How to Use the Gravel Calculator
Measure the length and width of the area you are covering and enter them in metres — the header toggle switches the form to feet and inches. Irregular shapes are easiest handled by splitting them into rectangles and adding the volumes; for a curving path, average the width and accept a small error. Measure the surface you want to finish with, and remember that a gravel area normally needs firm edging to hold its shape — gravel on open ground slowly walks sideways.
Depth is the biggest lever in the calculation: at a fixed area, doubling depth doubles the order. For footpaths, 50–75 mm (2–3 in) is the typical range — deep enough to walk on without dispersing, shallow enough not to swallow wheelbarrow wheels. Driveways typically take 100–150 mm (4–6 in) of gravel, compacted in layers onto a compacted sub-base of harder aggregate; spreading 100 mm of gravel straight onto soft ground works it into the mud rather than onto it. Drainage trenches are sized around the pipe plus cover — commonly at least 100 mm of cover over the pipe, though practice varies by application and by region.
Material sets the mass. The four presets carry typical loose bulk densities: crushed stone around 1600 kg/m³, pea gravel around 1700, river rock around 1650 and sand around 1500. Actual figures vary with grading, crushed content and moisture — if your supplier quotes a density for the actual load, enter it in the custom field and the mass follows.
| Material | Typical loose bulk density | Best suited to |
|---|---|---|
| Crushed stone | 1600 kg/m³ | Driveways, paths, sub-base fill — angular particles lock together |
| Pea gravel | 1700 kg/m³ | Decorative beds and paths — rounded, rolls underfoot |
| River rock | 1650 kg/m³ | Decorative features, drainage surrounds — larger rounded stone |
| Sand | 1500 kg/m³ | Bedding layers, jointing, mortar — not a wearing surface |
Loose and compacted volumes are not the same thing. Aggregate delivered loose settles into itself under a plate compactor, so a finished 100 mm compacted layer takes roughly 10–20% more mass than its loose-volume equivalent — compacted bulk density is simply higher than loose. The waste field absorbs this: enter your compacted finished depth and set waste to 20–30%, or enter the loose depth you plan to spread and keep waste near 10%.
Bulk bags versus loose loads is a logistics decision. A typical bulk (dumpy) bag holds about 850 kg — roughly half a cubic metre of crushed stone, covering about 10 m² at 50 mm or 5 m² at 100 mm. A few bags suit small paths and trench fills, all moved by hand. Beyond that, loose aggregate delivered by the tonne is the normal route: one drop, then barrow it out. Either way the tonnes figure is the one to read out, because that is what the supplier actually sells.
What this calculator does not cover: the sub-base underneath, the membrane between ground and gravel, and the edging that holds the finished surface. A driveway sub-base is its own layer of compacted aggregate with its own volume — the gravel sub-base guide covers what goes where, and concrete slab thickness covers slabs that sit on top of prepared fill.