To work out how much gravel you need, multiply the area (length × width in feet) by the depth in feet to get cubic feet, divide by 27 for cubic yards, then multiply by about 1.4 for tons. Add 10% for waste. A 200-square-foot area at 4 inches deep needs roughly 2.5 cubic yards, or 3.5 tons.
The formula to calculate gravel
Every gravel estimate comes down to one formula: volume = area × depth. The only work is getting the units to agree and then converting the volume into the cubic yards or tons a supplier uses. Here is the whole method:
- Measure the area in feet. Length × width for a rectangle; π × radius² for a circle. Break L-shapes into rectangles and add them.
- Turn depth into feet. Divide inches by 12. Two inches is 0.167 ft, four inches is 0.333 ft.
- Multiply to get cubic feet, then divide by 27 to get cubic yards (there are 27 cubic feet in a cubic yard).
- Convert to tons by multiplying cubic yards by the stone’s density — about 1.4 for standard gravel, 1.35 for pea gravel.
- Add a waste allowance, usually 10%, for settling, spillage and uneven ground.
Worked example. A 15 ft × 10 ft patio base at 3 inches: area = 150 sq ft; depth = 0.25 ft; volume = 37.5 cu ft ÷ 27 = 1.39 cubic yards; × 1.4 = 1.94 tons; + 10% = about 1.5 cubic yards or 2.1 tons.
How much gravel do I need by area?
The chart below shows how much standard gravel common areas take at two typical depths. It already includes a 10% waste allowance, so these are order-ready figures. Find the area closest to yours, or use the calculator for an exact number.
| Area | At 2 inches | At 4 inches |
|---|---|---|
| 50 sq ft | 0.3 yd³ · 0.4 tons | 0.6 yd³ · 0.9 tons |
| 100 sq ft | 0.7 yd³ · 0.9 tons | 1.4 yd³ · 1.9 tons |
| 200 sq ft | 1.4 yd³ · 1.9 tons | 2.7 yd³ · 3.8 tons |
| 500 sq ft | 3.4 yd³ · 4.7 tons | 6.8 yd³ · 9.5 tons |
| 1,000 sq ft | 6.8 yd³ · 9.5 tons | 13.6 yd³ · 19 tons |
How much gravel for common projects?
Different projects use different depths, so the same footprint can need very different amounts of stone. These are typical single-layer figures; a driveway built in layers needs more, which the driveway calculator handles.
- Garden path (3 ft × 40 ft, 2 in): about 0.8 cubic yards — a touch over 1 ton.
- Patio base (12 ft × 12 ft, 3 in): about 1.5 cubic yards — roughly 2.1 tons.
- Fire-pit surround (10 ft circle, 2 in): about 0.5 cubic yards — under 1 ton of pea gravel.
- Single-car driveway top (12 ft × 40 ft, 4 in): about 5.9 cubic yards — 8.3 tons per layer.
What depth of gravel is right?
Depth matters as much as area, and going too deep wastes money. Use this quick reference, and see the sizes and types guide for matching the right stone to each use.
| Project | Depth |
|---|---|
| Decorative bed, path | 2 in |
| Patio or shed base | 3–4 in |
| Driveway top layer | 4 in |
| Drainage / French drain | 4–6 in |
Converting cubic yards to tons and bags
Once you have cubic yards, two quick conversions cover almost every order. For tons, multiply cubic yards by the density — 1.4 for standard gravel. For bags, remember a cubic yard is 27 cubic feet, so it takes about 54 half-cubic-foot (50-lb) bags to equal one cubic yard. Bulk delivery beats bags on price for anything over about half a yard; the cost per ton guide shows the crossover.
How much extra gravel should you order?
Order about 10% more than the bare calculation. Gravel settles and compacts, some is always lost to spillage and raking, and edges are never perfectly square. On sloping or soft ground, bump that to 15%. It is far cheaper to have a wheelbarrow of stone left over than to pay a second delivery fee — and delivery is often the biggest single line on a small gravel order.
Common gravel estimating mistakes
Most short — or wildly over — orders come from the same handful of slips. Avoid these and your estimate will match the truck:
- Forgetting compaction. Loose gravel settles by roughly a quarter, so order for the loose depth you spread, not the thinner finished depth you end up with.
- Mixing units. Measuring width in feet but depth in inches and multiplying them directly is the classic error. Convert depth to feet (inches ÷ 12) first, or let the calculator handle the units.
- Skipping the waste allowance. A dead-exact calculation always comes up a little short once you account for spillage and uneven ground.
- Ignoring slope. A sloped or dished area holds more gravel than its flat footprint suggests — add depth, and lean toward 15% waste.
- Using the wrong density. Converting to tons with a generic weight over- or under-states dense river rock and light pea gravel; pick the right stone type so the tonnage is real.
Every one of these is baked into the calculator’s defaults, which is why the tool is more forgiving than a napkin sketch — but it helps to know why the number lands where it does.