A serial dilution is the standard way labs prepare a range of known concentrations from a single stock solution — used in microbiology plating, antibody/ELISA titration, standard curves for qPCR and other assays, and any protocol that needs several concentrations spaced by a constant factor. This calculator runs the step-by-step series math, the per-tube transfer and diluent volumes, and the overall fold-dilution from one set of inputs.
How the Serial Dilution Calculator works
In a serial dilution, each tube is made from the tube before it rather than from the stock directly — except the first tube, which comes from the stock. Because the reduction happens step by step, the concentration at step n equals the stock concentration divided by the dilution factor raised to the n-th power (DFⁿ). This compounding is why a modest per-step factor, such as a 10-fold dilution, produces an enormous overall reduction after only a handful of steps — five 10-fold steps already gives a 100,000-fold overall dilution. It's also why the concentration chart uses a logarithmic y-axis: on a linear scale, later steps would look indistinguishable from zero even though they aren't.
Inputs and what they mean
Stock concentration is the starting value of your undiluted solution, in whatever unit you're tracking — ng/mL, CFU/mL, molarity, or any other consistent concentration unit. Dilution factor per step must be greater than 1; common choices are 2 for doubling dilutions (e.g. antibody titration) and 10 for log dilutions (e.g. microbiology plating). Number of steps is how many tubes come after the stock. Volume per tube is the final volume, in milliliters, that each tube should hold once the transferred aliquot and diluent are combined — it determines the transfer and diluent volumes on the Volumes tab, but it does not affect the concentration series, since concentration only depends on the stock and the dilution factor.
Limits and edge cases
The dilution factor must be greater than 1 — a factor of exactly 1 means no dilution happens at all, and a factor below 1 would require a negative diluent volume, which isn't physically meaningful. Very large step counts combined with large factors can produce vanishingly small concentrations that are easy to misread on a linear scale, which is why this calculator always charts the series on a log axis. The calculator assumes perfect mixing and pipetting at every step; in practice, small pipetting errors compound across a series the same way the concentration does, so a longer series carries more cumulative uncertainty than a short one.