Gravel Calculator — area, depth → tonnes & bags

Real-world use cases

• Order gravel for a new driveway

  You are surfacing a 5 m × 4 m driveway with 50 mm of decorative pea gravel over a compacted sub-base. Set the rectangle to 5 by 4, depth to 50 mm, material to pea gravel (1.6 t/m³), compaction to 0% for the loose top layer. The tool returns 1 m³ → 1.6 tonnes, or 2 bulk bags at 850 kg each. Order 2 bags and you have a small margin for the inevitable spillage and the wheelbarrow you can never empty.

• Estimate a compacted MOT type-1 sub-base

  Under that same driveway you want 150 mm of MOT type-1 crusher run, compacted. Switch the depth to 150 mm, material to crushed stone (1.5 t/m³), and set the compaction allowance to 25% because the plate compactor will eat into the loose volume. For a 20 m² area the tool jumps the loose order from 3 to 3.75 tonnes — the extra 0.75 t is exactly what gets compacted out, and ordering the finished volume would leave you short.

• Fill a French drain or soakaway

  A drainage trench 10 m long, 0.3 m wide, filled 0.4 m deep with clean stone. Use the rectangle at 10 by 0.3, depth 400 mm, material crushed stone. The result tells you the tonnes to order and how many bulk bags — handy because drainage stone is almost always sold loose by the tonne or in dumpy bags, never in neat decorative quantities.

• Top-dress a gravel garden path

  A winding path you measure as roughly 12 m² of coverage, freshening it with 40 mm of new pea gravel. Switch to direct area thinking — measure the path as a rectangle equivalent — set depth 40 mm, and the small-bag count tells you how many 25 kg bags to grab from the garden centre instead of ordering a whole tonne you do not need.

• Price a landscaping job for a client

  You are quoting a client and need the aggregate line item. Enter each area, lay depth and material, read the tonnes, multiply by your supplier's per-tonne rate, and copy the result. The shareable URL reproduces the exact scenario, so you can paste the link into your estimate and the client can see the assumptions — area, depth, material — not just a number you pulled from the air.

Common pitfalls

• Entering depth in the wrong unit. 50 mm is 0.05 m, not 0.5 m. Typing 50 into a "metres" field over-orders by 1000×, and typing 0.5 when you meant 50 mm over-orders by 10×. This tool's depth field is labelled mm (metric) / inches (imperial) precisely so you never confuse it with the metres used for length and width.

• Using radius instead of diameter for a circular area. The circle field asks for the full diameter. Put the radius in and you under-order to a quarter of what you need (area scales with the square of the radius). If you measured across the middle of the circle, that is the diameter — use it directly.

• Ordering the finished compacted volume for a sub-base. Compacted MOT type-1 settles roughly 25% under a plate compactor, so the loose volume you order has to be larger than the hole you are filling. Skipping the compaction allowance is the classic reason a sub-base runs one bag short on the last pass.

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