Calculate tonnage of aggregate for your project
Whether you are creating a gravel driveway, laying a garden path, building a patio sub-base, or covering a border with decorative aggregate, knowing exactly how much material to order prevents both shortages and expensive surplus. Aggregates are heavy and bulky -- getting it wrong means either an incomplete project or tonnes of material you cannot easily return. Different aggregates have different densities, which means the same volume of material weighs different amounts depending on the type. MOT Type 1 (the compactable sub-base material used under driveways and patios) is significantly heavier than decorative slate chips, for example. This calculator accounts for these density differences to give you an accurate weight in tonnes, which is how aggregates are sold by UK builders' merchants and quarries. The depth of aggregate needed varies significantly depending on the application. A decorative gravel path might need only 30-50mm, while a driveway sub-base typically requires 100-150mm of compacted MOT Type 1.
To calculate how much aggregate you need: 1. Enter the length of the area in metres. 2. Enter the width of the area in metres. For irregular shapes, calculate the approximate rectangular area or break the area into sections and calculate each separately. 3. Enter the depth in metres. Common depths: 0.03-0.05m (30-50mm) for decorative gravel on paths, 0.05m (50mm) for border coverage, 0.1-0.15m (100-150mm) for driveway sub-base. 4. Select the aggregate type. Each type has a different density, which affects the total weight: MOT Type 1 is the heaviest (1.8 tonnes/m3), while decorative slate is the lightest (1.4 tonnes/m3). 5. Review the results. The calculator shows the total weight in tonnes, the volume in cubic metres, and the coverage area in square metres. Order in tonnes, as this is how UK suppliers price and deliver aggregates.
The gravel calculation combines simple volume geometry with density conversion: Volume (m3) = length (m) x width (m) x depth (m) Weight (tonnes) = volume (m3) x density (tonnes/m3) The density varies by aggregate type: - Standard gravel (20mm): 1.5 tonnes/m3 - MOT Type 1 (sub-base): 1.8 tonnes/m3 - Pea gravel (10mm): 1.5 tonnes/m3 - Decorative slate: 1.4 tonnes/m3 - Sharp sand: 1.6 tonnes/m3 For example, a 3m x 2m area at 50mm depth with standard gravel: volume = 3 x 2 x 0.05 = 0.3 m3, weight = 0.3 x 1.5 = 0.45 tonnes (450kg). This is roughly half a bulk bag.
Aggregates compact when laid and trafficked, so the finished depth will be less than the loose depth. MOT Type 1 compacts by approximately 25%, so lay it at 25% more than the desired finished depth. Decorative gravels compact less (10-15%). Always lay gravel over a weed membrane to prevent growth through the surface. For driveways, a proper sub-base of MOT Type 1 is essential before laying decorative gravel on top. Most UK suppliers deliver in bulk bags (approximately 850kg each) or loose by tipper lorry for larger quantities.