Dilution Series Calculator
A serial dilution reduces sample concentration in a systematic stepwise fashion. At each step, the concentration is divided by the dilution factor: C(n) = C(0) / (DF)^n, where C(0) is the initial concentration, DF is the dilution factor (e.g., 10 for a 1:10 dilution), and n is the step number. This calculator generates the concentration at every step for up to 12 steps, making it straightforward to plan standard curves, dose-response experiments, or bacterial plate counts. Enter your initial concentration, dilution factor, and number of steps.
Serial dilution formula
C(n) = C(0) / (dilution factor)^n
where n = step number (1, 2, 3, ...)
C(0) = initial undiluted concentration
Example: C(0) = 1,000 ug/mL, DF = 10: Step 1 = 100 ug/mL, Step 2 = 10 ug/mL, Step 3 = 1 ug/mL, Step 4 = 0.1 ug/mL, Step 5 = 0.01 ug/mL, Step 6 = 0.001 ug/mL.
Preparing dilutions correctly
- For a 1:10 dilution: add 100 uL of sample to 900 uL of buffer (total 1,000 uL).
- Always use a fresh tip or pipette between steps to avoid carryover contamination.
- Vortex or mix thoroughly at each step before transferring to the next tube.
- For ELISA standard curves, use the same diluent buffer as the sample matrix.
- Label tubes clearly with the step number and expected concentration for traceability.
Frequently asked questions
What is a serial dilution?
A serial dilution is a sequence of successive dilutions where each step uses the same dilution factor. If the dilution factor is 10 and you make 6 steps, the concentrations are C, C/10, C/100, C/1,000, C/10,000, C/100,000, C/1,000,000. Serial dilutions are used to create standard curves, reduce sample concentration to a measurable range, and count bacteria by plating.
What is the formula for each dilution step?
Concentration at step n = initial concentration / (dilution factor)^n. For a 1:10 serial dilution starting at 1 mg/mL: step 1 = 0.1 mg/mL, step 2 = 0.01 mg/mL, step 3 = 0.001 mg/mL, and so on.
What is the difference between dilution factor and fold dilution?
They are the same concept. A 1:10 dilution means 1 part sample in 10 parts total (sample plus diluent). The dilution factor is 10 (concentration is divided by 10 at each step). A 1:2 dilution (e.g., mixing equal volumes of sample and buffer) gives a dilution factor of 2.
How many steps should I use for a standard curve?
For enzyme-linked immunosorbent assay (ELISA) standard curves, 7-12 points are typical. For drug dose-response curves (IC50), 8-10 points spanning 3-4 orders of magnitude are common. For plate count serial dilutions, typically 6-8 steps of 1:10 are made.
Can I use a non-integer dilution factor?
Yes. This calculator accepts any dilution factor greater than 1. For example, a factor of 2.5 or 3 is common in some bioassay protocols. Ensure you are consistent: always add the same volume ratio (e.g., 1 mL sample to 1.5 mL buffer for a factor of 2.5).
Official sources
- NIH/NCBI: Concentration and dilution calculations in biochemistry.
- FDA BAM: FDA Bacteriological Analytical Manual (serial dilution methods).
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.