Mulch and gravel are sold in two completely different units depending on where you buy them. Hardware stores sell bags measured in cubic feet (typically 2 cubic feet per bag). Landscape supply yards sell by the cubic yard, delivered in a dump truck. Most homeowners have no intuitive sense of how a cubic yard translates to their garden bed, which leads to either over-ordering (expensive, and you are stuck with a pile of gravel in your driveway) or under-ordering (another delivery fee).
This calculator bridges that gap. Enter your bed dimensions and desired depth, and it converts to both cubic yards (for bulk delivery) and bag count (for retail purchase). It also shows weight estimates, because a cubic yard of river rock weighs about 2,700 pounds, roughly a ton and a half, which matters if you are hauling it yourself.
The cost breakpoint between bags and bulk is typically around 3 to 4 cubic yards. Below that, bags are more convenient. Above that, bulk delivery is significantly cheaper per cubic yard and saves hours of loading bags into your car.
The mulch calculator uses a simple volume formula: length times width times depth (in feet) equals cubic feet. Since depth is typically measured in inches, the calculator divides by 12 to convert to feet first. The result in cubic feet is then divided by 27 to get cubic yards (since 1 cubic yard equals 27 cubic feet).
For bag counts, the total cubic feet is divided by the bag size (standard 2 cubic foot bags for mulch, 0.5 cubic foot bags for pea gravel and decorative stone). Weight estimates use material-specific densities: hardwood mulch weighs about 400 to 600 pounds per cubic yard, gravel about 2,800 pounds, and river rock about 2,700 pounds.
A 10 percent overage is not included by default for mulch (unlike concrete) because mulch settles by 10 to 15 percent naturally over the first few weeks. Ordering the calculated amount gives you the right coverage after settling.
Use this calculator when planning any mulch or gravel installation: garden bed mulching in spring, gravel driveways, pea gravel patios, river rock borders, or playground surfacing. For irregularly shaped beds (curved borders, kidney-shaped planting areas), measure the longest and widest points and use 75 percent of the rectangular calculation as a good approximation. For very precise odd shapes, divide the area into smaller rectangles and circles, calculate each, and sum the results.