Gravel Calculator

How to use this gravel calculator

What this calculator does. It estimates the rectangular project area, uncompacted geometric volume, order volume after an extra-material allowance, bulk weight, and material cost. It is useful for early purchasing and delivery planning, but it does not determine pavement structure, drainage design, compaction specifications, or whether a particular aggregate is suitable for the site. For engineered roads or heavily loaded driveways, use project specifications and qualified local advice; the Federal Highway Administration gravel roads guide explains broader construction and maintenance considerations.

When to use it. Use the estimate when pricing a garden path, preparing a driveway resurfacing order, sizing a drainage or decorative stone bed, or checking whether a trailer or delivery truck can handle the expected load. Irregular sites can be split into rectangles and calculated separately, then combined.

How to calculate. The calculator opens with a complete demonstration: a 10 m by 2.5 m area, 0.15 m deep, typical gravel density of 1,680 kg/m³, 5% extra material, and a price of $50 per metric tonne. The example workbook is ready immediately. To make your own estimate:

1. Select the Unit system. Metric uses meters, kilograms per cubic meter, cubic meters, and metric tonnes. US customary uses feet, pounds per cubic foot, cubic yards, and short tons. Switching systems converts the current values rather than changing labels only.
2. Choose a Gravel type. The listed options supply planning densities. Choose Custom density when a quarry ticket or supplier specification gives a better value, then enter it in Bulk density.
3. Enter positive numbers for Length, Width, and Compacted depth. Plain decimal notation is accepted; commas and scientific notation are rejected to prevent ambiguous interpretation. Dimensions are required.
4. Set Extra material from 0% to 50%. This optional purchasing allowance covers minor grade variation, spreading loss, and measurement uncertainty. It is not a compaction factor unless your supplier or specification says to use it that way.
5. Choose Price basis and enter Unit price. A mass quote is interpreted as dollars per metric tonne or short ton; a volume quote is dollars per cubic meter or cubic yard. The price may be zero when you only need quantities.
6. Read the live outputs and calculation table. Select Download Excel for a current-state OOXML workbook. Reset clears the demonstration and all entered data; Excel export is then disabled until a complete valid state is entered again.

Input guide. Unit system is required and controls display and quote units. Gravel type is required; its density is an estimate, and changing it affects weight but not volume. Bulk density is required and must be greater than zero; for example, 1,680 kg/m³. Do not confuse loose bulk density with solid rock density. Length and Width are required positive dimensions; the sample values are 10 m and 2.5 m. Compacted depth is also required; 0.15 m means 15 cm, not 0.15 cm. Extra material is optional but must remain between 0 and 50. Price basis is required for cost interpretation, while Unit price accepts a nonnegative dollar amount such as 50. Enter the supplier's quoted basis exactly; mixing a per-ton price with a per-yard selection is a common and costly mistake.

Output guide. Project area is the exact rectangular identity length × width. Base volume is area × depth before extra material. Gravel to order is the primary purchasing estimate and increases with the allowance. Estimated weight multiplies order volume by bulk density; it is a mass estimate and may differ with moisture and gradation. Material cost multiplies either order weight or order volume by the chosen quote. A zero cost means the entered unit price is zero, not that no gravel is needed. The summary pills repeat area, order volume, weight, and cost from the same model. The calculation table shows each formula in both metric and US customary units.

Worked example. The opening area is 10 × 2.5 = 25.00 m². Multiplying by 0.15 m gives 3.75 m³. Adding 5% produces 3.9375 m³, displayed as 3.94 m³. At 1,680 kg/m³, the estimated mass is 6,615 kg, or 6.62 metric tonnes. At $50 per metric tonne, the material cost is $330.75. These values match the first screen and workbook. NIST's guidance on SI volume units explains why area in square meters multiplied by depth in meters yields cubic meters.