Mulch Volume Calculator

Volume Formula

Mulch volume is length times width times depth. To get cubic feet, divide the depth in inches by 12 to convert to feet, then multiply by the area. A 20 x 10 ft bed at 3 inches deep is 200 sq ft times 0.25 ft, or 50 cubic feet. To convert cubic feet to cubic yards, divide by 27. So 50 cubic feet is 1.85 cubic yards. The shortcut formula straight from square footage is Area times Depth in inches divided by 324, which combines both conversions into one step. The calculator returns cubic feet, cubic yards, cubic meters, and bag count together.

Multi-Shape Volume

A yard with mixed bed shapes needs shape-by-shape volume. Calculate each rectangle, circle, and triangle separately, then add the cubic feet together. A rectangle uses length times width. A circle uses pi times radius squared. A triangle uses half base times height. Multiply each area by the same depth and sum the volumes. Divide the total cubic feet by 27 for cubic yards. This method, used by the National Association of Landscape Professionals (NALP), keeps the estimate accurate across a complex landscape with several bed shapes.

Volume per Square Foot

Mulch volume per square foot depends only on depth. At 3 inches deep you need 0.25 cubic feet per square foot. At 2 inches it is 0.167 cubic feet, and at 4 inches it is 0.333 cubic feet. Multiply your square footage by this factor to get total cubic feet. The Mulch and Soil Council (MSC) bases all bag labeling on cubic feet, so this per-foot figure tells you exactly how many 2 cubic foot bags to buy. One cubic yard of mulch always equals 27 cubic feet regardless of material or shape.

Why does volume use 27 and 324?

The number 27 is the cubic feet in a cubic yard, since a yard is 3 feet and 3 x 3 x 3 equals 27. The number 324 is 27 times 12, which lets you go straight from square feet and depth in inches to cubic yards in one step. Both constants come from unit conversions, not from the mulch itself. Using them avoids the common error of mixing inches and feet.

How do I convert volume to metric?

To convert cubic feet to cubic meters, multiply by 0.0283. A 50 cubic foot bed is 1.42 cubic meters. European bagged mulch is sold in liters, where 1 cubic foot equals 28.3 liters. The calculator shows cubic meters alongside cubic feet and yards so you can order from suppliers that use either system.

Volume for Circles and Triangles

Not every bed is a rectangle, so the volume formula changes with the shape. For a circle, the area is pi times the radius squared, where the radius is half the diameter. An 8 ft circle has a 4 ft radius and a 50.3 sq ft area. For a triangle, the area is half the base times the height. Once you have the area in square feet, the depth step is the same for every shape: multiply area by depth in inches and divide by 324 for cubic yards.

Mixed-shape yards add the volumes together. Calculate each rectangle, circle, and triangle separately, convert each to cubic feet, and sum them. A yard with a 200 sq ft rectangle, a 50 sq ft circle, and a 30 sq ft triangle totals 280 sq ft, or 2.59 cubic yards at 3 inches. This shape-by-shape method, standard for the National Association of Landscape Professionals (NALP), keeps the volume accurate across a complex landscape. Always add the 10 percent buffer and round bags up before ordering.

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