Two quotes, two units, no comparison
You ring around for a price on crushed rock. One supplier quotes you per tonne. The next quotes you per cubic metre. You put the two numbers next to each other and pick the lower one.
Except you have not actually compared anything. A price per tonne and a price per cubic metre are two different measurements. Lining the raw numbers up tells you nothing until you convert them to the same unit. Sometimes the mixed units are just how each supplier works. Sometimes they are not an accident. Either way, the fix is the same.
The conversion is just density
Every material has a density, which is how many tonnes fit in a cubic metre. That number is the bridge between the two units. For example, 20mm crushed rock sits around 1.5 to 1.6 tonnes per cubic metre.
A worked example
Supplier A quotes $38 per tonne. Supplier B quotes $58 per cubic metre. At first glance Supplier A looks far cheaper. Now convert, using a density of 1.55 tonnes per cubic metre.
| Supplier | Quoted | Converted | Verdict |
|---|---|---|---|
| Supplier A | $38 / tonne | 38 × 1.55 = ~$59 / m³ | Level |
| Supplier B | $58 / m³ | 58 ÷ 1.55 = ~$37 / tonne | Level |
Same material, same money, once the units match. The $38 was not cheaper. It was the same price wearing a different unit.
Why the per tonne number looks smaller
A per tonne price almost always looks smaller than the per cubic metre price for the same material, because a cubic metre of dense material weighs more than a tonne. That is exactly why a quote in tonnes can feel like a bargain sitting next to a quote in cubic metres, when they are level.
How to protect yourself
Pick one unit and make every supplier quote in it. If they quote in the other unit, convert it yourself before you compare. All you need is the density, and any real supplier will tell you the density of what they are selling. If they will not, that tells you something too.
Buying by weight has a second advantage. Weight can be proven on a weighbridge docket. Volume on a delivery of dense material is an estimate, which is the same problem behind the cubic metre trap. At NXT Quarry we price and bill dense material by weight, off dockets you can see, so there is nothing to convert and nothing hidden. See how NXT Control shows every tonne on your account, live.