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Gravel & Aggregate Calculator
Ordering gravel, slate, MOT Type 1 or ballast? Punch in your area and depth and get the tonnes and number of bulk bags you need — so you're not left short halfway through a job or paying to send a spare dumpy bag back.
Rule of thumb: 1 tonne of gravel at 50mm covers roughly 12–14 m². Bulk bags vary — this assumes about 0.85 tonnes per bag, so always round up rather than risk running short.
These are estimates. Bulk density varies between products, and loose materials settle and compact — order a little over and confirm the exact figure with your supplier before you buy.
How much gravel do I need?
Multiply the area you're covering (in m²) by the depth (in metres) to get the volume in cubic metres, then multiply that volume by the material's bulk density to get the weight in tonnes. For example, a 20 m² area at 50mm (0.05m) is 1 m³; at a gravel density of 1.6 t/m³ that's about 1.6 tonnes. This tool does the sum for you and rounds the bulk bags up so you don't come up short.
How deep should a gravel driveway or path be?
For a decorative gravel path or border, around 40–50mm of gravel is usually enough to give good coverage without stones migrating everywhere. A gravel driveway needs more — typically a compacted sub-base (such as 100–150mm of MOT Type 1) with a 40–50mm decorative gravel layer on top, so the surface can take vehicle weight without rutting. Calculate the sub-base and the top layer separately, as they use different materials and densities.
How many m² does a tonne of gravel cover?
As a rough guide, one tonne of gravel spread at 50mm deep covers about 12–14 m². Go shallower and it covers more; go deeper and it covers less. Denser materials like MOT Type 1 cover fewer square metres per tonne because more of the weight is packed into the same volume, which is why this calculator asks you to pick the material.
Pouring concrete or landscaping a bed instead?
Pouring a concrete slab, footing or post holes rather than a loose sub-base? Our Concrete Calculator works out the volume and materials for that. Filling a border or raised bed instead of hard standing? See our Topsoil, Compost, Mulch & Bark Calculator for cubic metres and bulk bags of topsoil.
Does this tool store my details?
No. Everything is worked out in your browser as you type — there's no sign-up, nothing is uploaded, and none of your figures are saved or sent anywhere. Refresh the page and it's all gone.
Please note: this tool gives a guide or estimate only. It may not be 100% accurate and is not professional advice — always check the figures before you rely on them. These are ballpark estimates — bulk density varies by product and materials settle, so confirm exact quantities with your supplier before ordering. Everything you type stays in your browser.
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