Microbiology Calculators

Practical calculators for common microbiology laboratory, dilution, culture and quantitative problems.

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Colony Count — CFU/mL

Calculate viable microbial concentration from colony counts.

CFU/mL — Quick Manual

  1. Enter dilution exponent: -5 for 10⁻⁵.
  2. Enter plated volume in mL.
  3. Enter colony counts.
  4. Click Calculate CFU/mL.
Example: 10⁻⁵, 0.1 mL, 126 + 132 colonies.
10 ^
Example: -5 = 10⁻⁵

Colony Count — CFU/g

Calculate viable microbial concentration per gram of sample.

CFU/g — Quick Manual

  1. Enter dilution exponent.
  2. Enter plated volume in mL.
  3. Enter sample mass represented in the calculation.
  4. Enter mean colony count and calculate.
Example: 10⁻⁴, 0.1 mL, 1 g, 85 colonies.
10 ^

Dilution Factor

Calculate the dilution factor from initial and final concentrations.

Dilution Factor — Quick Manual

  1. Enter the initial concentration.
  2. Enter the final concentration.
  3. Click Calculate.
Example: 1000 → 100 gives 1:10.

Serial Dilution

Generate a serial dilution sequence.

Serial Dilution — Quick Manual

  1. Enter starting dilution exponent.
  2. Select the step dilution.
  3. Enter number of tubes.
  4. Click Generate.
Example: Start -1, step 1:10, 6 tubes.
10 ^

C₁V₁ = C₂V₂

Calculate stock volume and diluent volume.

C₁V₁ = C₂V₂ — Quick Manual

  1. Enter stock concentration C₁.
  2. Enter desired concentration C₂.
  3. Enter final volume V₂.
  4. Click Calculate.
Example: C₁ = 1000 µg/mL, C₂ = 100 µg/mL, V₂ = 10 mL.

Percentage Solution

Calculate the amount required for a percentage solution.

Percentage Solution — Quick Manual

  1. Enter desired percentage.
  2. Enter final volume.
  3. Click Calculate.
Example: 5% for 100 mL = 5 g per 100 mL.

Molarity

Calculate molarity from mass, molecular weight and volume.

Molarity — Quick Manual

  1. Enter mass in grams.
  2. Enter molecular weight.
  3. Enter volume in litres.
  4. Click Calculate.
Formula: M = mass ÷ MW ÷ volume.

Normality

Calculate normality using mass, equivalent weight and volume.

Normality — Quick Manual

  1. Enter mass in grams.
  2. Enter equivalent weight.
  3. Enter volume in litres.
  4. Click Calculate.
Formula: N = mass ÷ equivalent weight ÷ volume.

ppm Calculator

Calculate ppm for dilute aqueous solutions using mg/L.

ppm — Quick Manual

  1. Enter solute amount in mg.
  2. Enter solution volume in litres.
  3. Click Calculate.
Example: 25 mg in 5 L = 5 ppm.

Microbial Growth / Generation Time

Calculate number of generations, generation time and growth rate.

Growth — Quick Manual

  1. Enter initial cell number N₀.
  2. Enter final cell number Nₜ.
  3. Enter time in the same unit throughout.
  4. Click Calculate.
Example: N₀ = 100, Nₜ = 800, time = 3 h.

Log Reduction

Calculate microbial log reduction and percentage reduction.

Log Reduction — Quick Manual

  1. Enter initial microbial count.
  2. Enter final microbial count.
  3. Click Calculate.
Example: 1,000,000 → 10,000 = 2-log reduction.

Hemocytometer Cell Count

Estimate cells/mL from a hemocytometer count.

Hemocytometer — Quick Manual

  1. Enter mean cells counted per large square.
  2. Enter dilution factor.
  3. Enter chamber depth in mm.
  4. Click Calculate.
Example: 85 cells, dilution factor 10, depth 0.1 mm.

MIC / MBC Comparison

Calculate the MBC/MIC ratio for comparison.

MIC / MBC — Quick Manual

  1. Enter MIC.
  2. Enter MBC using the same units.
  3. Click Calculate.
Example: MIC = 2 µg/mL, MBC = 4 µg/mL.

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