How to use
- Enter the starting concentration, the dilution factor and the number of steps. Ten-fold across five steps means a factor of 10 and 5 steps.
- Total volume per tube is optional. Leave it blank and you get the concentration at each step; fill it in and the transfer volume and diluent volume are worked out as well.
- Editing a cell in the Dilution factor column lets a step differ from the rest. Change any one of them and the field above switches to ‘Custom’.
- [Same factor throughout] puts them back. An empty cell follows the shared factor above.
- Results update as you type. There is no calculate button.
Formula & notes
A serial dilution reaches a wide range of concentrations by repeating the same small dilution. Going ten-thousand-fold in one step means transferring a volume too small to pipette accurately; four ten-fold steps arrive at the same place with a workable volume every time.
Each step divides the previous concentration by the factor.
- Concentration at step n
- Cₙ = C₀ ÷ (factor)ⁿ
Where the factor differs from step to step, divide by the product of the factors up to that point.
- With mixed factors
- Cₙ = C₀ ÷ (f₁ × f₂ × … × fₙ)
Once the total volume V per tube is set, the transfer and the diluent follow from it.
- Transfer
- V ÷ factor
- Diluent
- V − (V ÷ factor)
A ten-fold dilution into 1 mL means carrying 100 μL from the previous tube and adding 900 μL of diluent.
Practical notes
- Mix thoroughly at every step. Carrying an unmixed tube forward passes its error into every step after it, and because the errors of a serial dilution multiply, an early one costs the most.
- Change the tip between steps. Concentrated solution clinging to the outside of a tip raises the concentrations downstream above the calculated values.
- When the transfer falls below about 1 μL, a smaller factor over more steps is more accurate. Seven five-fold steps are often easier to handle than five ten-fold ones.
- The volumes in the table make each tube up to the total volume you set. If you need more than that from the last tube, set a larger total — every tube loses what is carried to the next one.
- Substances that adsorb readily — some proteins, oligonucleotides — can come out below the calculated value at the dilute end. Consider low-binding tubes or a carrier.
FAQs
You get the concentration at each step and nothing else, which is convenient when you are checking the series and preparing it later. Fill the total volume in and the transfer and diluent columns appear.
Edit that cell in the Dilution factor column. Changing any one of them switches the shared field above to ‘Custom’, and [Same factor throughout] restores it at any point. An empty cell follows the shared factor.
The final volume. Set it to 1 mL and the transfer and diluent are divided so that each tube comes to 1 mL.
Every tube loses what is carried forward to the next one. Set the total volume with your actual use in mind — if you need 200 μL at each concentration, a total of 500 μL or more is the safe side.
For the same end concentration, more steps means a larger transfer each time, which is more accurate. Against that, more steps means more handling and more chances to accumulate error. The practical answer is usually the fewest steps that keep the transfer at 10 μL or above.
Below a certain size the value switches to scientific notation, such as 1e-5, so that a long run of leading zeros does not have to be counted.