How we calculate material quantities and purchases.

1. Find the area

For a rectangle, multiply length by width. For a triangle, multiply base by height and divide by 2. For a circle, square half its diameter and multiply by π. You can also enter an area measured elsewhere. We convert feet and inches or metric measurements to square feet, then add the areas together. For an irregular bed, break it into simple shapes or enter your own measured area; the result is only as accurate as those measurements.

2. Add depth and extra

For a new layer or fill, use your target depth. For a top-up, subtract the current depth from your target, with a floor of zero. Enter inches, or centimeters in metric mode; we convert to inches before calculating. Divide added inches by 12 to get feet. The mulch tool applies one depth to the combined area; the raised bed soil tool calculates each bed at its own added depth, then adds the volumes. The extra percentage is a user-controlled allowance. It is an estimate, not a universal requirement.

For 104 ft² at 3 in on bare beds: 104 × 3 ÷ 12 = 26 ft³. With 10% extra: 26 × 1.10 = 28.6 ft³. Divide by 27 for cubic yards: 1.059 yd³. If the beds already have 2 in of mulch and the target is 3 in, calculate only the added 1 in.

Already know the mulch volume?

Use the known-volume entry to start with cubic yards or cubic feet instead of bed dimensions. Multiply cubic yards by 27 to get cubic feet. Apply your extra allowance once, then round to whole bags and each supplier’s order rules. This mode starts at 0% extra; keep it there if the entered volume already includes an allowance. We do not infer a bed area or depth from volume alone.

3. Round to what you can actually buy

Divide the needed cubic feet by the size printed on the bag. Always round up to a whole bag. With 2 ft³ bags, 28.6 ÷ 2 = 14.3, so the shopping list says 15 bags.

For bulk, apply the supplier's minimum order and increment. If a supplier sells by the half yard, 1.059 yd³ rounds up to 1.5 yd³. A higher minimum could raise that purchase amount.

4. Compare your costs

Bag cost is whole bags × price per bag. For each bulk supplier you enter, we apply that supplier's minimum and increment, then calculate orderable cubic yards × price per cubic yard + delivery. We compare only options with prices entered; a missing price is never treated as free. The difference uses these purchase totals, including unused material caused by rounding. Prices are entered by you and are not fetched or stored by our site. Taxes, pickup costs, and other fees are not included unless you include them in your entered prices.

Gravel orders by volume or weight

Start the gravel calculator with dimensions in feet and inches, a known volume in cubic yards, or a known weight in US short tons. A US short ton is 2,000 lb; it is different from a metric tonne. Dimensions give geometric volume for sections with one material and depth.

Short tons = cubic yards × supplier-confirmed short tons per cubic yard. In the other direction, cubic yards = short tons ÷ supplier-confirmed short tons per cubic yard. A known weight requires that density to calculate volume. Without density, dimensions and known-volume entries produce a volume-only estimate; a ton-priced quote cannot be compared.

We apply your extra allowance once to the starting quantity, before supplier rounding. For example, 2 short tons with 10% extra becomes 2.2 short tons; at a supplier-confirmed density of 1.4 short tons/yd³, that is about 1.57 yd³. If your known volume or weight already includes extra, enter 0% to avoid adding it again.

Each quote uses its own units, minimum order and increment. Delivered cost is the rounded order quantity × price per cubic yard or short ton + delivery. Run separate estimates for different materials or layer depths. See the gravel yards-to-tons and tons-to-yards guide for worked purchase examples.

Where estimates can differ from reality

Curved edges, product labels, compaction, settling, slopes, and supplier measurement practices can affect the amount used. Measure carefully and confirm each supplier's rules before ordering. The calculator is intended for planning a purchase, not a guaranteed installed volume.

Try the mulch calculator, plan raised bed soil, or estimate a gravel order.