Large dilutions made in a single step force you to pipette tiny, error-prone volumes from a concentrated stock. A serial dilution spreads the job across several equal steps. This planner picks the even fold factor and hands you a tube-by-tube pipetting recipe.
How it works
The total dilution is the stock divided by the target. To split it evenly over
N steps the planner takes the Nth root: fold = (stock / target)^(1/N). Every
tube then uses the same fold, so a 100-fold dilution over three steps becomes
three steps of about 4.64-fold each.
For a fixed tube volume V, the source you carry forward is V / fold and the
diluent is the remainder. Tube 1 draws from the stock, and each later tube draws
from the tube before it. This keeps C1V1 = C2V2 satisfied at every step.
Worked example
Diluting a 1000 ng/mL stock to 10 ng/mL over three steps into 1000 µL tubes gives a 4.64-fold step. Each tube takes 1000 / 4.64 = 215 µL of source plus 785 µL diluent, producing concentrations of about 215, 46, and 10 ng/mL.
Tips
Mix each tube thoroughly before drawing into the next, and change tips between steps to avoid carryover. Keep transfer volumes above roughly 20 µL for accuracy. If a transfer comes out too small, add a step or increase the tube volume so the pipetting stays reliable.