Methodology
What this site calculates, what it assumes, and where those assumptions stop being reliable.
Exact conversions and assumed ones
It is worth separating the two, because they fail in different ways. The conversions are exact: 12 inches to a foot, 3 feet to a yard, 27 cubic feet to a cubic yard, 2000 pounds to a short ton, and 0.3048 metres to a foot by international definition. Those are arithmetic and cannot be wrong. The density is not exact. It is an assumption, and it is the one number in the whole calculation that carries real uncertainty.
Where the densities come from
The figures used here are the typical loose, dry bulk densities that aggregate suppliers publish for each material, and each one is shown with the range it is commonly quoted within. They are planning assumptions, not measurements, not a standard, and not certified by anyone. This site does not test materials and does not claim to. The most accurate calculation available to you is the one that uses the density your own supplier quotes for the pile you are buying, which is why that field is editable everywhere it appears.
Allowances and compaction
The waste allowance is applied once, at the end, to volume and weight together, so the two can never drift apart. It is never applied silently: the result panel shows what the job needs, what the allowance adds, and what to order as three separate figures. Compaction is treated the same way, as an adjustable allowance rather than a hidden multiplier, because how much a material settles depends on the material and the equipment, and a single universal factor would be a made up number dressed as a fact.
Rounding, and the one rule about it
Three different numbers are in play and this site keeps them apart. The exact value carries through the whole pipeline unrounded. The display value is the same number shown to a readable number of decimal places. The order value is rounded up to something a supplier will actually sell, and it is the only one allowed to change what you buy. The rule that follows: no value that changes a purchase is ever rounded silently, and the exact figure stays visible next to it.
The reverse calculations
The coverage and depth pages run the same engine backwards, with one deliberate difference: no allowance is added. An allowance exists to make an order big enough. Applying it to material you already own would overstate how far that material goes, which is the opposite of useful, so those pages report what the pile will actually do.
Layered builds, trenches and truckloads
A driveway or a paver base is not one depth of one material. Each layer runs through the same core calculation on its own, with its own material and its own depth, and the layers are added together afterward, so a three layer driveway gives exactly the answer three separate single layer calculations would. A French drain trench is not solid gravel either: the perforated pipe running through it displaces volume, modelled as a cylinder at the pipe's outer diameter and subtracted from the trench before the gravel figure is worked out, which is what stops a long run of trench overstating what it needs. Truckloads are counted in whole loads, always rounded up, because no supplier delivers two thirds of a load; the final partial load and the capacity you are paying for but not using are both shown as their own figures rather than folded into one number.
What this site does not do
It does not know your local prices, your soil, your drainage or your building code. It is not engineering advice and nothing on it is a substitute for a specification. The depths offered as presets are common starting points, not requirements. For anything structural, anything carrying vehicle loads, or anything your local building department has rules about, use what they require and treat the number here as a shopping estimate.
Frequently asked questions
Why does my supplier quote a different tonnage?
Almost always because their density differs from the typical value used here. Bulk density genuinely varies with the parent rock, the grading, the moisture content and how much the material has settled in the stockpile, and a yard weighing its own product will know its own figure better than any published average. Enter theirs in the density field and the results match. If the difference is large and the density is not the reason, check that you are both talking about the same depth.
How accurate is this calculator?
The arithmetic is exact. The answer is as accurate as the two inputs that carry uncertainty: your measurements and the density. A careful measurement and a supplier density will land close. A rough pace of the area and a generic density will not, and no calculator can fix that. This is also why the allowance exists, and why the working is shown rather than hidden.
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