How to Calculate Serial Dilutions

by Allan Robinson

A dilution is a reduction in the concentration of a solution. A serial dilution is a series of repeated dilutions that provides a geometric dilution of the original solution. This is commonly performed in experiments that involve concentration curves on a logarithmic scale. Serial dilutions are used extensively in biochemistry and microbiology.

Fill test tube A with 10 mL of the solution and fill test tube B with 9 mL of a buffer to dilute the original solution. The buffer is typically water, but it also can be other liquids, depending on the solution in test tube A.

Draw 1 mL of the solution in test tube A with the pipette, transfer it to test tube B and mix the contents of test tube B. The solution in test B is 10 times more dilute than the solution in test tube A.

Fill test tube C with 9 mL of buffer. Transfer 1 mL of the solution in test tube B to test tube C and mix thoroughly. The solution in test tube C is 10 times more dilute than the solution in test tube B.

Examine the effects of serial dilution. The solution in test tube C is 10 times more dilute that the solution in test tube B, which is 10 times more dilute than the solution in test tube A. The solution in test tube C is, therefore, 10 x 10 = 100 times more dilute than the solution in test tube A.

Calculate the total dilution in a serial dilution. We can generalize the results of Step 4 by saying that the total dilution ratio Dt is given by the equation Dt = D1 x D2 x D3 x ... x Dn, where Di is the dilution ratio of the ith dilution.

Things You Will Need

  • Three or more test tubes
  • Buffer
  • Pipette
  • Solution

About the Author

Allan Robinson has written numerous articles for various health and fitness sites. Robinson also has 15 years of experience as a software engineer and has extensive accreditation in software engineering. He holds a bachelor's degree with majors in biology and mathematics.