# About the Compost Calculator

The compost calculator can be used to estimate the amount and depth of compost (or any organic material) to amend an existing topsoil to satisfy a need for organic content (% organic by weight) in a planting substrate. The yellow boxes are for the variables in generating the results in the green boxes. This calculator can be used by designers to produce maximum estimated quantities of compost by assuming a zero organic content of existing topsoil. Contractors using topsoil and compost of known organic content might use the calculator to estimate the actual amount of compost required to produce the specified organic backfill. When an in-place soil is to be amended, the Calculator can estimate the depth in inches of the organic material required to amend soil twelve inches below the surface. If in-place soil is to be amended to a depth of only six inches, for example, then the estimated depth of compost can be reduced by 50% as the relationship is linear. An example calculation is shown in the Calculator below. Users should replace the example variables (yellow boxes) with appropriate numbers as needed prior to running a computation.

The Compost Calculator can be a useful tool for estimating compost quantities but any potential users are encouraged to cross check any specific estimates with other methods before relying on the accuracy of the tool. Any comments related to the accuracy or usefulness of the Compost Calculator are welcome and can be sent to the developer at Steve.Russell@VirginiaDOT.org.

## Compost Calculator

(1) Equal to % Organic Content of Backfill minus % Organic Content of Existing Topsoil

(2) Product of the bulk density of soil, the wt. of water: 62.4 lbs/C.F. (0.0312 T/C.F.) & sq. ft. in an acre.

(3) Product of the bulk density of the compost & the wt. of water: 62.4 lbs/C.F. (0.8424 T/C.Y.)

(4) Product of the bulk density of the soil & the wt. of water (0.8424 T.)

(5) Product of the tons of compost required per ton of soil & the wt. of a C.Y. of soil.

(6) Product of the tons of compost required per ton of soil & the wt. of a C.Y. of compost.

(7) Product of the tons of compost required per ton of soil & tons of soil per ac. ft.

(8) Tons of compost req. per ac. ft. of soil divided by wt. of a C.Y. of the compost

(9) C.F. of compost req. per ac. ft. divided by 43560 S.F. per ac. and the 12" depth of a C.F.

In calculating the weight of an acre-foot of soil, soil is compared to water in weight. When a soil has a density of 1.32, it means the soil weighs 1.32 times more than the equivalent amount of water.

For more information on soil partical density, go to http://www.westernlaboratories.com/