What you need
A tape measure long enough for the longest side (a 25 ft / 8 m tape covers most garden jobs; a long reel tape helps for driveways), stakes or spray paint to mark the edge, and something to write on. Measure in one unit throughout — feet or metres — and set the same unit in the calculator.
Rectangles and L-shapes
Measure length and width at right angles. If opposite sides differ, use the average of the two. An L-shape is two rectangles: measure each one so they don't overlap, and add them as separate areas.
At 3 in deep that is 2.30 yd³, or 2.53 yd³ with 10% waste — a 3.0 yd³ bulk order (≈ 3.58 tons at 105 lb/ft³). Open this in the gravel calculator →
Circles and tree rings
Measure the diameter — straight across through the centre. The calculator uses area = π × (diameter ÷ 2)². The calculators add areas together; they can't subtract one. For a ring around a trunk or planter, work out the ring yourself (outer circle minus inner circle) and enter it as a Known area — or accept the small overestimate as part of your waste margin.
Corners and triangles
An angled corner is a triangle: measure the base and the height at right angles to it. The calculator uses ½ × base × height.
Curved beds and paths
For a curved strip, measure the length along the centre line and take the width at several evenly spaced points. Average the widths and treat it as a rectangle.
| Widths measured | 3.5 ft, 4 ft, 4.5 ft, 3 ft |
|---|---|
| Average width | 3.75 ft |
| Area | 24 × 3.75 = 90 ft² |
| At 3 in + 10% waste | 0.92 yd³ → order 1.0 yd³ |
For irregular blobs, sketch the shape on paper and break it into rectangles and triangles; small errors at the edges are what the waste allowance is for.
Measuring depth
Depth is the thickness of the finished layer. For new work, decide it in advance (see depth and coverage). For an existing excavation or a top-up, push a ruler down at several points and average them: readings of 2.5, 3, 3.5, 2 in average 2.75 in. Enter the average, not the deepest point.
If the depth you want is the compacted depth — for a base that will be plate-compacted or driven on — note it. The calculators handle that with a separate compaction allowance rather than by changing the depth.
Units
Length and width can be in feet, inches, yards, metres or centimetres; depth in inches, feet, centimetres or metres. Check the depth unit especially: entering 3 with the depth unit on feet instead of inches gives 12× the volume (11.11 yd³ instead of 0.93 yd³ for a 10 × 10 ft area). The calculators warn above 24 in.
Slopes
The calculators treat every area as flat. On a gentle slope, measuring along the ground surface rather than horizontally gives a slightly larger area, which errs on the side of enough material. On steep ground, gravel tends to migrate downhill — that's a design question, not a quantity one.
Measuring checklist
- Mark the edges before measuring.
- Split the area into rectangles, circles and triangles.
- Measure each shape in the same unit.
- Take several depth readings and average them.
- Note whether the depth is loose or compacted.
- Enter each shape as its own area in the calculator.