Dilution Factor Calculator
The dilution factor describes how much a sample has been diluted. It is defined as the ratio of the final volume to the sample (stock) volume taken. A dilution factor of 10 means the sample was diluted to one-tenth of its original concentration. Knowing the dilution factor lets you recover the original concentration from a measurement on the diluted sample. Enter the sample volume and final volume (in the same units) to calculate the dilution factor and the resulting concentration from your stock.
Dilution factor formula
DF = final volume / sample volume C(diluted) = C(stock) / DF
Sample volume and final volume must be in the same units. The dilution factor is dimensionless. C(diluted) is in the same concentration units as C(stock).
Common dilution ratios
- 1:2 dilution: 1 mL sample + 1 mL diluent = 2 mL total. DF = 2.
- 1:10 dilution: 1 mL sample + 9 mL diluent = 10 mL total. DF = 10.
- 1:100 dilution: 0.1 mL + 9.9 mL = 10 mL. DF = 100.
- 1:1,000 serial dilution: three successive 1:10 dilutions. Overall DF = 10 x 10 x 10 = 1,000.
- To recover the original concentration, multiply the measured value by the dilution factor.
Frequently asked questions
What is the dilution factor?
The dilution factor (DF) is the ratio of the final volume of the diluted solution to the volume of stock solution (sample) taken. DF = final volume / sample volume. A DF of 10 means the solution was diluted 10-fold.
How is dilution factor different from concentration ratio?
Dilution factor is the fold-dilution applied to the sample. The concentration ratio is the inverse: if the dilution factor is 10, the final concentration is 1/10 of the original. Concentration final = concentration initial / dilution factor.
What is a 1:10 dilution?
A 1:10 dilution means 1 part sample is added to 9 parts diluent, giving a final volume 10 times the sample volume. The dilution factor is 10 and the final concentration is 1/10 of the original.
How do I calculate serial dilution factor?
For a serial dilution, the overall dilution factor equals the product of individual dilution factors at each step. For three 1:10 dilutions in series, the overall DF = 10 * 10 * 10 = 1,000.
Why is dilution factor important in microbiology?
In microbiology, colony-forming unit (CFU) counts require knowing the dilution factor to back-calculate the concentration in the original sample. The original concentration = CFU count / (plated volume * dilution factor).
Official sources
- IUPAC Gold Book: Dilution factor definition.
- NIST: NIST Weights and Measures.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.