Convert m³ to tonnes get instant, accurate results with bulk bag ∓ tipper load estimates.
Ask a builders' merchant for "a cubic metre of gravel" and they'll tell you what it weighs without blinking. Ask them the same question about topsoil, or sand, or bark mulch, and the number changes every time — even though the space it takes up on your driveway is identical. That's the whole puzzle behind converting cubic metres to tonnes: volume and weight are related, but never in the same way twice, because the material sitting inside that cubic metre is doing all the work.
The calculator above handles that conversion both ways — m³ to tonnes, and tonnes back to m³ — across 72 materials, from dry sand to structural steel. This article walks through why the two units aren't interchangeable, exactly how to get the most out of every part of the calculator, and gives you a reference table and FAQ section for the numbers people search for most: how many tonnes are in a cubic metre of sand, gravel, topsoil, concrete, and a few others besides.
Why a Cubic Metre and a Tonne Aren't the Same Thing
A cubic metre is a measure of space — a box one metre along each edge. A tonne is a measure of mass. There's no fixed bridge between the two unless you know what's filling that box. Pack it with fresh water and you're carrying almost exactly one tonne. Pack the same box with dry building sand and you're closer to 1.6 tonnes. Fill it with bark mulch instead and you'd struggle to hit 0.35 of a tonne, because most of that "cubic metre" is actually air trapped between loose chippings of bark.
The property that connects the two is density — how much mass is packed into each unit of volume, usually written as kilograms per cubic metre (kg/m³) or tonnes per cubic metre (t/m³). Once you know a material's density, the sum is simple multiplication:
This is exactly why a generic "cubic metres to tonnes converter" that doesn't ask what material you're moving can only ever be a guess. It's also why the calculator above starts by asking you to pick a material (or set your own density) before it converts anything — get that one number right and everything downstream, from the tonnage to the number of bulk bags, follows correctly.
In practice, this trips people up in a specific way: builders' merchants and quarries almost always sell aggregate by weight (tonnes), because that's what goes on the weighbridge ticket. But you plan a job — a patio base, a driveway sub-base, a raised bed — by volume (m³), because that's what actually fills the space. Somewhere in between, someone has to convert one into the other, and that's the gap this tool is built to close.
How to Use This Cubic Metres to Tonnes Calculator
The calculator works in three modes, switched using the tabs at the top: Volume, Dimensions, and Tonnes to m³ (the reverse direction). Whichever one you use, the material and density you set apply across all three, so you only need to set that up once per session.
1. Volume mode — you already know your m³
Tap the Material card and search or browse to the one you're working with — sand, MOT Type 1, topsoil, concrete and 68 others are built in, grouped by category (aggregates, soil, construction, stone, metals, liquids, timber, agriculture and more).
Type your volume into the Volume field, or use one of the quick-select amounts (1, 2, 5, 10 m³ and so on) to save typing. You're not locked into cubic metres either — the small unit tag next to the field switches between m³, ft³, yd³, litres, UK gallons and US gallons.
If you want to add a safety margin for compaction, spillage or overfill, tap a waste allowance percentage (or type your own). This inflates the volume before it's converted, so the tonnage you're shown already includes the buffer.
Your result appears instantly: the headline tonnage, plus the same figure in kilograms, UK long tons, US short tons and pounds, and a practical guide underneath translating that into bulk bags, lorry loads or IBC tanks depending on what you've picked.
2. Dimensions mode — you haven't worked out the volume yet
If all you've got is a tape measure, switch to Dimensions instead of doing the m³ sum in your head first. Choose Box for a rectangular area (a patio, a trench, a raised bed) and enter length, width and depth — each with its own independent unit, so you can measure length and width in metres but depth in millimetres, which is how most tradespeople naturally think about a sub-base or bedding layer. Choose Round for a circular footing or post hole and enter diameter and depth instead; the calculator applies the correct cylinder formula (πr² × depth) rather than treating it as a box. Either way, the running volume is shown live above the fields as you type, before it's carried through to a tonnage below.
3. Tonnes to m³ mode — you've got a delivery weight and need the space
This is the reverse problem: a supplier has quoted you, say, 20 tonnes of MOT Type 1, and you need to know how much ground that will actually cover, or how many trips it'll take. Enter the weight (with the same unit flexibility — tonnes, kilograms, UK or US tons, pounds) and the calculator divides by the density instead of multiplying, giving you the volume in m³ along with cubic feet, cubic yards, litres and UK gallons.
