Calculator
Mulch, soil and gravel calculator
Enter the size of the bed, path or raised bed and how deep the material should be. You get the volume in cubic yards, which is how most suppliers sell bulk material, plus a bag count if you are buying by the bag. The result updates as you type, and nothing leaves your device.
0.5 cubic yards to order
Worked example (shown when scripts are off): a 10 ft by 4 ft bed covered 3 inches deep is 40 square feet times 0.25 feet, which is 10 cubic feet. Add 10 percent and divide by 27 to get about 0.41 cubic yards, which rounds up to 0.5 for the order. A bed of 100 square feet at the same depth needs about 25 cubic feet, close to 1 cubic yard.
Before you order
The numbers assume level ground and an even depth. Measure the real bed, call your local utility locator service before you dig, and ask the supplier how much their truck or bags actually hold.
How the calculator works
The rule is plain volume. Area in square feet, multiplied by depth in inches, divided by 12, gives cubic feet. Divide cubic feet by 27 and you have cubic yards, because a cubic yard is 3 feet by 3 feet by 3 feet. For a circle the area is pi times the radius squared, and the length box is treated as the diameter. The calculator then adds your extra allowance, 10 percent by default, and rounds the order up to the next tenth of a yard.
Worked example
A path 30 feet long and 3 feet wide is 90 square feet. Laid 3 inches deep that is 90 times 3 divided by 12, which is 22.5 cubic feet. With 10 percent extra the order is 24.75 cubic feet, or 0.92 cubic yards, so you would round to 1 cubic yard. A rule of thumb that falls out of the same arithmetic: one cubic yard covers about 108 square feet at 3 inches deep and about 324 square feet at 1 inch.
Choosing a depth
Depth is the number that matters most, and it changes with the material. University extension services commonly suggest a mulch layer of about 2 to 3 inches around trees and shrubs, kept pulled back from trunks and stems. Gravel paths are often laid 2 to 3 inches deep over compacted ground and landscape fabric. Topsoil for a lawn repair is usually a thin layer, while a new raised bed may be filled 8 to 12 inches or more. These are general ranges, so check the advice for your plant, soil and local climate.
Why the extra allowance
Loose material settles, edges are rarely perfectly straight, and a shovel always spills some. A 10 percent allowance is a sensible default for mulch and soil. For gravel on a compacted base you may need slightly more, because it sinks into the ground below. Reduce the allowance if you are filling a tidy box such as a raised bed with straight sides.
Buying by the bag or by the yard
Bags are convenient for small jobs, but the price per cubic foot is usually higher than bulk. Because 27 cubic feet make a cubic yard, a bed that needs more than about 2 yards would take over 25 bags of 2 cubic feet. Bag sizes differ, so check the volume printed on the bag. The tool shows counts for 2 and 3 cubic foot bags. Bulk delivery needs a place to drop it and a way to move it, usually a wheelbarrow.
Limits of the estimate
This tool does not know about slopes, curves cut into a bed, trees that take up space, or edging that holds material in. Material weight depends on type and moisture, so ask the supplier for tons per cubic yard before loading a trailer or a small truck. Mulch that is piled against a trunk can harm a tree, so use the depth guidance rather than extra volume.
Where this comes from
The volume arithmetic is standard geometry and the conversion of 27 cubic feet to a cubic yard. The mulch depth range of about 2 to 3 inches reflects guidance published by US university extension services. Gravel path depth reflects common landscape contractor and supplier guidance. These are general ranges, not a rule for every yard. This page is general information, not professional advice.