How Much Gravel, Soil, or Concrete Do You Need? A Simple Guide
Whether you're laying a gravel driveway, filling raised beds with topsoil, pouring a concrete slab or spreading mulch, the first question is always the same: how much do I actually need? Order too little and the job stalls halfway; order too much and you've paid for material that sits in a pile. The good news is that a single, simple idea covers almost every bulk material — and once you understand it, the calculators do the arithmetic for you.
The one formula behind every estimate
Every bulk material — gravel, sand, soil, mulch, asphalt, concrete — is sold by volume, and volume is just area × depth. Measure the area you're covering, decide how deep the layer should be, multiply them together, and you have the volume. That's the entire secret. A 20-foot by 10-foot area is 200 square feet; cover it 3 inches deep and you have 200 × 0.25 = 50 cubic feet of material.
The only thing that trips people up is units. Areas are measured in feet, but depths are usually just a few inches, so you have to convert the depth to feet first (divide inches by 12) before multiplying. Our material calculators — the gravel, topsoil, sand, mulch, asphalt and concrete calculators — all handle that conversion automatically, so you enter feet and inches naturally and they return the volume.
Cubic yards, tons and bags: the units you buy in
Cubic feet is the raw volume, but suppliers rarely sell in cubic feet. Bulk material is usually priced by the cubic yard (there are 27 cubic feet in a cubic yard), and heavy aggregates like gravel, sand and asphalt are often sold by the ton. Converting volume to weight needs the material's density: gravel is roughly 1.4 tons per cubic yard, sand about 1.35, screened topsoil around 1.1, and compacted asphalt close to 2 tons per cubic yard. Those figures vary with moisture and exact composition, which is why every estimate is an approximation you confirm with your supplier.
Bagged materials work differently. Concrete comes in bags rated by yield — an 80-pound bag makes about 0.6 cubic feet, a 60-pound bag about 0.45 — so a cubic yard takes roughly 45 or 60 bags respectively. Mulch is sold in 2- or 3-cubic-foot bags, so a cubic yard is about 13.5 of the small bags. Each of our calculators shows the figure that matches how that material is actually sold: tons for aggregates, bag counts for concrete and mulch, and cubic yards throughout for bulk orders.
How deep should each material go?
Depth is where projects differ, and getting it right matters more than the area. As a rough guide: a gravel walkway needs about 2 inches, a gravel driveway 3–4 inches over a base; paver bedding sand is about 1 inch; new-lawn topsoil is 3–4 inches while raised beds want 6–12; mulch works best at 2–3 inches (deeper smothers plants); a residential concrete slab is typically 4 inches, and an asphalt driveway 2–3 inches of hot mix over a compacted base. When in doubt, a slightly deeper layer of the cheaper materials is forgiving, but concrete and asphalt thickness should follow local standards for the load they'll carry.
Odd shapes and round areas
Not every project is a neat rectangle. For a circular patio, fire-pit surround or round planter, the area is π × radius² — and each of our calculators has a circle mode where you just enter the diameter. For an irregular shape, the easiest approach is to break it into rectangles and circles, estimate each piece, and add them up. It's better to slightly over-estimate an awkward area than to leave a gap you can't fill from the same batch.
How much extra to order
Always add a margin. Ground is never perfectly level, loose material compacts once it settles, edges are ragged, and some material is simply lost in handling. A 10% extra allowance is a sensible default for most jobs, which is why our calculators add it by default (you can switch it off for an exact volume). For concrete especially, running short mid-pour is a real problem — a cold joint where fresh concrete meets set concrete is a weak point — so err on the generous side. Left-over gravel, soil or mulch is easy to use elsewhere; a half-finished pour is not.
Put it all together and the workflow is quick: measure the area, pick a depth, let the calculator convert to cubic yards and tons or bags, keep the 10% cushion, and take that figure to your supplier. If you're also building steps or buying lumber for edging or forms, the stair calculator and board foot calculator round out the same project.
Common questions
The recurring theme across every material is the same: estimate the volume from area and depth, convert to the unit your supplier sells in, and add a little extra. Densities and bag yields are approximate, so treat the numbers as a well-informed starting point rather than an exact science, and confirm the final order with whoever you're buying from.