Serial Dilution in Microbiology – Definition, Formula, Procedure and Calculator


Definition of Serial Dilution

Serial dilution, as the name suggests, is a series of consecutive mixing that is performed to turn a solid solution into an easy-to-use solution.

  • In simple terms, serial dilution is the process of gradual dilution of a solution with an associated dilution factor.
  • In microbiology, serial dilution is nothing but associated with reducing the concentration of cells in a culture to simplify the solutions.

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serial dilution technique in microbiology

Formula and Calculations for Serial dilution 

  • Serial dilution involves the process of taking a sample and diluting it through a series of standard volumes of sterile diluent, which can be either distilled water or 0.9 % saline solution.
  • After that, a small average volume of each purifier is used to make a series of pouring or dispersing plates.
  • Depending on the relative concentration of cells/organisms in the sample, the size of the stretch is determined. For example, if a water sample is taken from a very polluted environment, the dilution factor is increased. On the other hand, for a less contaminated sample, a low dilution factor might be sufficient.
  • Serial two-fold and ten-fold dilutions are commonly used to titer antibodies or prepare diluted analytes in the laboratory.
  • The dilution factor in serial dilution can be determined either by an individual test tube or can be counted as a complete filtering element throughout the series.
  • The formula for the dilution factor of each tube is –
Formula of dilution factor
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After the first tube, each tube is cleaned of the previous mixing tube.

  • Now, for the total dilution factor,

Total dilution factor for the second tube = dilution of first tube × dilution of the second tube.


Example :

For the first tube, dilution factor = 10-1 (1 ml added to 9 ml)

For the second tube, dilution factor = 10-1 (1ml added to 9 ml)

Total dilution factor = previous dilution × dilution of next tube

= total dilution of 10-1 × 10-1 = 10-2


Top 5 Online serial dilution calculator

Here top 5 online serial dilution calculators we are going to provide you for easy calculations. These calculators may help you to calculate serial dilution.

  1. AAT Bioquest, Inc. (
  2. Merck (
  3. Omni Calculator (
  4. Endmemo (
  5. Handymath (


Procedure of Serial dilution

The following is a ten-step purification process for a 10-6. purification factor.

  • The sample/culture is taken from a test tube and six test tubes, each containing 9 ml of sterile diluent, which can be pure water or 0.9% saline.
  • A sterile pipette is taken.
  • 1 ml of a well-mixed sample/culture is drawn into the pipette.
  • The sample was added to the first tube to form a total volume of 10 ml. This provides an initial dilution of 10-1.
  • Dilution is thoroughly mixed by removing and filling the pipette several times.
  • The pipette tip is discarded, and a new pipe tip is inserted into the pipette.
  • Now, 1 ml of mixture is taken from the 10-1
  • Dilution and poured into a second tube.
  • The second tube now has a total dilution factor of 10-2.
  • The same process is repeated with the remaining tube, taking 1 ml from the previous tube and adding to the next 9 ml diluents.
  • As six tubes are used, the final reduction of germs/cells will be 10-6 (1 in 1,000,000).


Uses of Serial Dilution method –

Serial dilution is done in most experimental sciences such as biochemistry, pharmacology, physics, and homeopathy.

  • Serial dilution is used in microbiology to measure the concentration or number of cells/organisms in a sample to obtain an incubated plate with colonial numbers easily.
  • In biochemistry, serial dilution is used to obtain the desired combination of reagents and chemicals from high concentrations.
  • In medical laboratories, serial dilution is performed to obtain the necessary chemical and chemical diagnoses as this method works better than each dilution.
  • In homeopathy, homeopathic dilutions are used when the substance is diluted with water or distilled. It is believed that there is a purification that enhances the power of the purified substance by making its vital energy.


Limitations of Serial Dilution

Although serial dilution is a useful method in laboratories, it faces some challenges. Some of which are:

  • An error occurred while distributing the sample, and the transmission inaccuracy leads to more accurate and less accurate transmission. This results in very high purity with very little precision and less precision.
  • Because serial processing is done in a non-invasive manner, it requires more time determined by the efficiency of the method.
  • Purification of the product allows only the reduction of germs/cells but not the separation of germs/cells as in other techniques such as flow cytometry.
  • This method also requires highly trained microbiologists and specialists in aseptic techniques.


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