Asphalt Calculator

How the asphalt calculator works

Asphalt (hot mix, often called bitumen in Australia) is ordered by the tonne. The calculator works out the volume of the layer and multiplies it by the compacted density:

Asphalt (kg) = length (m) × width (m) × compacted depth (m) × density (kg/m³)

Divide by 1,000 for tonnes. Enter every dimension in metres, so a 50 mm layer is 0.05.

Worked example: a 12 m × 3.5 m driveway, 50 mm thick

1. Area: 12 × 3.5 = 42 m²
2. Depth 50 mm = 0.05 m, so volume = 42 × 0.05 = 2.1 m³
3. Compacted density of dense-graded asphalt: about 2,350 kg/m³
4. 2.1 × 2,350 = 4,935 kg, or about 4.9 tonnes, so order about 5.2 tonnes with a small allowance for edges and levels

Typical thicknesses

The asphalt is a wearing surface. Its strength comes from a well-compacted base underneath, typically 100–200 mm of crushed rock for driveways. On clay, a weak base leads to cracking and potholes, whatever the asphalt thickness.

Density

Compacted dense-graded asphalt usually sits between 2,300 and 2,450 kg/m³. Loose asphalt in the truck is lighter by volume, which is why you should order by tonne using compacted depth.

Common mistakes

• Entering thickness in millimetres.
• Forgetting the base course, which usually costs more than the asphalt.
• Designing no fall. Driveways need drainage, typically at least a 1–2% cross-fall away from buildings.

How many tonnes of asphalt per square metre?

At 50 mm compacted, about 0.118 tonnes (118 kg) per m². At 30 mm, about 70 kg per m².

Is asphalt cheaper than concrete for a driveway?

Often cheaper to lay, but it needs resealing over time. Concrete costs more upfront and usually needs less maintenance.

How long before I can drive on new asphalt?

Usually within a day for cars, but avoid sharp steering turns and heavy vehicles for a few days, especially in hot weather.

Written by Sam Alex, civil engineer. About the author