Serial dilution calculator
Plan a dilution series and get the transfer volume for every step.
Total volume in each tube after mixing.
| Tube | Concentration | 1 in | Transfer | Diluent |
|---|---|---|---|---|
| Stock | 1 M | — | — | — |
| 1 | 100 mM | 10 | 100 µL | 900 µL |
| 2 | 10 mM | 100 | 100 µL | 900 µL |
| 3 | 1 mM | 1000 | 100 µL | 900 µL |
| 4 | 100 µM | 10000 | 100 µL | 900 µL |
| 5 | 10 µM | 100000 | 100 µL | 900 µL |
| 6 | 1 µM | 1000000 | 100 µL | 900 µL |
Cₙ = C₀ ÷ fⁿ, transfer = V ÷ f- Conservation of amount of substance on dilution — IUPAC Compendium of Chemical Terminology (the Gold Book), 2019
When to use this
Use this to plan a dilution series — a standard curve, an MIC plate, a viable count. It gives the concentration at every step and the volumes to move. For a single dilution, the dilution calculator is simpler.
Worked example
A tenfold series from a 1 mg/mL stock, six tubes, 1 mL per tube.
- Stock concentration
- 1 mg/mL
- Dilution factor per step
- 10
- Number of steps
- 6
- Volume per tube
- 1 mL
Result
The series runs 1 mg/mL down to 10 ng/mL, each tube a tenth of the one before it.
What people get wrong
- Not mixing before drawing the next transfer. Every step inherits the one before it, so an unmixed tube propagates its error the whole way down the row.
- Keeping the same tip between steps. Concentrated stock on the outside of the tip carries down the series and flattens the low end.
- Reading the transfer volume as the volume to add to a full tube. A tenfold step into a 1 mL final volume means 111 µL into 889 µL, not 100 µL into 1 mL.
Questions
+Why is the transfer 111 µL and not 100 µL?
Because the tube ends at 1 mL total. One part in ten of the final volume is 100 µL into 900 µL; if you want 1 mL in the tube after adding, the transfer is 1000/9 = 111 µL.
+How many steps before the error matters?
Errors compound multiplicatively, so a consistent 2% pipetting error is about 13% off by the sixth tube. For a standard curve, prepare the extremes independently as a check.
+Can I use a factor other than ten?
Yes. Twofold series are standard for MIC plates and the tool handles any factor above one.
Related tools
- Dilution calculator — Work out how much stock and diluent to combine for a target concentration.
- Molarity calculator — Convert between mass, molar concentration and volume for a solution.
Science last reviewed .