How to Use the Gravel, Mulch & River Rock Calculator
Step 1: How to measure
Measure the length and width of the bed, path or driveway in feet. For L-shaped or irregular areas, break the space into rectangles, calculate each one, and add the results together. For a circle, multiply the radius by itself and by 3.14 to get square feet, then enter that number as the length with a width of 1.
Depth is entered in inches. Typical depths: 2–3 in for decorative mulch, 3 in for pea gravel patios, 4 in for crushed stone driveways (often over a 4 in base), 2–3 in for river rock borders, and 4–6 in for topsoil when establishing a new lawn. If you are topping up existing material, measure what is already there and enter only the extra depth.
Step 2: The exact formula
First find cubic feet: length × width × depth in inches ÷ 12. Divide cubic feet by 27 to get cubic yards — the unit landscape suppliers sell bulk material in. To convert to tons, multiply cubic yards by the material's density.
We use common averages: mulch 0.4 tons/yd³, topsoil 1.1, river rock 1.3, crushed stone 1.35 and pea gravel 1.4. Moisture and stone size change real weight, so confirm with your supplier when ordering by the ton. Mulch and topsoil are bagged by volume (2 cu ft), while stone is bagged by weight (50 lb).
Cubic ft = L ft × W ft × (Depth in ÷ 12) Cubic yd = Cubic ft ÷ 27 Tons = Cubic yd × density
Pro DIY tips
- Bulk delivery is usually cheaper than bags once you need more than about 2 cubic yards.
- Lay landscape fabric under gravel and river rock to stop weeds and keep stone from sinking into soil.
- Install steel or paver edging first so gravel doesn't migrate into your lawn.
- Never pile mulch against tree trunks — keep a 3 inch gap to prevent rot and pests.
- Order 5–10% extra for compaction, especially crushed stone, which settles as it is tamped.
Frequently asked questions
How many bags of mulch are in a cubic yard?
One cubic yard is 27 cubic feet, so it equals 13.5 standard 2 cu ft bags of mulch.
How much does a cubic yard of gravel weigh?
Most gravel weighs 1.3 to 1.5 tons per cubic yard (2,600–3,000 lb). Pea gravel averages about 1.4 tons.
How deep should pea gravel be for a patio?
Use 3 inches of pea gravel over a compacted 4 inch crushed-stone base for a stable walking surface.
How many 50 lb bags of river rock per cubic yard?
At about 1.3 tons per yard, one cubic yard of river rock is roughly 52 bags of 50 lb each.
Is it cheaper to buy gravel in bulk or bags?
Bulk is usually 40–60% cheaper per yard but has a delivery fee. Bags make sense for small jobs under about 1–2 cubic yards.