The formulas
transfer = V ÷ (DF − 1)
tube n = C₁ ÷ DFn−1
V is the volume you want left in each tube and DF the dilution factor at each step. Each tube starts with V of diluent and receives the transfer from the tube before; the first tube needs V plus one transfer.
Worked example
A 1:3 series of 8 tubes with 100 µL left in each: transfer 100 ÷ (3 − 1) = 50 µL into 100 µL of diluent. Starting at 10 µM, tube 2 is 3.333 µM, tube 3 is 1.111 µM and tube 8 is 4.572 nM. Tube 1 needs 150 µL at 10 µM.
Common questions
Why discard from the last tube?
Every other tube gives away one transfer, so removing the same volume from the last tube leaves all tubes with the same volume.
What if my stock is much more concentrated than tube 1?
The calculator works out an intermediate dilution, made up to the volume you choose, so you never pipette less than your minimum volume.
This calculator is checked against independent calculations before every release. How we check our calculators.