Recycled asphalt millings shrink by 20% when compacted. To end up with a 4-inch deep driveway, you must spread the loose millings 5 inches deep. Use a density of 130 lb/ft³ for the math, not the standard 145.
Asphalt millings—also known as Recycled Asphalt Pavement (RAP)—are one of the best kept secrets in rural driveway construction. When a highway department repaves a road, they use a massive machine to grind off the top few inches of the old road. That ground-up gravel is millings.
They cost 50% to 70% less than fresh hot mix asphalt, they harden over time in the sun, and they don't generate the dust that a standard gravel driveway does. But calculating how much you need requires different math than standard paving.
Fresh hot mix asphalt weighs 145 pounds per cubic foot because it is bound tightly together by hot liquid asphalt cement. Millings are essentially crushed rocks coated in old, dry asphalt. They do not lock together quite as tightly, meaning they weigh less by volume. The industry standard density for calculating RAP is 130 lb/ft³.
This is where homeowners make a massive mistake. When dump trucks drop millings on your driveway, the material is extremely loose and full of air. You will need to rent a heavy vibratory roller to compact it.
Millings compact by about 20%.
If you want a final, hard-packed driveway that is 4 inches thick, you cannot do your math based on 4 inches. You must do your math based on 5 inches of loose material. (4 inches ÷ 0.80 = 5 inches).
Let's look at a 1,000 square foot rural driveway. You want a 4-inch compacted depth.
That is nearly $1,300 in savings just on the raw material, not including the fact that millings are much easier to spread yourself without a professional paving machine.
Our dedicated millings calculator automatically handles the 130 lb/ft³ density and the 20% compaction factor.
Open Millings Calculator