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Compost and topsoil calculator

Use the compost and topsoil calculator for site development planning.

Our compost and topsoil calculator can help you determine the compost or topsoil needs for site development projects. This includes completing the permitting application for meeting the post-construction soil standard.

Use it to calculate:

  • Custom compost amendment rate
    • This is the number of inches of compost to be layered over the site surface and mixed in
  • Amount of compost needed (in cubic yards)
  • Amount of site soil to be stockpiled (in cubic yards)
  • Amount of imported topsoil needed (in cubic yards)

STEP 1

Visit the King County Post-Construction Soil Standard page to understand code requirements and soil management options.

STEP 2

Determine which soil management option(s) are needed for each area marked on your project site map.

STEP 3

Choose Turf or Planting beds and determine Amendment rate of compost needed.

For soil treatment options that involve adding compost to the soil, you need to choose either the pre-approved amendment rate of application or a custom amendment rate. A custom amendment rate will be lower than the pre-approved rate for most sites. To calculate a custom amendment rate, you will need to enter information from laboratory tests of the site soil and specified compost products.

Are you performing a turf or planting application? (choose one)

Pre-approved or Custom compost amendment rate? (choose one)

STEP 4

For each option needed, enter the following into the table below

  • Identification of site area(s) marked on site map (for example, A, B, C)
  • Total square footage for all areas on map where the options will be implemented
Soil management options Areas on site map using this option(A, B, C) Total square footage for all areasIn thousands, no commas (enter 4,525 square feet as 4525)
Option 1
Leave native soil undisturbed		 Not applicable Not applicable
Option 2
Amend existing soil in-place
Option 3
Import topsoil mix
Option 4
Disturbed Soil - stockpile, reapply and amend

STEP 5

Enter the results of the calculations from the table above to your Soil Management Plan, and attach a print-out of the calculation results to the plan.

Note that separate calculation sheets are needed for turf and planting beds.

Submit your completed plan to Department of Local Services, Permitting Division as part of the permitting process.

The Department of Local Services's reviewers will also use the calculator to verify the compost and/or soil quantities are correct.

Related topics

Post Construction Soil Standard

Learn how to meet the post-construction soil standard

Clearing & grading permit

Find info on the permit process

CompostWise

Learn about our program to support greater use of compost by public agencies

Organics summits

View recordings from our regional organics summits
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