How GravelMatter calculates

The calculation, step by step

1. Area of each shape, in square feet: rectangle = length × width; circle = π × (diameter ÷ 2)²; triangle = ½ × base × height; or a known area you enter. Areas are summed.
2. Volume = total area × depth (converted to feet). This is the calculated volume.
3. Compaction allowance (if set): calculated volume × compaction %.
4. Waste allowance: (calculated volume + compaction) × waste %.
5. Purchase volume = calculated volume × (1 + compaction) × (1 + waste). The two allowances multiply and are shown on separate lines.
6. Weight = purchase volume (ft³) × density (lb/ft³). US tons = lb ÷ 2,000; tonnes = kg ÷ 1,000.
7. Bulk order = purchase volume and weight rounded up to the next 0.5 yd³ / 0.5 ton (or 0.5 m³ / 0.5 t in metric).
8. Bags = purchase volume ÷ bag volume, or weight ÷ bag weight, rounded up to whole bags.
9. Cost = your unit price × the matching quantity (purchase volume, weight or bag count).

Unit conversions

Internally everything is calculated in feet and pounds, then converted for display. Values are rounded only for display.

Density figures and their sources

Density is the only figure in the calculation that isn't a measurement or a unit definition, and it is the biggest source of error in any volume-to-weight conversion. We use loose bulk density — the weight of a volume of material including the air between the stones.

What the defaults are. For most gravel-type materials we could not find a reliable, publicly available density specific to the product (pea gravel, river rock, crushed stone, decorative rock, road base). Rather than invent separate numbers, these all use the dry-gravel value, 1,680 kg/m³ (105 lb/ft³), from Engineering ToolBox. We show the wider gravel range, 1,460–1,920 kg/m³, from the SME Mining Engineering Handbook as cited in Wikipedia. The note beside each material in the calculators says which is which.

You can override it. Every calculator with a weight output has an editable density. If your supplier publishes a weight per cubic yard, a “tons per yard” factor or a product density, use it. Divide lb per yd³ by 27 to get lb/ft³; multiply tons per yd³ by 74.07 to get lb/ft³.

Why density varies

• Moisture — the reference values for wet and dry gravel differ by about 19%.
• Grading — a mix of sizes, or stone with fines, packs tighter than single-size stone.
• Rock type — the solid rock itself varies in density.
• Shape — rounded and angular stones pack differently.
• Handling — a pile that has just been dumped is looser than one that has settled or been compacted.

Waste allowance

Waste covers spillage, uneven subgrade, edges, and material pressed into soft ground. We don't know of a published standard figure for a home project; the 10% default (5% on the driveway tool, where compaction is added separately) is a planning choice. Change it to suit the site.

Compaction allowance

If you measure the finished, compacted depth, you need more loose material than the geometric volume. The allowance is entered as “extra loose material, as a % of the compacted volume”. The Gravel Roads: Maintenance and Design Manual (SD LTAP for FHWA) notes that ordinary compaction “will result in 30% or greater reduction in volume” in many parts of the country source. A reduction of r needs an allowance of 1 ÷ (1 − r) − 1: 30% reduction → 43% allowance; 20% → 25%; 10% → 11%. The material calculators start at 0% because decorative cover usually isn't compacted. The driveway calculator starts at 20% as a planning allowance — ask your supplier.

Rounding

Bulk material is usually ordered in whole or half units, so the bulk-order line rounds up to the next 0.5 yd³, 0.5 ton, 0.5 m³ or 0.5 t. Your supplier's increments and minimum load may differ. Bags are always rounded up to whole bags. Displayed figures are rounded to 2 decimal places (fewer for large values).

Bags

Bags by volume (ft³ or litres) use the purchase volume. Bags by weight (lb or kg) use the estimated weight, so they depend on the density. Check the bag label: some bags state volume, some weight.

Cost

We don't publish material prices; they vary by region, product and delivery distance. Enter the price from your quote. Cost = unit price × purchase quantity (not the rounded bulk order), so it's an estimate of the material only.

What the calculators don't estimate

• Delivery fees, minimum loads, taxes and equipment hire.
• Excavation, geotextile fabric, edging, culverts or drainage design.
• Slopes: areas are treated as flat plan areas.
• Structural suitability. This site doesn't give engineering advice. For load-bearing, drainage-critical or commercial work, consult a qualified professional.

How the engine is checked

The engine is covered by automated regression tests, including: 10 × 10 ft at 3 in = 25 ft³ = 0.926 yd³; 1 yd³ at 1.4 tons/yd³ = 1.4 tons; 27 ft³ in 0.5 ft³ bags = 54 bags; metric/imperial round trips within 0.1%; and the worked examples on each page. These check the arithmetic, not the real-world density of any material. No material was physically weighed for this site.

Sources

1. Dirt and Mud – Densities. Engineering ToolBox. https://www.engineeringtoolbox.com/dirt-mud-densities-d_1727.html
   Type: Engineering reference table (general values, not product-specific). Used for: Point values: gravel dry 1,680 kg/m³ (105 lb/ft³); gravel wet 2,000 kg/m³ (125 lb/ft³); sand dry 1,555 kg/m³ (97 lb/ft³); sand wet 1,905 kg/m³ (119 lb/ft³).
2. SME Mining Engineering Handbook, 2nd ed. (H. L. Hartman, ed., 1992), as cited in the Wikipedia article “Gravel”. Society for Mining, Metallurgy & Exploration / Wikipedia. https://en.wikipedia.org/wiki/Gravel
   Type: Handbook range via secondary citation. Used for: Range: bulk density of gravel 1,460–1,920 kg/m³ (about 91–120 lb/ft³, 1.23–1.62 US tons per cubic yard). Secondary citation — we have not read the handbook directly.
3. Gravel Roads: Maintenance and Design Manual, Section III – Surface Gravel (K. Skorseth & A. A. Selim, 2000). South Dakota Local Transportation Assistance Program (SD LTAP) for the U.S. Federal Highway Administration; hosted by the U.S. EPA. https://www.epa.gov/sites/default/files/2015-10/documents/2003_07_24_nps_gravelroads_sec3_0.pdf
   Type: Public-agency road manual. Used for: Compaction: ordinary compaction from placement, moisture and traffic “will result in 30% or greater reduction in volume” in many parts of the country (written for gravel roads).
4. Proper Gravel Depth Requirements for Different Driveways. Port Aggregates (aggregate supplier). https://www.portaggregates.com/proper-gravel-depth/
   Type: Supplier guidance (one supplier's recommendation, not a standard). Used for: Driveway depth guidance: light residential 4–6 in total (2–3 in #2 stone base, 2–3 in #57 top); heavy residential 8 in or more; commercial 10–12 in in three layers.
5. ASTM D448 stone size chart (summary of the standard's size numbers). US Made Supply. https://usmadesupply.com/resources/building-codes-standards/astm-ul-general/astm-d448
   Type: Summary of a published standard. Used for: Nominal size ranges for aggregate size numbers such as #2, #4, #57, #67, #8 and #10. The standard itself is ASTM D448; we used this published summary.

Sources were checked 2026-09-26. Found an error? Tell us.