Setting a custom density
Not every material fits neatly into a preset list. If your supplier has given you a specific figure — a delivery ticket, a data sheet, a lab test — open the material picker and choose Custom density at the top. You can type the figure in either kg/m³ or t/m³ using the small unit switch beside the Density field, and the calculator will flag it clearly if you've edited a preset material's density away from its default value.
Advanced options: bulk bags, tipper loads and IBC tanks
Underneath the main inputs, Advanced options expands three extra fields that feed the practical guide shown with your result, rather than the headline number itself:
- Bulk bag (kg) — this one is genuinely automatic. As soon as you pick a material (or type a density), the calculator estimates a realistic bulk bag weight for it, based on a standard bag holding roughly 0.8 m³. Pick something dense like wet sand and the suggested bag weight rises; pick something light like bark and it falls. If your supplier quotes a different figure, just type over it — the moment you edit it manually, the "Auto" badge disappears and your figure sticks until you reset.
- Tipper (t) — defaults to 20 tonnes, a fair approximation of a standard UK tipper lorry's rated payload, but it's yours to change if your hire company or site vehicle carries more or less.
- IBC tank (L) — defaults to 1,000 litres, the standard IBC container size used across the UK for bulk liquids, again fully editable.
These three don't all apply at once — the calculator only surfaces the ones relevant to your chosen material. Pick sand, gravel, topsoil or a construction material and you'll see bag and tipper figures; pick a liquid such as water, diesel or vegetable oil and the IBC figure takes over instead; pick something like steel, timber or grain and neither applies, so the guide simply tells you how many times heavier than water your material is.
Typical Densities for UK Building and Garden Materials
These are the same nominal density figures used inside the calculator above, pulled out here as a quick reference. All are loose bulk densities unless stated otherwise — real deliveries vary with moisture, particle size and compaction, so treat these as planning figures and confirm the exact number with your supplier before ordering.
| Material | kg/m³ | t/m³ | Category |
|---|---|---|---|
| Bark mulch | 350 | 0.35 | Soil & garden |
| Topsoil – loose | 1,200 | 1.20 | Soil & garden |
| Topsoil – settled | 1,500 | 1.50 | Soil & garden |
| Sand – dry | 1,600 | 1.60 | Aggregates |
| Sand – wet | 1,920 | 1.92 | Aggregates |
| Gravel – loose, dry | 1,520 | 1.52 | Aggregates |
| Gravel – wet | 2,000 | 2.00 | Aggregates |
| Ballast (all–in) | 1,700 | 1.70 | Aggregates |
| MOT Type 1 – loose | 1,600 | 1.60 | Aggregates |
| MOT Type 1 – compacted | 2,100 | 2.10 | Aggregates |
| Cement – loose (Portland) | 1,440 | 1.44 | Construction |
| Concrete – plain | 2,300 | 2.30 | Construction |
| Concrete – reinforced | 2,400 | 2.40 | Construction |
| Asphalt / tarmac | 2,300 | 2.30 | Construction |
| Granite | 2,700 | 2.70 | Natural stone |
| Water – fresh | 1,000 | 1.00 | Liquids |
| Diesel | 850 | 0.85 | Liquids |
| Steel | 7,850 | 7.85 | Metals |
Need a material that isn't on this shortlist? The calculator above covers 72 in total, including timber, agricultural produce and half a dozen more metals — open the material picker and search rather than scrolling.
How Density Compares Across Common Materials
Six common materials on the same scale — note that a cubic metre of granite weighs almost eight times as much as the same volume of bark mulch. Metals like steel run far higher still (around 7,850 kg/m³) and aren't shown here so the lighter materials stay readable.
Working Out Bulk Bags, Tipper Loads and IBC Tanks
Knowing the tonnage is only half the job on site — the next question is usually "how many bags is that" or "how many trips will this take". That's what the practical guide underneath your result is built for, and it's worth understanding how each figure is reached.
Worked example — aggregate delivery. Say you need 5 m³ of gravel at 1.7 t/m³. That's 5 × 1.7 = 8.5 tonnes. A standard bulk bag holding around 1,360 kg of gravel (0.8 m³ × 1,700 kg/m³, the auto-suggested figure) would need 8,500 ÷ 1,360 = 6.25, rounded up to 7 bulk bags. On a 20-tonne tipper, that same 8.5 tonnes fits comfortably in a single load.
Bulk bags (also called jumbo bags, tonne bags or dumpy bags, depending on the merchant) are sold as roughly one cubic metre containers, but they're rarely filled to a full cubic metre of heavy aggregate — doing so would make them too heavy to lift safely with standard equipment. Most suppliers fill them to somewhere around 0.7–0.85 m³, which is why the weight per bag shifts with the material rather than staying fixed: a bag of dense wet sand and a bag of light bark mulch hold roughly the same volume but very different weights.
