Download the checklist
Keep the practical checks, caution notes, and next steps handy while comparing options.
Download checklist From measured area to an order quantity
The calculator exposes the three assumptions that most often change an order: finished layer depth, aggregate density, and the allowance for uneven ground, compaction, and handling loss.
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Measure one layer
Multiply length by width by depth to calculate volume. Treat structural sub-base and decorative gravel as separate layers rather than adding their depths together.
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Convert volume to weight
Multiply cubic metres by the selected tonnes-per-cubic-metre density. Product density can vary, so supplier data should replace the preset when available.
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Apply the project allowance
Add the percentage you choose for site variation and losses, then divide by bag size. Bag counts round up; larger projects should also be compared with bulk delivery.
How this estimate works
The calculator turns the finished surface area and gravel depth into cubic metres, then converts that volume into weight using the density you choose. It includes a 10% allowance for settling, small measuring errors, and losses around edges, then rounds bag counts up because suppliers sell whole bags.
- Volume = length x width x depth, with depth converted to metres.
- Weight = volume x selected aggregate density.
- The entered waste and settling allowance is applied before bag count is rounded up.
- US cubic yards and tons are shown as exact unit conversions of the metric estimate.
Before ordering gravel
Check the depth for the intended use, measure the actual finished area after edging, and compare small bags with bulk-bag or loose-load delivery. For driveways, shed bases, and other load-bearing jobs, confirm the sub-base and drainage build-up before treating the decorative gravel quantity as the whole job.
Gravel coverage examples
These examples use a 10% allowance and 1.6 t/m3 density. They are useful for sense-checking, but supplier density, bag weight, moisture, compaction, and the finished build-up can change the actual order.
| Area and depth | Approximate volume | Approximate weight |
| 3 x 1 m at 4 cm | 0.12 m3 | 0.21 tonnes |
| 5 x 2 m at 5 cm | 0.5 m3 | 0.88 tonnes |
| 8 x 1 m at 5 cm | 0.4 m3 | 0.7 tonnes |
| 10 x 3 m at 5 cm | 1.5 m3 | 2.64 tonnes |
| 4 x 4 m at 7.5 cm | 1.2 m3 | 2.11 tonnes |
| 20 m2 at 5 cm | 1.0 m3 | 1.76 tonnes |
FAQ
What depth should gravel be?
It depends on the project. Decorative borders can often be estimated with a shallower finished depth than paths, while driveways and bases need separate checks for sub-base, drainage, and compaction. Use the calculator to compare depths, then confirm the build-up for load-bearing work.
Should I add extra?
Yes, a small allowance is sensible for settlement, measuring errors, edging losses, and small spills. The calculator uses a 10% allowance. For awkward shapes, uneven ground, or long edges, check whether a larger allowance is prudent before ordering.
Does this work in cubic yards and US tons?
Yes. The result shows volume in cubic metres and cubic yards, and weight in tonnes and US tons, so you can order in either metric or US-customary units.
How do I use the calculator for bulk bags?
Enter the supplier's bulk bag weight in the bag size field. For example, use 850 if the bag is listed as 850 kg. The calculator divides the estimated kg by that bag weight and rounds up to the next whole bag.
Why does aggregate density change the result?
The area and depth give volume, but many suppliers sell by weight. Density converts cubic metres into tonnes or kg. Pea gravel, slate chippings, cobbles, and sub-base materials can have different densities, so supplier data should replace the default when available.
Can I use this for MOT Type 1 or sub-base material?
You can use it as a quantity estimator by choosing the MOT Type 1 preset or entering a custom density, but calculate sub-base layers separately from decorative gravel. This calculator does not decide the correct structural build-up for a driveway, patio, or base.
How should I measure an irregular gravel area?
Split the area into rectangles where possible, calculate each area, and add them together. For curves, use an average width and add a sensible allowance. Exclude fixed features such as steps, drains, planters, and paving that will not be covered.
Why do supplier coverage estimates differ?
Coverage estimates depend on depth, aggregate density, bag weight, moisture, and how full a bulk bag is. A supplier quote at 3 cm depth is not comparable with your project if you plan to lay 5 cm or 7.5 cm.
Should I order small bags or bulk bags?
Small bags are convenient for small borders and touch-up jobs. Bulk bags or loose delivery usually make more sense for larger areas, but check delivery access, drop-off location, handling effort, and the exact bag weight before comparing prices.
Can I rely on this for a driveway?
Use it to estimate the visible gravel or selected aggregate layer, not as driveway construction advice. Driveways may need a compacted sub-base, edge restraints, drainage, and a project-specific depth.