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:

• a custom compost amendment rate, which is the number of inches of compost to be layered over the site surface and mixed in
• quantity of compost needed in cubic yards
• quantity of site soil to be stockpiled in cubic yards
• quantity 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.