How to use this calculator
- Enter the stock concentration.
- Enter the lower target concentration in the same unit.
- Enter the desired final volume.
- Calculate and measure the displayed stock and diluent volumes.
#3280 · Science & Engineering Tool
Bacterial Growth Dilution Factor Calculator
Determine the dilution factor and mixing volumes needed to reduce a bacterial culture stock to a target concentration. The calculator uses C1V1 = C2V2, returns the required stock and diluent volumes, and states the stock-to-final ratio. Enter stock and target concentrations in the same unit.
Calculator
Laboratory inputsFormula
Dilution factor = stock concentration ÷ target concentration
Stock volume = target concentration × final volume ÷ stock concentration
Stock volume = target concentration × final volume ÷ stock concentration
Diluent volume equals final volume minus stock volume.
What the result means
The main result expresses how many times more concentrated the stock is than the target. The calculated stock aliquot and diluent add to the requested final volume.
This calculator assumes ideal, additive volumes and a homogeneous stock. Mix the stock before sampling and verify concentration when the protocol requires it.
Example calculation
Diluting 1,000,000 cells/mL to 100,000 cells/mL for a final volume of 50 mL requires a 10× dilution: combine 5 mL of stock with 45 mL of diluent.
Tips for better results
- Mix the stock thoroughly before removing an aliquot.
- Use serial dilutions when the required aliquot is too small to measure accurately.
- Keep concentration units identical.
- Account for viability if the count includes nonviable cells.
- Recount after dilution when accuracy is critical.
Frequently asked questions
Why must target concentration not exceed stock concentration?
Adding diluent can only lower concentration; a higher target would require concentration rather than dilution.
Can stock and target concentrations use different units?
Convert them to the same unit before entry.
When should I use a serial dilution?
Use serial steps when the direct stock aliquot is below the reliable range of your pipette or dispenser.
Does the diluent volume include the stock aliquot?
No. Stock volume plus diluent volume equals the entered final volume.
Does the calculator adjust for cell viability?
No. Enter a viable concentration if your target is based on viable cells.
Related calculators
Dilution variables
| Variable | Unit | Meaning |
|---|---|---|
| Stock concentration | cells/mL | Starting concentration |
| Target concentration | cells/mL | Desired final concentration |
| Final volume | mL | Stock plus diluent |