Bench Calculators
Seven laboratory routine calculations, each with what it is, what it's for, and how to use it. Values update in real time — comma or dot are accepted as decimal separator.
Interpret zones with EUCAST/BrCAST breakpoints →Concentration
1.42 × 10⁷ CFU/mL
Countable plates: 25–250 colonies (30–300 for standard plate count).
About this calculation
- What it is
- Converts the number of visible colonies on a plate into the actual concentration of viable microorganisms in the original sample, correcting for volume and dilution.
- What it is for
- Central calculation for quantitative analysis: compares the microbial load with the microbiological standards that apply to the sample (food, drinking water or surfaces).
- How to use it
- Count a plate with 25–250 colonies, enter volume (0.1 mL surface, 1 mL pour plate) and the dilution exponent.
| Tube | Cumulative dilution | Factor | 1 mL represents |
|---|---|---|---|
| 1 | 1:10 (0.1) | 1:10 | 0.1 mL |
| 2 | 1:100 (0.01) | 1:10 | 0.01 mL |
| 3 | 1:1,000 (0.001) | 1:10 | 0.001 mL |
| 4 | 1:10,000 (0.0001) | 1:10 | 0.0001 mL |
| 5 | 1:100,000 (0.00001) | 1:10 | 0.00001 mL |
| 6 | 1:1,000,000 (0.000001) | 1:10 | 0.000001 mL |
Each 1 mL of the last tube represents 0.000001 mL of the original sample.
About this calculation
- What it is
- Calculates the dilution factor per tube and the accumulated final concentration in a series, essential for plate counting.
- What it is for
- Standardizes microbial load reduction to reach the countable range (25-250 colonies), allowing quantification of high-density samples.
- How to use it
- Enter the transferred aliquot volume, the diluent volume per tube, and the number of tubes in the series.
Stock volume (V₁)
0.01 mL
Diluent to add: 9.99 mL
About this calculation
- What it is
- Relationship describing how much concentrated solution is needed to get a final volume at a lower concentration — the math behind every dilution.
- What it is for
- Used for preparing serial dilutions, adjusting inocula, diluting antibiotics for MIC, and preparing reagents from stocks.
- How to use it
- Enter stock concentration in C₁, desired concentration in C₂ and final volume in V₂: result is how much stock to pipette, rest is diluent.
Estimated density
1.5 × 10⁸ CFU/mL
0.5 McFarland (≈1.5 × 10⁸ CFU/mL) is the standard inoculum for disk diffusion.
About this calculation
- What it is
- Series of turbidity standards that estimates cells per milliliter in a bacterial suspension by comparison or spectrophotometry.
- What it is for
- Standardizes inoculum before antibiogram, MIC tests, and automated identification — non-standard inoculum invalidates the report.
- How to use it
- Adjust suspension until it matches the standard against a black-lined background, enter McFarland and inoculate within 15 minutes.
Generations
9
Generation time
20 min
About this calculation
- What it is
- Measures how many times the population doubled in an interval (generations) and the average time each doubling takes during exponential phase.
- What it is for
- Allows predicting when a culture reaches desired density, comparing media/temperatures, and estimating risk in poorly refrigerated food.
- How to use it
- Enter initial count, final count, and the interval between readings, always within exponential phase.
Mass to weigh
19 g
Autoclave at 121 °C / 1 atm for 15 min; heat-sensitive agars must be filtered.
About this calculation
- What it is
- Converts the concentration on the dehydrated medium label to the exact mass to weigh for your actual volume.
- What it is for
- Prevents weak media (atypical growth) or concentrated media (inhibition), ensuring reproducibility and saving reagent.
- How to use it
- Read g/L on the label, enter your desired volume and weigh the indicated mass.
Result
1,000 mg
In dilute aqueous solutions, 1 mg/L equals 1 µg/mL — the usual MIC breakpoint unit.
About this calculation
- What it is
- Tool to convert between bench units — mass, volume, concentration, time, and temperature — maintaining exact equivalence.
- What it is for
- Avoids scale errors when weighing reagents, pipetting microvolumes, converting antibiotic concentrations (µg/mL ↔ mg/L), and adjusting temperatures.
- How to use it
- Choose category, select source and target units, and enter value: result appears immediately.