Net gravel volume in cubic yards = area (sq ft) × added depth (in) / 324. A 20 × 12-foot rectangle at a selected 4-inch layer depth contains 80 cu ft, or 2.962963 cu yd. The formula measures space; it does not choose the right gravel, design the base or establish how many loose delivered yards produce a compacted layer. Use the gravel calculator after choosing those inputs.
Measure the actual layer
- Use length × width only for a rectangle. Measuring the longest and widest dimensions of an irregular area gives its bounding rectangle, not its true area.
- Split irregular areas into non-overlapping sections and subtract spaces that will not receive gravel. Add unrounded volumes.
- Use the actual added depth for a top-up, not automatically the full existing base depth.
- For several material layers, calculate each layer’s area and thickness separately. An excavation depth is not always the gravel depth.
- For variable-depth ground, use smaller measured sections or a site survey rather than one guessed average.
Formula and unit conversions
Cu ft = net area (sq ft) × added depth (in) / 12.
Cu yd = net area × added depth (in) / 324.
US short tons = matching cu yd × matching lb per cu yd / 2,000.
One cubic yard is 27 cubic feet. Keep full precision through conversions; round only display values and the final supplier sales quantity.
Net cubic yards by area and selected layer depth
| Net area | 2 in | 3 in | 4 in | 6 in | 8 in |
|---|---|---|---|---|---|
| 100 sq ft | 0.617 | 0.926 | 1.235 | 1.852 | 2.469 |
| 200 sq ft | 1.235 | 1.852 | 2.469 | 3.704 | 4.938 |
| 500 sq ft | 3.086 | 4.630 | 6.173 | 9.259 | 12.346 |
| 1,000 sq ft | 6.173 | 9.259 | 12.346 | 18.519 | 24.691 |
The chart shows geometric volume at the selected layer depth, rounded for display. It includes no density, conversion, reserve or sales increment. Depths are calculation examples, not recommended designs for every walkway, driveway, slab or drain.
Loose volume versus compacted volume
FHWA’s earthwork guidance distinguishes material in its original ground position, loose material during transport and compacted fill. It says the measurement basis must be specified and project-specific material characteristics matter.1 If the target is a compacted layer, ask for a defined loose-to-finished conversion for that material and condition. A generic “add 10%” does not establish it.
If a confirmed relationship is 1.15 loose yards per finished yard, multiply finished volume by 1.15. If instead a confirmed statement says loose volume reduces by 15%, divide finished volume by 0.85. These statements are different. They are arithmetic definitions, not recommended gravel factors. Keep any separate handling reserve distinct and do not double-count losses already included in the conversion.
Choose material and depth for the actual project
| Project | What must be resolved before quantity |
|---|---|
| Walkway or decorative bed | Surface material, selected depth, edging and any separate base |
| Driveway or parking area | Subgrade, traffic/loading, drainage and separate base/surface layers |
| Pavers or slab support | Project-specified base material and finished compacted thickness |
| Shed support | Foundation requirements, footprint and required base construction |
| Drainage trench | Designed cross section, pipe/displacement and suitable drainage material |
This quantity guide does not give one universal gravel depth or material for all those uses. For drainage, excavation and fill are not the same volume when a pipe or other component occupies space. For structural work or significant grade changes, confirm the design and required material/testing rather than treating this chart as approval.
Three checked examples
1. A rectangular loose layer with a selected reserve
A 20 × 12-foot area at a selected 4-inch loose added layer: 20 × 12 × 4 / 12 = 80 cu ft = 2.962963 loose cu yd. A hypothetical chosen 10% handling reserve gives 88 cu ft = 3.259259 loose cu yd. At a matching hypothetical supplier value of 1.4 US short tons/loose yd, net mass is 4.148148 short tons; with the selected reserve it is 4.562963 short tons. The reserve is not a verified compaction rate.
2. An L-shaped top-up area
Split a non-overlapping L into a 20 × 6-foot rectangle and a 8 × 4-foot rectangle: 120 + 32 = 152 sq ft. At a selected uniform 2-inch added depth, volume = 152 × 2 / 12 = 25.333333 cu ft = 0.938272 cu yd. With stated 0.5-cu-ft bags, round up 25.333333… / 0.5 = 51 bags. This count uses actual labeled volume, not bag weight. It includes no allowance or material-specific conversion.
3. Two separately specified finished layers
For a selected 30 × 10-foot horizontal footprint, a hypothetical 4-inch finished base is 100 cu ft = 3.703704 finished cu yd. A separate 2-inch finished surface is 50 cu ft = 1.851852 finished cu yd. Suppose project-specific relationships are hypothetically 1.20 loose/finished for the base and 1.10 for the surface: loose targets are 4.444444 and 2.037037 cu yd, respectively. If each product is sold in quarter-yard increments, round each separately to 4.5 and 2.25 loose cu yd. These thicknesses and factors illustrate the math; they do not prescribe a construction design.
Weight and supplier order units
American Rock Supply lists approximate calculator reference values of 1.50 US short tons/yd for crusher run/road base, 1.40 for several gravel/crushed-stone products and 1.35 for river rock.2 Its table does not define separate moisture and loose/compacted bases for every value. Use the exact product’s matching supplier density, not a universal range or a reference value as a maximum delivery weight.
Follow the supplier’s actual billing unit and increment. There is no blanket advantage to ordering by tons instead of yards. Ask whether volume is loose or another measured state, and which ton unit is used. Available vehicle payload and axle/trailer limits matter as well as cubic capacity; a quantity estimate is not hauling permission.
FAQ
How much does one cubic yard cover?
Geometrically: 324 sq ft at 1 inch, 162 at 2 inches, 108 at 3 inches, 81 at 4 inches or 54 at 6 inches. If a delivered loose yard must become a compacted layer, use the verified conversion before treating that as finished coverage.
How much extra should I order?
Resolve a defined material conversion first, then any distinct handling reserve and supplier increment. No universal allowance is verified by this guide.
Can I convert a 50-lb bag to cubic feet?
Not from weight alone. Use the actual labeled volume/yield, or a verified matching density.
Does this estimate give the delivered cost?
No. Compare current quotes for the required product and rounded order, including minimums, delivery, fees, tax and unused surplus.
Related tools and guides
Gravel calculator | Convert yards and US short tons | Driveway quantities | Walkway quantities | Gravel coverage per yard | Measure irregular areas
Sources
- Federal Highway Administration: Earthwork Design (volume states and project-specific estimating information)
- American Rock Supply: Gravel calculator and guide (approximate supplier reference pound/yard and ton/yard values)