Updated October 14, 2026 · Methods & editorial approach
Start with the area you will cover
Measure the actual bed or path, not the whole property. Use a tape measure and write down each measurement in the same unit. Measure length and width in feet for US inputs, or meters for metric inputs. Enter the finished material depth separately in inches or centimeters.
Break awkward shapes into simple ones
Split an L-shaped bed into two rectangles that do not overlap. Measure each rectangle and add it as its own area in the calculator. For a round bed, measure straight through the center from edge to edge: that is its diameter, not its radius. For a triangle, multiply its base by its perpendicular height and divide by two. Choose Known area and enter that result, using square feet or square meters to match your selected units.
Check depth in several places
For a refresh, estimate the additional depth you need rather than applying the full target depth over existing material. Uneven ground changes the quantity. Take several depth readings and use a representative average for an initial estimate; use separate areas where depths differ substantially.
Keep an allowance separate
Our tools start with a 5% planning allowance. This is an editable example, not a universal installation requirement. Gravel compaction, irregular edges, spillage and delivery increments can change the order. Ask your supplier or installer which allowance is appropriate before buying.
Example: two garden beds
A 12 × 8 ft bed and a 6 × 4 ft bed total 120 square feet. At 3 inches deep, they require 30 cubic feet, or 1.111 cubic yards. A 5% allowance raises the planning amount to 1.167 cubic yards. At 2 cubic feet per bag, round up to 16 bags.
Try the uneven-bed worksheet
In the table, Bed A needs 2 inches while Bed B needs 4 inches. The total is 24 cubic feet. A chosen 5% allowance gives 25.2 cubic feet, or 0.933 cubic yards; 2-cubic-foot bags require 13 whole bags. Adding both areas at one guessed depth would lose the distinction that makes this estimate useful. Enter them as separate rectangles in the calculator.
Exclude a circular space from a larger bed
For a 10-foot-diameter circular bed containing a 4-foot-diameter area that will remain uncovered, subtract the smaller circle: π × (5² − 2²) = about 65.97 square feet. Enter that result as Known area. At 2 inches of additional depth it needs about 0.407 cubic yards before allowance. This describes geometry only; it does not prescribe the correct clearance around a particular tree.
A one-inch error can outweigh your allowance
On 200 square feet, each additional inch changes volume by 200 ÷ 324 = 0.617 cubic yards. At 3 inches, the measured volume is 1.852 cubic yards; at 4 inches it is 2.469 cubic yards, a 33.3% increase. A 5% allowance on the 3-inch estimate adds only 0.093 cubic yards. If you are unsure of the depth, measure again or calculate both plausible depths; a small allowance cannot correct an unknown layer thickness. These are alternative measurement scenarios, not a statistical confidence interval.
Check the itemized estimate before buying
After calculating, use the area-by-area table to compare every section with your sketch. It lists the entered dimensions, additional depth, calculated area and measured cubic yards. Check that circular measurements are diameters, that no two sections overlap, and that each depth is the added layer rather than the total existing fill. The summary adds allowance once and shows the whole-bag surplus for mulch. If you edit an input, the breakdown disappears until you calculate again so you do not order from an old result.
Keep one consistent measurement record
Record each section on a separate line: section name, shape, dimensions with units, existing depth, intended depth and additional depth. For the uneven-bed example above, label the rows Bed A and Bed B on your sketch and match them to Area 1 and Area 2 in the tool. Print the calculated estimate to take to the supplier. Have them confirm the product, loose versus finished quantity, sales unit, minimum quantity, increment and delivery charge before placing an order.
| Section | Area | Additional depth | Measured volume |
|---|---|---|---|
| Bed A: 12 × 8 ft | 96 ft² | 2 inches | 16 ft³ |
| Bed B: 6 × 4 ft | 24 ft² | 4 inches | 8 ft³ |
| Combined | 120 ft² | Different by section | 24 ft³ / 0.889 yd³ |
Before you order
- Sketch and name each non-overlapping section before measuring.
- Record length, width or diameter with the unit beside every number.
- Subtract paving, trunks and other areas you will not cover.
- Record additional depth separately for each section.
- Confirm the final volume, density if needed, and delivery arrangement with the supplier.
Put your measurements to work.
Calculate volume, adjust your allowance and save a link to your estimate.
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