Mulch and Soil Calculator

Mulch and soil, like concrete, are sold by volume, so getting the right amount for a garden bed comes down to the same basic math: length times width times depth, converted into units you can actually buy.

This calculator multiplies your bed's length and width by your desired depth to get a volume in cubic feet, then converts that to cubic yards, since bulk mulch and soil from a landscaping supplier are typically sold and delivered by the yard. For smaller projects, it also converts that volume into a count of standard 2-cubic-foot bags, the size most garden centers and hardware stores sell mulch and topsoil in.

Depth matters more than people often expect. A thin 1-inch layer barely suppresses weeds and dries out quickly, while most landscaping guides recommend 2 to 4 inches of mulch for weed control and moisture retention without smothering plant roots or stems. Garden soil and compost mixed into an existing bed is often applied a bit deeper, especially when amending poor soil, so the right depth really depends on what you're doing: topping off mulch versus building up a new raised bed calls for different amounts.

One practical note: if you're mulching around existing plants, subtract their footprint loosely from your bed dimensions, since mulch shouldn't be piled directly against stems or trunks (a common mistake called "volcano mulching" that can trap moisture against bark and encourage rot). And when ordering bulk material, it's common to round up slightly, since settling and uneven ground mean you'll often use a bit more than the flat geometric calculation suggests.