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Geometric Mean Calculator for Wastewater

Interactive spreadsheet to compute the geometric mean on a set of numbers to assist with completion of discharge monitoring reports (DMR) for domestic wastewater facilities.


  1. Open the Geometric Mean Calculator spreadsheet.
  2. Determine the frequency of bacterial sampling required in your permit.
  3. Enter lab data (bacteria sampling results) in the appropriate cells on the sheet.
  4. If a sample result is zero, enter a 1 in that cell.
  5. The geometric mean will be calculated automatically.
  6. Enter the geometric mean result onto your DMR.

Note: For permits requiring once-per-month sampling, the lab data IS the geometric mean to enter in the DMR.

The formula for calculating geometric mean is the nth root of the product of all monitoring data.
(N1 * N2 * N3...)(1/Count)

Download Spreadsheet:

Please call the Small Business and Local Government Assistance (SBLGA) section of the TCEQ at (800) 447-2827 if you need help using this tool.

Download the Geometric Mean Calculator Spreadsheet Microsoft Excel


  • CFU—colony forming units per 100 milliliters
  • DMR—discharge monitoring report
  • MPN—most probable number per 100 milliliters

Small Business and Local Government Assistance

TCEQ's Small Business and Local Government Assistance section offers free, confidential help to small businesses and local governments working to follow state environmental regulations. Call us at (800) 447-2827 or visit our webpage at