Serial Dilution Calculator
Final concentration after a series of equal dilution steps, with the dilution factor and log reduction.
Results
What this tool does
Serial dilution is how you get from a culture too dense to count to a plate with thirty colonies on it, and how a calibration curve spans four orders of magnitude without ever pipetting a microlitre. Each tube is the same simple step; the power of the method is that the steps multiply. Five tenfold steps is a hundred thousandfold dilution, and any error in one step propagates through every tube after it.
Formula
dilution per pitch = (Vsample + Vdiluent)/Vsample ; final = initial / DF^n
Variables
| Symbol | Meaning | Unit |
|---|---|---|
c0 | Initial concentration | — |
vs | Sample volume | mL |
vd | Diluent per step | mL |
ns | Number of steps | — |
CF | Final concentration | — |
DF | Dilution factor | — |
TF | Total dilution | — |
LG | Log reduction | — |
VT | Volume per tube | mL |
Worked example
- Initial concentration1000
- Sample volume1 mL
- Diluent per step9 mL
- Number of steps5
- Final concentration0.01000000
- Dilution factor10.0000
- Total dilution100,000.00
- Log reduction5.0000
- Volume per tube10.000 mL
Limitations
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.
Frequently asked questions
Is 1 mL into 9 mL a tenfold dilution or a ninefold one?
Tenfold. The dilution factor is the final volume divided by the sample volume, and the final volume is 1 + 9 = 10 mL. The common mistake is to read 1 in 9 as the ratio, which gives a factor of 9 and quietly shifts every tube in the series. Writing it as 1 mL made up to 10 mL removes the ambiguity entirely.