1,000 (10⁻³)

Colony Count Formula: CFU/mL = Colony Count / (Dilution Factor × Volume Plated mL)

If 45 colonies on 10⁻⁴ plate, 0.1 mL plated:

• CFU/mL = 45 / (0.0001 × 0.1) = 4.5 × 10⁶ CFU/mL