Calculation methodology

The core principle: volume first

Every calculator starts from geometry: the area you measure multiplied by the finished depth you choose. That volume depends only on your measurements, so it is marked Calculated and is always available.

Weight is a second, optional step. It needs the bulk density of the actual product, which we do not assume. When you supply one, the weight is marked Estimated.

Geometry

• Rectangle: area = length × width. A square is a rectangle with equal sides.
• Circle: area = π × radius². A diameter is halved to give the radius.
• Triangle: area = base × perpendicular height ÷ 2.
• Known area: the area you enter.
• Multiple sections: each section's volume is calculated, then added.

There is no irregular-shape drawing tool. For an irregular area, measure it and enter it as a known area, or split it into simple shapes.

Volume = Area × Finished depth

With feet and inches: cubic yards = length (ft) × width (ft) × depth (in) ÷ 324.

Unit conversion

All conversion factors come from the NIST Guide to the SI (Special Publication 811), Appendix B.8. Calculations run internally in SI units and are converted for display.

• 1 in = 0.0254 m; 1 ft = 0.3048 m; 1 yd = 0.9144 m (international definitions, not the US survey foot)
• 1 yd³ = 27 ft³ = 0.7645549 m³
• 1 US short ton = 2,000 lb = 907.1847 kg; 1 metric tonne = 1,000 kg

Mass is always labelled as US short tons or metric tonnes — never an unqualified “ton”. Long tons and litres are not used.

When you switch between US and metric units, values you have already entered are converted, not reinterpreted.

Bulk density and weight

Weight = Volume × Bulk density

Bulk density is the mass of a quantity of aggregate divided by the whole volume it occupies, including the spaces between particles. It differs between loose and compacted material. Particle density (specific gravity) describes the solid rock alone and is never used to turn a volume of gravel into weight.

No generic material densities

Our source review found no defensible nationwide bulk density for pea gravel, river rock, crushed stone, crusher run, limestone, #57 stone, decomposed granite or road base. Product names do not fix the rock, grading, fines, moisture or condition. Choosing a material on this site never supplies a density.

Weight therefore comes from a density you enter from your supplier, with its condition recorded. A future verified product density would be offered only for a named product with its supplier, location, grading, condition, measurement basis and source dates; none qualify at launch.

Conditions must match

A loose delivered density applies to a loose volume; a compacted density to a compacted volume. If the condition is unknown the calculation proceeds with a warning.

Extra material / handling allowance

Order volume = Required volume × (1 + allowance)

The allowance starts at 0%. It is your choice, for waste, handling or contingency. It is separate from compaction and is never labelled as a recommendation.

Compaction and yield

Compaction controls appear only on the Gravel Driveway, Crusher Run, Road Base and Paver Base calculators. You can enter one of two figures from your supplier or project:

Loose volume = Compacted volume ÷ (1 − volume reduction)

Loose volume = Compacted volume ÷ loose-to-compacted yield

A volume reduction must be less than 100%. The allowance is applied after this step. There is no automatic compaction factor: engineering targets such as “95% of maximum dry density” are density-test requirements, not an instruction to add 5% more material.

Project calculators

• Gravel driveway: sections are added into one project area; one shared layer stack is applied to it. Each layer is calculated separately, with its own optional density, compaction and allowance. Totals are grouped by material.
• Paver base: base and optional bedding layers. CMHA's ideal-condition minimum depths can fill the base depth only when you select them; editing the value marks it as user supplied. No adjustment for poor conditions is applied.
• French drain: trench envelope minus full pipe displacement (length × π × outside diameter² ÷ 4), only when the whole pipe sits within the gravel. Partial overlaps are not estimated.
• Aquarium: tank floor area minus flat excluded footprints, through the full substrate depth. Weight and bags need the product's own density or packaging data: bag volume, bag weight plus product density, or the manufacturer's coverage at its stated depth.
• Riprap: treated surface area × your designed thickness, plus any toe or key volume you enter. No hydraulic sizing, and no conversion from plan dimensions and slope.
• Cost: quantity in the pricing unit × price, plus delivery fee, distance surcharge and sales tax (applied to material cost). Density is requested only when converting between volume and weight pricing. Bags come from the bag volume, the bag weight plus product density, or the manufacturer's coverage for the product — applied only at the manufacturer's stated depth, never scaled or inferred — and are rounded up.

Result labels

• Calculated: geometry and exact unit conversions.
• Calculated from your inputs / your allowance: volumes adjusted with compaction or allowance figures you entered.
• Estimated: anything that depends on a density, a price or packaging data — weight, tons-to-yards conversions, cost and bag counts.
• Needs more information: a result that cannot be given without data you have not supplied, such as weight without a density.
• Educational reference: a sourced value you chose to use, such as a CMHA paver-base depth.

Every result lists the assumptions used and where each number came from: User supplied, Verified external source or Calculated.

Rounding

Calculations keep full precision internally. Cubic yards and cubic metres are shown to two decimal places, cubic feet to one, US short tons and metric tonnes to two, and very small values to three significant figures. Step-by-step breakdowns show intermediate values to four decimal places.

Source review

Every external source is recorded with its organization, document, link, the date the source was published or revised (where the source states one), and the date we reviewed it. These dates are kept separate: Source reviewed, and Source published or Source revised. Only NIST conversion factors enter calculations automatically. The full list is on the Sources page.