Asphalt is ordered by the ton, laid in two courses and quoted by the square yard, and those three units are why estimating it goes wrong. This asphalt calculator takes the area and the thickness of each course, then returns the tonnage of the base course, the tonnage of the surface course and the total, because those are two deliveries at two prices rather than one number.
Why it asks for two thicknesses
A driveway is not one slab of asphalt. The Colorado Asphalt Pavement Association puts the ordinary residential build at a 2 inch bottom course with a 1.5 inch surface course over it, and the two are different mixes: the base is coarser and cheaper, the surface finer and dearer. A calculator that asks for a single depth hides the split that the invoice is going to show you anyway.
Both figures here are compacted thickness, which is what a specification states and what an inspector measures. Loose mix out of the truck sits higher than what you end up with, and closing that gap is the paving crew with the roller, not something your order has to allow for.
Tons out, volume underneath
Volume is how the arithmetic works and weight is how the material is sold, so the page shows both. The bridge between them is the unit weight of compacted hot mix, about 145 pounds per cubic foot.
Tonnage of one course
tons = area × thickness ÷ 12 × density ÷ 2,000
Run once for the base course, once for the surface, then add the allowance
The trade often states the same density per square yard instead. The Indiana DOT design manual publishes 110 pounds per square yard per inch of compacted mixture in its roadway quantities factors, which works out to 146.7 pounds per cubic foot, so 145 is a round number sitting in the same place. If your supplier quotes a unit weight for their mix, use theirs: density is an input here rather than a constant, because it is printed on paperwork you already have.
Five percent, not ten
Most material calculators default to a ten percent allowance and this one does not. Hot mix cannot be returned, cannot be stored and arrives at around 300 degrees with the clock running, so an overage is money burned rather than material put aside for later. Five percent covers the thin spots and what the wheelbarrow keeps. Anything beyond that is a surcharge you are charging yourself.
Why the square yard figure is there
Paving is quoted per square yard, so a contractor price comes back in units the tape measure never gave you. The page prints the area in square yards beside the tonnage so a quote can be checked in the units it was written in. A 40 by 12 foot driveway is 480 square feet, which is 53.3 square yards.
Asphalt calculator FAQ
A 40 by 12 foot driveway built the usual way, a 2 inch base course under a 1.5 inch surface course, takes about 10.7 tons at 145 pounds per cubic foot with a 5 percent allowance. Change either thickness and the tonnage moves with it.
At 145 pounds per cubic foot a ton is 13.8 cubic feet, which spread 2 inches thick covers about 83 square feet, or a little over 9 square yards. The published highway factor of 110 pounds per square yard per inch says the same thing a shade more conservatively.
Plants sell it by the ton and paving contractors quote by the square yard, which is why this page prints both. Multiply the square yards by the thickness factor to check a quote against a plant price.
