Our Serial Dilution Calculator works out the concentration at every step of a dilution series, plus exactly how much sample and diluent to mix at each tube — useful for lab assays, microbiology plating and standard curve prep.
Serial Dilution Calculator
Serial Dilution Formula
C(n) = C₀ ÷ DF^n
Where C₀ is the starting concentration, DF is the dilution factor per step, and n is the tube number in the series. The sample volume transferred to each new tube equals Final Volume ÷ DF, with the remainder made up of diluent.
What Is Serial Dilution?
Serial dilution is the stepwise process of diluting a stock solution by the same factor at each step, creating a series of progressively lower concentrations. It’s used in microbiology for colony counting, in chemistry for standard curves, and in pharmacology for dose-response testing — anywhere you need a precise, repeatable concentration gradient from a single stock.
Common Dilution Factors and Their Uses
| Dilution Factor | Common Use |
|---|---|
| 1:2 (DF=2) | Fine-resolution titration curves, antibody titers |
| 1:10 (DF=10) | Microbial plate counts (CFU/mL), general lab dilution |
| 1:100 (DF=100) | Rapid wide-range concentration screening |
Tips for Accurate Serial Dilutions
- Use a fresh pipette tip (or rinse thoroughly) between transfers to avoid carrying over extra concentrated solution into the next tube.
- Mix each tube thoroughly before transferring to the next — an unmixed sample gives an inaccurate next-step concentration.
- Label tubes immediately — dilution series look identical and mixing up the order invalidates the whole series.
- Account for pipette accuracy at very small volumes — below ~10 µL, small pipetting errors compound significantly over multiple dilution steps.
FAQs
What is a 1:10 dilution?
A 1:10 dilution means 1 part of your sample combined with 9 parts diluent, giving a total of 10 parts — reducing concentration to 1/10th of the original.
How do I calculate concentration after multiple dilutions?
Divide the starting concentration by the dilution factor raised to the power of the number of dilution steps: C(n) = C₀ ÷ DF^n.
What’s the difference between dilution factor and dilution ratio?
Dilution factor (DF) is the total parts (sample + diluent), e.g. DF=10 for a 1:9 ratio. Dilution ratio describes sample:diluent directly, e.g. 1:9. Both describe the same dilution, expressed differently.
Why do serial dilutions use the same factor at every step?
Using a constant factor (e.g. always 1:10) keeps the math simple and predictable — each tube is exactly one order of magnitude (or whatever factor you choose) more dilute than the last.