Serial Dilution Planner
Design a serial dilution series for microplate or tube workflows. Enter the starting concentration, the number of steps, the dilution factor (or the final fold dilution), and the working volume per tube or well. The calculator returns the transfer volume at every step, the running concentration, and the cumulative dilution.
Calculator
Enter values and calculate to see the tube-by-tube plan
Final tube concentration
Bench note
Tube-by-tube plan
| Tube | Solvent | Transfer | Dilution | Concentration |
|---|
Vsolvent = Vtransfer ÷ (F − 1) · Cn = Cstock ÷ Fn
A 1:F dilution mixes one part sample with (F − 1) parts solvent, so each tube is pre-filled with transfer volume ÷ (F − 1) of solvent. After mixing, the same volume moves to the next tube, multiplying the dilution by F every step. The concentration of tube n is the stock divided by F raised to n.
About this calculation
What this is
A serial dilution is a stepwise dilution where each tube is diluted from the previous one by a fixed factor (commonly 1:2, 1:5, or 1:10). After n steps, the cumulative dilution is the per-step factor raised to the n-th power.
Why it is used
Spanning several orders of magnitude in a single plate is only practical when each well is a fraction of the previous one. Serial dilutions are the backbone of standard curves, MIC assays, and titer determinations.
Why this calculator exists
Choosing a transfer volume that is both pipettable and accurate across a multi-step series is a small arithmetic loop, but the cumulative fold dilution is easy to mis-state. The calculator returns every step in a single table so you can see the full series before you start.
Key assumptions
- Mixing is perfect at each step (every transfer fully equilibrates before the next withdrawal).
- The working volume per step is large enough to withdraw the transfer volume with the available pipette.
- No evaporation or volume loss occurs between steps.
Limitations
- It does not model cumulative volumetric error; for long series consider an independent verification of the final tube.
- It does not correct for viscous or non-ideal samples.
- It assumes the dilution factor is the same at every step — heterogeneous series need a manual table.
What this calculates
- Per-tube plan
- For each tube: solvent volume, transfer volume, concentration, and dilution vs. stock.
- Final concentration
- Concentration in the last tube, in the stock unit.
- Total dilution
- Dilution factor of the final tube relative to the stock.
- Total solvent volume
- Combined solvent to pre-fill all tubes.
Frequently asked questions
How do I plan a serial dilution with this calculator?
Enter the stock concentration and its unit, the fold-dilution for each step, the transfer volume (with mL or µL units), and the number of tubes (1 to 12). The planner returns a per-tube table — how much solvent to pre-fill each tube with, the volume to transfer, and the concentration after each step — plus the final concentration, total dilution, and total solvent volume to prepare.
How are the tube volumes and step concentrations calculated?
Each tube follows the 1:F convention: 1 part sample plus (F minus 1) parts solvent, so the solvent pre-fill is the transfer volume divided by (F minus 1). The concentration after step i is the stock divided by F raised to the i-th power, and after n tubes the total dilution is F to the power n. For a 10-fold series of 6 tubes with a 1 mL transfer, each tube gets 1/9 mL of solvent before the first transfer and the last tube is diluted 10^6-fold.
What does the dilution factor per step mean, and why must it be greater than 1?
The per-step dilution factor is how many times more dilute each tube is than the one before it: 2 for a two-fold series, 10 for a ten-fold series. A factor of 1 or below describes no dilution at all, so the planner rejects it with an error. Keep the same factor for every tube — the tool applies one uniform fold-dilution across the whole series.
Which concentration units can I use for a serial dilution?
The planner accepts M, mM, µM, mg/mL, µg/mL, cells/mL, and CFU/mL, and every concentration in the results stays in the unit you entered. That makes it usable straight from a stock in µM or from a culture counted in CFU/mL. It only tracks the dilution arithmetic — convert or count plates with a separate tool.
What should I watch out for when planning a dilution series for plate counts?
The planner warns when your transfer volume drops below the 2 µL practical pipetting floor, because small errors compound down the series and the last tube becomes the least accurate. It also flags when the factor and tube count push the total dilution beyond what it can compute precisely — reduce the factor or the number of steps. Note that it plans volumes only; choosing which dilutions will land in your countable CFU range is still your call.
For research and educational use only. Not for clinical or diagnostic decisions. Always verify calculations independently before use in critical applications.