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My back yard is 80 ft x 110 ft. I want to spread a layer of top soil 6 inches deep on it. How much dirt will I have to order? Can you give me a mathematical formula that I can use, please?

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My first question, is "why?". What's wrong with the soil you have now? If it's clay or sand, then you're in danger of creating a perched water table at the native soil/new topsoil interface due to differences in soil pore sizes. Unless it's full of rocks, it's almost always better to work with native soil than to add additional soil to the site.

One important note: If you have one or more trees in your yard, burying their feeder roots and the trees' root flares under six inches of soil is very likely to kill them.

But, since you asked for a formula, this is the one we've used for years in the trade:

1 cubic yard of soil or mulch will cover 100 square feet 3 inches deep (non-compacted).

Your yard is 8800 sq feet, so you'd need 88 yards of topsoil to cover the entire yard with three inches of topsoil, or 170 yards +/- to cover it six inches deep. Large dump trucks typically can haul 20 cubic yards, so you're looking at 8 large dump trucks full of topsoil.

Note that whoever is doing the spreading of the topsoil is likely to use one or more skidsteers, which will compact the new soil quite a bit. This means that the final depth will be more like three to four inches, not six inches.

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  • Excellent that you noted that delivered soil gets compacted. That sure surprised me for one job!
    – kevinskio
    Commented Sep 13, 2023 at 20:01

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