Gravel Calculator

Gravel is one of the most versatile construction and landscaping materials. It is used for driveways, garden paths, drainage layers under concrete, decorative ground cover, and French drains. Getting the quantity right before ordering saves money on delivery costs and avoids the frustration of running short midway through a project. The calculation involves two steps. First, compute the volume: area multiplied by depth. Second, convert to weight using the bulk density of the gravel type. Different gravel types have different densities because the particle shapes affect how tightly they pack. Crushed angular stone packs more tightly than smooth rounded pebbles. This calculator uses standard bulk density values for three common gravel types. Results include volume in both metric and imperial, weight, and the number of 25 kg bags, which is the most common bag size sold in builders merchants and garden centres.

• Driveway construction: A gravel driveway typically needs 100 to 150 mm depth of compacted crushed stone. Calculate the volume and weight to determine whether to order bulk delivery or bags.
• Garden path installation: Decorative pea gravel paths are typically 50 to 75 mm deep. Calculate the quantity for the path dimensions, then compare bag costs against bulk delivery for the total weight.
• Drainage and hardcore base: A drainage layer under concrete slabs, sheds, or patios typically requires 100 to 150 mm of compacted gravel. Use crushed stone for maximum compaction under load-bearing areas.
• French drain filling: Calculate the volume of a trench (length × width × depth) to find how many tonnes of washed gravel are needed to surround the perforated drain pipe and fill the trench.

• Entering depth in centimetres instead of metres: The depth field is in metres. A 10 cm layer should be entered as 0.1, not 10. Entering 10 gives a volume 100 times too large.
• Forgetting compaction allowance: Gravel compacts by 10 to 20% when tamped. Order 15% extra for driveways and compacted base layers. The calculator gives the theoretical loose volume.
• Using the wrong density for the gravel type: All gravel types look similar but have different bulk densities. Using crushed stone density for river rock (or vice versa) gives a weight estimate that is off by 3 to 10%.
• Ordering bags when bulk is cheaper: For any project over 1 tonne, bulk delivery is almost always cheaper per kg than bags. Check the cost per tonne for a bulk delivery and compare against the bag count multiplied by bag price.

1. 1Enter the length, width, and depth of the area to be covered, all in metres.
2. 2Select the gravel type: pea gravel (1500 kg/m³), crushed stone (1600 kg/m³), or river rock (1650 kg/m³).
3. 3Volume = length × width × depth, in cubic metres.
4. 4Volume in cubic yards = volume × 1.30795.
5. 5Weight in kg = volume × bulk density. Weight in tonnes = weight in kg / 1000.
6. 625 kg bags needed = weight in kg divided by 25, rounded up to the nearest whole bag.

• Order 10 to 15% extra for driveways: Gravel settles and compacts over time, especially in the first few months after installation. Ordering a bit extra means you can top up without buying a new delivery.
• Use a weed membrane under decorative gravel: A weed control fabric under the gravel prevents weed growth from below and stops the gravel from mixing into the soil. It does not add to the gravel calculation but is a worthwhile addition.
• Check vehicle payload before loading bags: Gravel is heavy. A standard car carries roughly 500 kg. Check your vehicle's payload capacity in the owner manual before loading. For large quantities, book a delivery.
• Use crushed angular stone under patios and slabs: Angular crushed stone interlocks when compacted, giving a stable base. Round pea gravel or river rock does not compact as firmly and is not suitable under load-bearing surfaces.