The Formula: How To Calculate Aggregate & Gravel
Calculating the tonnage of aggregate, gravel, tarmac, or sub-base requires converting your dimensions into volume and multiplying by material bulk density:
Weight (Tonnes) = Volume (m³) × Material Density (tonnes/m³) × (1 + Waste Allowance)
A gravel driveway measuring 8m long by 4m wide at a depth of 50mm (0.05m) with 10% waste using decorative gravel (1.6 tonnes/m³):
• Volume = 8 × 4 × 0.05 = 1.60 m³
• With 10% Compaction = 1.60 × 1.10 = 1.76 m³
• Total Weight = 1.76 × 1.6 = 2.82 Metric Tonnes
• Jumbo Bulk Bags = 2,816 kg ÷ 850 kg = 3.31 → Order 4 Bulk Bags
Frequently Asked Questions
What is MOT Type 1 aggregate?
MOT Type 1 (named after Ministry of Transport specifications) is crushed carboniferous limestone, granite, or gritstone crushed to particle sizes ranging from 40mm down to dust. When rolled and compacted, the fine dust locks the larger stones in place to form an ultra-stable load-bearing sub-base for driveways, patios, and highways.
Should I use 10mm or 20mm gravel for a driveway?
Always use 20mm gravel for driveways. 10mm gravel is too small and easily gets stuck in car tyre treads and dragged into your house, while stones larger than 20mm are uncomfortable to walk on.
How much weight does a standard UK bulk bag hold?
Most UK builders' merchants (Travis Perkins, Wickes, B&Q, Jewson) supply jumbo bulk bags containing approximately 800kg to 850kg of material. Always round up to the next full bag to account for uneven sub-ground levels.