A layer ordered by volume and the same material weighed by the supplier can look like different quantities. The connection is bulk density. The Whatson Crush & Gravel Calculator estimates both, using the loose density that you enter.
The density field is editable because this is not a product weighing service. Grading, moisture and the supplied material can make a real delivery different from the example assumption.
The thickness field stays in inches
Choose rectangle or circle. Rectangle uses length and width; circle uses diameter. Those dimensions follow the measurement unit selection.
Layer thickness is different: it is always entered in inches. Even with metres selected for the surface, a four inch layer is entered as 4 in the thickness field.
The calculator multiplies area by thickness and then applies the allowance. Multiplying that ordered volume by the entered kg/m³ density gives the estimated mass.
A 300 sq ft layer
For a rectangle 20 × 15 ft and 4 inches deep, the measured volume is 100 cft. With a 5% allowance, the order becomes 105 cft.
At an assumed loose density of 1,600 kg/m³, the checked result is about 4.757 tonnes. Change the density and that mass changes, even though the volume remains 105 cft.
This example explains why a tonne estimate should not be treated as an exact conversion that applies to all crush deliveries.
Which quote belongs in the rate field?
The rate expects PKR per cft. It prices the ordered volume, including allowance. A quote per tonne cannot be pasted into that field without conversion.
If you obtain a weighed price, use a density appropriate to the quoted material to compare the units. Better still, ask the supplier for the intended volume and weight basis and keep both on the quotation.
Delivery, spreading, compaction and any taxes not included in that rate need separate entries elsewhere.
This is a quantity layer, not a pavement specification
The tool does not choose a suitable aggregate grading, design a base or prove a finished layer is compacted correctly. Enter the depth from the project’s specification rather than choosing it because the calculator has a default.
For circular work, use the full diameter across the area. Entering the radius in a diameter field gives only a quarter of the intended area.
When reviewing the result, check thickness first, density second and quote units third. Those three settings usually explain a large difference between two estimates for the same visible surface.