Granite Cubic Metre to Square Metre: How Much Area Does One Cubic Metre Cover?
One cubic metre of granite covers 1 ÷ thickness in metres square metres: 50 m² at 20mm, 33.3 m² at 30mm, 20 m² at 50mm. That is geometry alone, before saw kerf and offcuts — and it is exactly the gap between the cubic metres a supplier invoices and the square metres you receive.
How many square metres does one cubic metre of granite give?
Thickness alone decides it: square metres = 1 ÷ thickness in metres. Spread one cubic metre into 20mm slabs and it covers 1 ÷ 0.02 = 50 m²; at 30mm it is 33.3 m²; at 50mm it is 20 m². Double the thickness and the area halves, no exceptions. The table is pure geometry and assumes the whole cubic metre turns into sound slabs of even thickness. Real output is always lower, and that shortfall is the yield rate dealt with in the next section. One distinction matters: the cubic metre here is solid finished stone, not the rough block with missing corners sitting in the yard. Sesame White G603, which we cut regularly, follows this table at 30mm.
| Thickness | m² from 1 m³ | m³ per m² |
|---|---|---|
| 20mm | 50 m² | 0.020 m³ |
| 25mm | 40 m² | 0.025 m³ |
| 30mm | 33.3 m² | 0.030 m³ |
| 40mm | 25 m² | 0.040 m³ |
| 50mm | 20 m² | 0.050 m³ |
Why do the supplier's cubic metres and square metres never match?
Because the two ends are traded in different units: blocks and slabs by volume, finished panels by area, with three losses in between. Saw kerf comes first — every cut removes a few millimetres, and more cuts remove more. Offcuts come second: a size that does not fit the slab layout leaves narrow strips nobody can reuse. Defects come third: colour lines, rust spots and hairline cracks are cut out. Together they make the yield rate.
What yield rate should I use, and why can't I copy a number?
There is no universal figure, only the one your own order measures. Do not copy someone else's percentage, and do not accept a spoken 'usually about seventy percent': the same quarry shifts its yield from one bench to the next and from one order size to another, so last order's figure does not carry over to this one. Cut one batch of your own order and divide finished square metres by cubic metres fed in; that is a number you can defend. Then write into the quotation whether pricing runs per finished square metre or per cubic metre fed in — that clause settles more arguments than any percentage.
Working backwards: how much block does 100 m² of 30mm need?
Two steps: finished volume, then divide by yield. Finished volume = area × thickness. 100 m² of 30mm is 100 × 0.03 = 3 m³. At a yield of 0.7 you need 3 ÷ 0.7 ≈ 4.3 m³ of block. In one line: block volume = finished area × thickness in metres ÷ yield. The 0.7 is an assumed figure used to show the arithmetic, not a measured value from our yard, so replace it with your own. The reverse works too: 6 m³ of block at 0.7 yield gives 6 × 0.7 ÷ 0.03 = 140 m² of 30mm. Compare that with the cubic metres on the supplier's invoice, and if the gap is wide, ask which yield he used.
What does a cubic metre weigh, and why does that set the freight basis?
About 2.7 tonnes. At a density of 2.7 t/m³ one cubic metre weighs 2.7 tonnes; a 30mm slab weighs 81 kg per m², which is the same statement twice (81 ÷ 0.03 = 2700). LCL shipments and many freight clauses charge on W/M, whichever is greater between weight tons and volume tons. Granite at 2.7 tonnes per cubic metre is always charged on weight, so your freight basis differs from a shipper of light cargo. Full containers follow the same logic: 346 m² of 30mm in a 20ft container is about 10.4 m³ and about 28 tonnes, so the payload limit arrives before the space runs out. The weight table by thickness is not repeated here; how much loading margin to leave is covered in the loading note linked at the end.
One quote is per cubic metre and the other per square metre — how do I compare?
Convert both to a price per square metre: square-metre price = cubic-metre price × thickness in metres. One cubic metre yields 1 ÷ thickness square metres, so one square metre occupies exactly its thickness in cubic metres. Multiply a 30mm cubic price by 0.03 and a 50mm price by 0.05. Then check three things, or the numbers will compare while the basis does not: first, whether the price is per finished net area or per cubic metre fed in; second, who carries the loss, included in the unit price or billed separately; third, whether the thickness quoted is rough or finished, since a 30mm rough panel may leave the polisher at 28mm and the area basis shifts by a few percent. Without those three, the converted figure is only an indication.
What should I ask the supplier before placing the order?
Five questions. Put the answers into the proforma invoice or a contract annex before you discuss unit price.
| Question | Why it matters |
|---|---|
| Is this batch priced per cubic metre or per square metre? | It sets the base for every number that follows |
| What yield did you use, and how do I verify it? | It is the bridge between cubic and square metres |
| Is the thickness quoted rough or finished? | Polishing removes thickness, so the area basis moves |
| What kerf width did you allow for in the layout? | The number of cuts sets the first loss |
| Can you send the slab layout drawing? | With the drawing you can check the square metres yourself |