How this calculator works
This page converts an area and a depth into a gravel order. It measures the area, applies the finished depth to get a volume, then adds two separate allowances before telling you what to buy.
The two allowances do different jobs and are easy to confuse. Compaction accounts for the fact that loose stone settles: if you want four inches of compacted base, tipping four inches of loose stone will not get you there. Waste covers the ordinary losses of spreading a bulk material around, including spillage off the barrow, edges that need over-filling and material that disappears into soft ground.
Tonnage is the primary answer because that is usually how aggregate is sold. It is shown as a range, and that is not hedging: bulk density genuinely moves with moisture content, gradation and rock type, so the same cubic yard of stone can weigh noticeably different amounts on different days from different pits.
The formula
Five steps, of which only the last two involve any assumptions at all.
- Area
length (ft) × width (ft) - Convert the depth to feet
depth in inches ÷ 12 - Finished volume in cubic yards
area (ft²) × depth (ft) ÷ 27 - Add compaction, then waste
volume × (1 + compaction ÷ 100) × (1 + waste ÷ 100) - Convert to weight
loose volume × bulk density
Cubic yards per 100 square feet, by depth
Geometry only: no density, no compaction and no waste. This is the number to check a quote against before any allowances are added.
| Finished depth | Cubic feet per 100 ft² | Cubic yards per 100 ft² |
|---|---|---|
| 1 in | 8.33 | 0.31 |
| 2 in | 16.67 | 0.62 |
| 3 in | 25.00 | 0.93 |
| 4 in | 33.33 | 1.23 |
| 6 in | 50.00 | 1.85 |
Add your compaction and waste allowances on top of these figures. A compacted base typically needs meaningfully more loose material than this table alone suggests.
Frequently asked questions
Should I order by the ton or by the yard?
Order in whatever unit your supplier sells in, and use the other figure as a cross-check. Yards are a volume and tons are a weight, so converting between them requires a density. That is exactly the number that varies. If the two figures from your supplier and this page disagree substantially, the density assumption is usually why. Ask them for theirs.
Why does compaction increase the amount rather than reduce it?
Because you are specifying the depth you want at the end, not the depth you start with. Compacting drives the air out of loose stone and the surface drops, so reaching a four-inch compacted base means placing more than four inches of loose material. If you are spreading decorative gravel and not compacting it at all, set the compaction allowance to zero.
Does the type of gravel change how much I need?
It changes the weight, not the volume. A cubic yard is a cubic yard whatever is in it, but angular crushed stone and rounded pea gravel pack differently and weigh differently, so the tonnage moves even when the volume does not. That is why the material selector affects the tons and the cost but leaves the cubic yards alone.
What if my area is not a neat rectangle?
Split it into pieces you can measure, work each one out, and add the volumes. Awkward curves are usually close enough to a rectangle plus a triangle, or a rectangle minus a corner. Rounding up slightly on an irregular shape is the right instinct because the waste allowance exists partly for this.
Variables and units
For the default “Rectangular area” mode. Other modes label their own fields in the calculator.
material- Material: unitless.
length- Length: ft, in, yd, cm, m.
width- Width: ft, in, yd, cm, m.
depth- Depth: in, ft, yd, cm, m.
compaction- Compaction allowance: %; optional.
waste- Waste allowance: %; optional.
density- Your supplier’s density: lb/ft³; optional.
price- Price per ton: per ton; optional.
Worked example: a 30 ft by 10 ft driveway strip
You are topping up a driveway 30 ft long and 10 ft wide with crushed stone to a finished, compacted depth of 4 in. Because it will be compacted, the loose quantity you order has to be larger than the finished geometry suggests.
| Field | Value |
|---|---|
| Material | Crushed stone / angular gravel |
| Length | 30 ft |
| Width | 10 ft |
| Depth | 4 in |
| Compaction allowance | 20 % |
| Waste allowance | 10 % |
| Price per ton | 0 per ton |
| Result | Value |
|---|---|
| Order this much | 6.27–6.93 US tons |
| Loose volume to order | 4.89 yd³ |
| Area being covered | 300 ft² |
These figures are generated by the same calculation the calculator above uses, so they update automatically if the method changes.
Where these numbers come from
Draft: not yet published or indexed
| Assumption | Value used | Status |
|---|---|---|
| Bulk density of common crushed stone and gravel.Bulk density shifts with moisture, gradation and rock type. Suppliers publish figures for their own material, so ask for it before ordering by weight. Applicability: Launch-market starting value only. A future market must supply reviewed regional or product-specific provenance before overriding it. You can replace this with your own figure. | 95–105 lb/ft³ | Not yet verified |
| Bulk density of rounded pea gravel.Rounded gravels pack differently from angular crushed stone. Confirm with your supplier. Applicability: Launch-market starting value only. A future market must supply reviewed regional or product-specific provenance before overriding it. You can replace this with your own figure. | 95–105 lb/ft³ | Not yet verified |
| Default compaction allowance for a compacted aggregate base.Loose aggregate loses volume when compacted, so a compacted finished depth needs more loose material than its geometry suggests. The real figure depends on the material and the compaction effort. Applicability: Launch-market starting value only. A future market must supply reviewed regional or product-specific provenance before overriding it. You can replace this with your own figure. | 20% | Not yet verified |
| Default aggregate waste allowance.Covers spillage during delivery and spreading, and edges that need over-filling. Applicability: Launch-market starting value only. A future market must supply reviewed regional or product-specific provenance before overriding it. You can replace this with your own figure. | 10% | Not yet verified |
This figure is a working placeholder. It has not yet been checked against the source listed, so treat it as indicative and confirm with your supplier.
Sources
- ASTM C29/C29M, Standard Test Method for Bulk Density ("Unit Weight") and Voids in Aggregate: ASTM International Not yet checked
- Gravel Roads Construction and Maintenance Guide: US Federal Highway Administration Not yet checked
Published by Material Totals. Review the calculation methodology and source registry.
Suggested citation: Material Totals, “Gravel Calculator,” https://materialtotals.com/gravel-calculator/
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