Serial Dilution Calculator
Compute the concentration at each tube of a serial dilution series from a starting concentration, a fixed fold factor per step and the number of steps.
How it works
total dilution = fold ^ steps · concentration at tube n = C₀ ÷ fold ^ n · final concentration = C₀ ÷ fold ^ steps
A serial dilution repeats the same fold dilution across a row of tubes, so each tube is the previous one divided by the fold factor. After n steps the cumulative dilution is the fold raised to the power n, which is why serial dilutions span many orders of magnitude with small, accurate transfers — a 10-fold series over six steps covers a millionfold range. This is the workhorse method for plate counts, standard curves and titrations where a single big dilution would be imprecise.
Worked example
Starting at 1,000,000 CFU/mL with a 10-fold dilution over 6 steps, the cumulative dilution is 10⁶ = 1,000,000×, so the final tube holds 1,000,000 ÷ 1,000,000 = 1 CFU/mL. Each intermediate tube steps down by a clean factor of ten.
Sources: Serial dilution — Wikipedia
Frequently asked questions
Why dilute serially instead of all at once?
Pipetting a tiny volume for a large single dilution is imprecise and error-prone. Repeating a modest fold step keeps every transfer in an accurate volume range while still reaching very low concentrations.
How do I mix a 10-fold step?
Transfer 1 part of the previous tube into 9 parts of fresh diluent (for example 100 µL into 900 µL), mix well, then repeat into the next tube. Each transfer divides the concentration by ten.
How many tubes are in the series?
The number of steps plus one, because the undiluted stock counts as tube zero. Six dilution steps therefore fill seven tubes including the stock.
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Educational estimate, not medical or laboratory advice — verify formulas, units and assumptions for your specific protocol.