Worked example — liquid delivery. 3,000 litres of diesel needs to go into standard 1,000 L IBC totes. That's 3,000 ÷ 1,000 = exactly 3 tanks. Order 3,200 litres instead and you'd round up to 4 tanks, since suppliers don't split a delivery across a part-filled container.
Tipper capacity is simpler in one sense — it's a fixed rating for the vehicle rather than something that changes with material — but it catches people out because weight limits, not volume, are usually what stop a tipper being loaded further. A 20-tonne tipper reaches its weight limit at around 8.3 m³ of concrete, but doesn't reach it until roughly 12.5 m³ of dry sand, purely because sand is lighter per cubic metre. If you're planning multiple loads, always work from the tonnage rather than assuming a fixed volume per lorry.
Frequently Asked Questions
How many tonnes are in a cubic metre of sand?
Dry building or sharp sand is typically around 1.6 tonnes per cubic metre. Wet sand holds more water between the grains and rises to roughly 1.9–2.0 tonnes per cubic metre for the same volume, so it's worth checking with your supplier whether their figure is for dry or as-delivered wet sand before you order.
How many tonnes are in a cubic metre of gravel?
Loose, dry gravel comes in at around 1.5 tonnes per cubic metre, rising to about 2.0 tonnes per cubic metre when wet. Compacted sub-base gravels such as MOT Type 1 are denser again once laid and rolled — typically 2.0–2.1 tonnes per cubic metre — because compaction squeezes out the air gaps between particles.
How many tonnes are in a cubic metre of topsoil?
Freshly dug, loose topsoil is around 1.2 tonnes per cubic metre. Once it's had time to settle and compact naturally it moves closer to 1.5 tonnes per cubic metre. Topsoil with a lot of organic matter or added compost tends to sit lower still, since organic material is lighter than mineral soil for the same volume.
How much does a cubic metre of concrete weigh?
Reinforced concrete works out at roughly 2.4 tonnes per cubic metre, and plain (unreinforced) concrete is a touch lighter at around 2.3 tonnes per cubic metre. This is the figure UK ready-mix suppliers use as standard, though it can shift slightly depending on the exact mix design and aggregate used.
How many tonnes fit in a standard bulk bag?
It depends entirely on what's in the bag, because bulk bags are filled to a set volume (around 0.7–0.85 m³) rather than a set weight. For dense aggregate like sand or gravel, that usually works out to somewhere between 0.8 and 1 tonne. For much lighter material like bark or wood chip, the same size bag might only weigh a quarter of that.
Should I order aggregate by volume (m³) or by weight (tonnes)?
Most UK builders' merchants and quarries price and deliver aggregate by weight, since that's what a weighbridge measures. But you'll usually plan the job itself — how much space needs filling — in volume. Work out your volume first, convert it to tonnes using the material's density, and order that weight, adding a small waste allowance to cover compaction and spillage.
Why does the same volume weigh differently depending on the material?
Weight depends on how tightly packed the particles are and how much of that "solid" material is actually there versus empty space between grains. A cubic metre of steel has almost no gaps in it, so nearly the whole volume is dense metal. A cubic metre of bark mulch is mostly air pockets between loose chippings, so most of that space contains nothing at all — hence the huge difference in weight for an identical volume.
Can I use this calculator for wet or compacted material?
Yes — many materials in the list have separate wet and dry (or loose and compacted) entries, precisely because moisture and compaction change the density enough to matter. If your material sits between two listed densities, or your supplier has given you an exact figure, switch to Custom density and enter that number directly rather than relying on a generic preset.
How many cubic metres are in a tonne of aggregate?
Again, it depends on the density, but as a rough planning figure, a tonne of average aggregate (sand, gravel or ballast around 1.6–1.7 t/m³) works out to roughly 0.6 cubic metres. Switch the calculator above to Tonnes to m³ mode, enter your weight and pick the exact material for a precise figure rather than this rough average.
Is a "tonne bag" always exactly one tonne?
Not usually. "Tonne bag" is a common trade name for a standard bulk bag, but most are filled to somewhere between 800 kg and a tonne of aggregate for safe handling, rarely a full 1,000 kg. Always check the actual filled weight with your supplier rather than assuming the name is literal.
All figures on this page and in the calculator above are nominal averages for planning purposes. Real-world density varies with moisture content, particle size, source and compaction, so always confirm the exact figure with your supplier before placing an order or relying on a calculation for anything safety- or cost-critical.
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