Compost Calculator

Top-Dressing Depth

Lawn top-dressing with compost should be a quarter to half inch deep. Penn State Extension recommends 0.25 to 0.5 inch for established lawns. Going above half an inch smothers the grass crowns and blocks sunlight to the turf. At a quarter inch, 1,000 square feet needs 0.77 cubic yards, about 21 cubic feet or 10 bags of 2 cubic feet. Top-dress right after core aerating so the compost works into the holes and reaches the root zone. The formula is square feet times depth in inches divided by 12, then divided by 27 for cubic yards.

Mix-Into-Soil Ratios

To amend a planting bed, mix 1 to 3 inches of compost into the top 6 to 8 inches of soil before planting. A 100 square foot bed at 2 inches needs about 0.62 cubic yards, or 17 bags of 1 cubic foot. For poor or heavy clay soil, use the deeper 3 inch rate. For decent soil, 1 to 2 inches is enough. Compost weighs about 50 pounds per cubic foot, so a cubic yard weighs around 1,350 pounds. The calculator returns cubic yards, cubic feet, bag count, and weight for both top-dressing and amendment depths.

Sheet Composting Layers

Sheet composting builds soil right on the bed without a separate pile. Alternate layers of brown carbon material like shredded leaves and cardboard with green nitrogen material like grass clippings and kitchen scraps. Make each layer 2 to 4 inches thick and finish with a compost cap on top. The layers break down in place over 3 to 6 months, smothering weeds while feeding the soil. Also called lasagna gardening, this method turns a patch of lawn into a planting bed over one season. Calculate the finished compost cap with the same depth formula the calculator uses.

How much compost per 1,000 sq ft of lawn?

Top-dress about 1 cubic yard of compost per 1,000 square feet after core aerating, which works out to roughly a third of an inch. For a lighter quarter inch application, you need only 0.77 cubic yards per 1,000 square feet. Spread the compost evenly with a rake or a broadcast spreader and water it in. Never exceed half an inch at once or the grass suffers.

Is compost the same as mulch?

Compost and mulch serve different roles. Compost is decomposed organic matter that feeds the soil, used thin as a top-dress or mixed in as an amendment. Mulch is a surface layer at 2 to 3 inches that blocks weeds and holds moisture. Compost can act as a thin mulch, but it breaks down fast and does not suppress weeds as well as wood mulch. Many gardeners layer compost under wood mulch to get both feeding and weed control.

When and How to Top-Dress a Lawn

Top-dress a lawn in the growing season, in spring or early fall, so the grass recovers quickly. Mow first, then core aerate to open the soil. Spread a quarter to half inch of finished compost with a shovel or a broadcast spreader. Rake or drag it into the aeration holes so it reaches the root zone instead of sitting on the blades. Water lightly to settle the compost. The grass grows through the thin layer within a week or two.

Top-dressing builds soil over time without disturbing the lawn. The compost feeds the soil microbes, improves drainage, and slowly levels minor low spots. Repeat once or twice a year for a few seasons to transform thin, compacted turf into healthy grass. Never bury the grass: more than half an inch at once blocks sunlight and smothers the crowns. Use only finished, screened compost so you do not introduce weed seeds or clumps that scalp under the mower.

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