Construction & trade New Zealand
Gravel Calculator New Zealand
Gravel and metal are sold by the cubic metre or the tonne, and the two are not the same because a cubic metre weighs well over a tonne. Enter the area and the depth to see both, with a little extra for settling and waste, and the number of loads for your trailer.
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A typical figure you can change. Ask your supplier for theirs.
Gives a rough cost.
Order about
—Volume before waste
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Weight
—
Loads of your trailer
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Rough cost
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Surface area covered
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The working
How much gravel do I need?
Multiply the area by the depth, add an allowance for waste and settling, and round up. A 10 m by 3 m area at 75 mm deep is 2.25 m³, and with 10% extra you should order 2.5 m³, which weighs about 4.0 tonnes. Loose gravel weighs roughly 1.5 to 1.8 tonnes per cubic metre depending on the type and moisture.
Choosing the depth
A decorative garden path may need only 25 to 50 mm of gravel, a driveway usually wants 100 mm or more of compacted aggregate, and a base under pavers or concrete is often 75 to 100 mm. Gravel compacts, so order about 15 to 20% extra to end up at the finished depth. Edging and a geotextile layer help keep the stones in place and stop weeds.
Types of aggregate
Washed river stones and decorative chips are used for looks, while crushed metal or basecourse compacts and drains well and makes a solid driveway or path base. Sizes range from fine to 40 mm or more. Ask the supplier which suits your job, because a fine-grained product behaves very differently from coarse rock.
To cover a larger area, measure it first with the cubic meter calculator.
How this is calculated
The rule, step by step, so you can check any figure by hand.
area = length × width, or π × (diameter ÷ 2)² for a round areavolume = area × depth (in metres)volume to order = volume × (1 + waste ÷ 100), rounded up to 0.1 m³weight = volume to order × tonnes per cubic metreloads = volume to order ÷ the size of your trailer or truck, rounded up
Always measure the area and the depth carefully, and add the allowance for waste and settling. Loose gravel weighs roughly 1.5 to 1.8 tonnes per cubic metre depending on the type and moisture. Weights are typical values: moisture, compaction and the source of the material all change them, so use your supplier's figure when you have it.
The volume is rounded up to the next tenth of a cubic metre because suppliers sell in whole or half loads. A small job may be cheaper by the bag or by the trailer load than as a delivered bulk order, so ask for prices both ways.
A worked example
A 10 m by 3 m area, 75 mm deep, 10% waste.
- Area30 m²
- Volume2.25 m³
- With 10% waste2.475 m³
- To order2.5 m³
- Weight4.0 tonnes
Order about 2.5 m³.
Ask your supplier whether they sell by volume or by weight.
Delivery and handling
A cubic metre of gravel can fill a small trailer, but its weight is more than many trailers are rated to carry, so check the load limit. Bulk deliveries are tipped in one place and need moving by barrow, so plan access.
What it leaves out
Uneven ground, compaction and the exact density of your material are not modelled. The weight uses a typical figure, and prices vary by region and supplier.
What this calculator does not do
- Level, even depth assumed
- Typical weights you can change
- Rounded up to 0.1 m³
- An estimate for ordering
Common questions
How much gravel do I need?
Multiply area by depth, add waste and round up.
How do I convert cubic metres to tonnes?
Multiply by the weight per cubic metre; the tool uses a typical figure you can change.
How much extra should I order?
About 10%, more for uneven ground or settling.
Can I use a trailer?
Yes, but check its load limit, because gravel is heavy.
Is the cost exact?
No. It is the volume times the price you enter.
Where these numbers come from
- Wolfram MathWorld — cuboid Volume of a box: length × width × height. Fixed formula, nothing to go out of date
- Building Performance — MBIE Guidance on ground preparation and building work in New Zealand
Method last reviewed 2026-10-28 This calculator uses fixed rules rather than rates that change, and its method is re-checked against the sources above at least once a year. Out of date? Tell us and we will fix it.
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