Serial dilution planner
Maintained by the Talindrew team · Last updated
A serial dilution reaches large total dilutions through repeated small ones: transferring volume V into V × (fold − 1) of diluent gives one fold-step; after n steps the total dilution is foldⁿ. Six 10-fold steps (100 µl into 900 µl each time) span a 10⁶ range with every pipetted volume comfortably accurate.
Result
Each step: transfer V into V×(fold−1) of diluent, mix, repeat. Six 10-fold steps span 10⁶, the standard series for qPCR standards and CFU plating. Change tips between tubes; carryover compounds down the series.
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What it looks like
Formula
diluent per step = V_transfer × (fold − 1) · total dilution = foldⁿ
Source: Standard dilution-series arithmetic (vendor serial-dilution guides)
Worked example
Given: 10-fold series, 6 steps, transferring 100 µl per step
- 1.Diluent per tube: 100 × (10 − 1) = 900 µl.
- 2.Transfer 100 µl tube-to-tube, mixing fully each time.
- 3.Total dilution after 6 steps: 10⁶.
Six tubes of 900 µl diluent + 100 µl transfers = 10⁶ range
How the calculation flows
Units & constants
| qPCR standards | 10-fold × 6–8 steps |
|---|---|
| CFU plating | 10-fold × 6–8 steps, plate the last 3–4 |
| ELISA / dose-response | 2- or 3-fold × 8–12 steps |
| Pipetting floor | Keep every transfer ≥ 2 µl (accuracy): raise volumes, not ratios |
| Cross-contamination | Fresh tip every step; carryover compounds down the series |
| Price | Free |
Why dilute serially instead of in one step?
A 10⁶-fold dilution in one step means pipetting 1 µl into a litre, or 0.1 µl into 100 ml, both outside accurate pipetting. Six 10-fold steps keep every volume in the accurate 100–900 µl range, and errors per step combine as the root-sum rather than multiplying catastrophically. The trade-off is that a systematic per-step bias (always under-mixing, tip carryover) compounds exponentially, which is why full mixing and fresh tips per step matter more than pipette calibration.
How do you choose fold factor and steps?
Start from the range you must span and the resolution you need within it. Standard curves want equal log spacing across the unknowns' expected range: 10-fold steps give one point per decade; 2-fold steps give ~3.3 points per decade for tight dose-response work. Then pick a transfer volume that keeps both the transfer and the diluent within your pipettes' accurate ranges.
Frequently asked questions
Three 10-fold steps (100 µl into 900 µl, three times), or two steps of 1:31.6 if tubes are scarce. A single 1 µl-into-1 ml transfer is legal but rides entirely on the accuracy of a 1 µl pipetting event.
Yes: diluent = transfer × (fold − 1). A 2-fold series transfers into an equal volume; a 5-fold series into four volumes; a 10-fold series into nine. The planner computes it for whatever fold you enter.
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