How to use the volume calculator
- Choose Imperial or Metric.
- For each area, choose a shape, enter its dimensions and the depth. Depth is entered in inches or millimetres for convenience.
- Add rows for separate beds, trenches or holes. Use the count for identical ones, such as several post holes.
- Enter a swell or shrink factor if needed.
- Optionally enter the supplier’s density to estimate the weight.
How the volume is calculated
Each row’s plan area is calculated with the shape formulas (rectangle, triangle, circle or trapezoid), multiplied by its depth and its count. The rows are added and the factor is applied: volume × (1 + factor ÷ 100). Results are shown in cubic metres, cubic yards and cubic feet. If you enter a density, weight = volume (m³) × density (kg/m³) ÷ 1,000 tonnes.
Worked examples
Raised bed. 16 × 12 ft, 1 ft deep: 192 ft³ = 7.11 yd³ = 5.44 m³.
Gravel driveway. 5 m × 4 m at 300 mm deep: 6 m³ (7.85 yd³). If the supplier says their gravel weighs a particular number of kilograms per cubic metre, enter it to see the tonnage to order.
Post holes. Ten round holes 250 mm across and 750 mm deep: π × 0.125² × 0.75 × 10 = 0.37 m³.
How to interpret the results
Suppliers sell bulk material by the cubic yard, the cubic metre or the tonne. Round up to their minimum increment. If they sell by weight, the density you enter has the biggest effect on the result, so use the supplier’s own figure.
Tips and common mistakes
- Depth units: 4 in is 0.333 ft, not 0.4 ft. The calculator handles this for you when you enter depth in inches.
- Account for compaction: gravel bases are usually compacted, so order more than the finished volume.
- Measure in several places on uneven ground and use an average depth.
- Allow for access: bulk deliveries are dumped in one spot; plan for moving the material.
Assumptions and limitations
The calculator treats each section as a prism with a flat top and bottom. For irregular excavations, split the area into simpler shapes or use an average depth.