How asphalt quantity is calculated
A road asphalt calculator finds the area you're paving, multiplies it by the compacted layer thickness to get volume, and multiplies that volume by the asphalt mix's density to get the weight you'll order. Asphalt plants sell hot mix by weight, in tonnes, so the weight is the figure to give your supplier.
The formulas
- Area = Road length × Road width
- Volume = Area × Thickness
- Weight (kg) = Volume × Density
- Weight (tonnes) = Weight (kg) ÷ 1,000
Length and width default to meters and thickness to millimeters. Each accepts mm, cm, m, ft or in. Density is entered in kg/m³, defaulting to 2,400, and the calculator accepts values from 1,000 to 3,000. Area is rounded to two decimals, volume and tonnes to three, and kilograms to one.
Worked examples
Two-lane road surface: 100 m long, 7 m wide, a 50 mm wearing course, default density.
- Area: 100 × 7 = 700.00 m².
- Volume: 700 × 0.05 = 35.000 m³.
- Weight: 35 × 2,400 = 84,000.0 kg, or 84.000 tonnes.
Driveway: 20 m long, 3 m wide, 60 mm thick, with a mix the supplier quotes at 2,300 kg/m³.
- Area: 20 × 3 = 60.00 m².
- Volume: 60 × 0.06 = 3.600 m³.
- Weight: 3.6 × 2,300 = 8,280.0 kg, or 8.280 tonnes.
At the default 2,400 kg/m³ the driveway would come to 8.64 tonnes. On a small job a density difference of 100 kg/m³ is only a few hundred kilograms, but on a long road it can be several truckloads.
Tonnes per 100 m² by layer thickness
Because weight scales directly with thickness, a quick reference helps when comparing options. These use the 2,400 kg/m³ default:
| Compacted thickness | Volume per 100 m² | Weight per 100 m² |
|---|---|---|
| 25 mm | 2.5 m³ | 6.0 t |
| 40 mm | 4.0 m³ | 9.6 t |
| 50 mm | 5.0 m³ | 12.0 t |
| 75 mm | 7.5 m³ | 18.0 t |
| 100 mm | 10.0 m³ | 24.0 t |
For a different density, multiply the weight by your density ÷ 2,400.
Choosing the density
The density of compacted asphalt depends on its aggregate, binder content and how well it's compacted, so it varies between mixes and suppliers. The handler's default assumes a dense, well-compacted hot mix at the top of the typical 2,200 to 2,400 kg/m³ range. If your supplier quotes a bulk specific gravity for the compacted mix, multiply it by about 1,000 to get kg/m³. Open-graded and porous mixes contain more air and are lighter.
Steps to estimate a paving job
- Measure the length and width of each rectangular area. Split curves and tapers into rectangles or triangles and add the areas.
- Enter the compacted thickness of the layer you're ordering. If the job has a base course and a wearing course, calculate each layer separately.
- Enter the density for that specific mix.
- Add an allowance for edges, low spots in the base and material left in the equipment, then round up to the supplier's minimum order or truck size.
Limitations
- Assumes a uniform thickness over a flat rectangle. Camber, crossfall and patching to fill low spots add material.
- Doesn't estimate tack coat, base aggregate or sub-base.
- The tonnes shown are metric tonnes. US quantities in short tons need the conversion in the FAQ, based on the exact pound defined in NIST SP 811.
Pavement layer thicknesses for public roads, and for driveways carrying heavy vehicles, should come from your local highway authority's specification or a qualified pavement engineer.
Related calculators
- Excavation calculator: volume to dig out for the road base.
- Concrete calculator: for a concrete driveway or kerb instead of asphalt.
- Construction materials converter: convert asphalt between weight and volume.
- Weight converter: convert kilograms and tonnes to pounds.
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