Caution: Please read the information on this page before downloading the MIDS calculator
Caution: The default infiltration rate for SM soils is 0.30 inches per hour in the calculator. Recently this value was changed in the Manual to 0.45 inches per hour. If you have SM soils at your site do not use the default value in the calculator but instead input the infiltration rate as 0.45 inches per hour.
Caution: Volume and pollutant reductions calculated with the MIDS calculator will be incorrect if BMPs do not meet the following criteria
  • Volume and pollutant reductions given in the MIDS calculator are based on the assumption that the BMP is properly designed, constructed and maintained. Guidance and recommendations for design, construction and maintenance are contained within the individual BMP sections of this Manual. You can find lists of relevant web pages at the following links.
  • BMPs must be designed and constructed in accordance with the Construction Stormwater General Permit (CSW permit). Requirements of the CSW permit are highlighted in red throughout the various sections of this Manual. It is important to note that volume reduction BMPs need at least three feet of separation to the seasonally saturated soils to be eligible under the CSW permit to receive credit for volume reduction. The pollutant removal credit is not valid for undersized or oversized practices.
  • The MIDS calculator does not require sizing criteria for BMPs that do not achieve volume reductions (ponds, wetlands, sand filters). The pollutant removal credit in the calculator assumes these BMPs are properly sized per recommendations in this Manual.

We anticipate enhancements to the Manual and calculator when additional resources allow. Below are two important examples.

  • Volume credits for evapotranspiration and interception by trees are not included in the calculator, although these credits are discussed in the Manual.
  • There will be individual pages for each BMP in the calculator that explain requirements and inputs for the calculator. An example exists for bioretention. We anticipate these pages will all be available by early spring.

We welcome comments and suggestions on the calculator. Please send comments to Anne Gelbmann at We will compile comments and, if resources allow, incorporate suggestions into future versions of the calculator.

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