Setting Up a Serial Dilution Series Correctly

A serial dilution — a sequence of dilutions, each one made from the previous — is how you generate a wide concentration range (like a standard curve) without needing a separate stock for every point. Getting the dilution factor consistent across every step matters more than most people initially expect.

How dilution factors compound

If each step in your series is a 1:10 dilution, after 4 steps your concentration isn't 1/40th of the original — it's 1/10,000th (10 × 10 × 10 × 10). Serial dilution is multiplicative, not additive, and small errors in one step propagate through every subsequent one.

A worked example

Starting stock: 1 M. Each step: take 1 part stock + 9 parts diluent (a 1:10 dilution factor).

Where serial dilutions commonly go wrong

• Inconsistent pipetting volumes across steps — even small volume errors compound multiplicatively across a long series
• Not mixing thoroughly between steps — an underused source of error, since an incompletely mixed tube gives you an inaccurate starting point for the next dilution
• Using the wrong tube's concentration as the "stock" for the next step — easy to do when working through many tubes quickly
• Pipette accuracy at very small volumes — most pipettes are less accurate at their lower volume range; if a step calls for an unusually small transfer volume, consider adjusting the dilution factor instead