Road Base Calculator

1. Enter the area to cover in square feet (length times width).
2. Enter the finished depth you want after compaction, in inches.
3. Pick the base class, or enter a density override from your supplier.
4. Choose a compaction allowance and read the loose tons to order.

Here is what each result line means:

For the same material under its driveway name, see the crusher run calculator.

A road base calculator is a material estimator for the compacted aggregate layer under a road, driveway or slab. It turns the area and the finished compacted depth into a volume in cubic yards and a weight in tons, then adds a compaction allowance so the delivery is enough after rolling.

Road base is dense-graded crushed stone with fines that interlock into a load-bearing layer. DOTs name it by class: Class 2 in California, Class 5 in Minnesota, #21A in Virginia and aggregate base course in the Carolinas. It is the same family as crusher run.

It shares the area-and-depth math of the crushed stone calculator, with the compaction step a base needs.

The divisor 324 folds 12 inches per foot and 27 cubic feet per cubic yard into one step (12 x 27 = 324). The depth you enter is the finished, compacted base depth.

1. Cubic yards = area in square feet times the finished depth in inches, divided by 324.
2. Base tons = cubic yards times the density, about 1.5 tons per cubic yard.
3. Loose tons to order = base tons times one plus the compaction allowance, about 20 percent.

Suppliers sell by the loose ton, so the allowance makes sure the delivery reaches the finished depth after rolling. On a real road the base is tested to a relative-compaction spec.

A 1,000 sq ft road with a 6 in finished base of Class 2 aggregate, density 1.5, with a 20 percent compaction allowance.

Calculation: Volume = 1,000 x 6 / 324 = 18.52 cubic yards. Base tons = 18.52 x 1.5 = 27.78. Loose tons = 27.78 x 1.20 = 33.33 tons to order.

A 500 sq ft driveway at 4 in needs about 11 tons. With the workbook 15 percent factor the road is 27.78 x 1.15 = 31.9 tons.

Finished Depth

Depth sets the volume. A driveway base is about 4 inches, a road 6 to 8, a heavy-truck road more. Place and compact in lifts of no more than 3 to 4 inches.

Compaction Allowance

Loose dense-graded base loses 15 to 25 percent of its volume when rolled, so you order extra. Twenty percent is a safe middle.

Density

Loose road base is about 1.5 tons per cubic yard, with a range of roughly 1.2 to 1.5 by rock and gradation. Use the supplier figure when you have it.

Subgrade Strength

A soft or wet subgrade needs a thicker base or a geotextile, which changes the quantity and is a design decision beyond this estimate.

Moisture

Wet material weighs 10 to 15 percent more, so a weigh-ticket can read heavier than the dry estimate.

DOTs use different names for the same dense-graded aggregate base.

They differ in the exact gradation and local spec, not much in density. The class is a gradation name, not a compaction factor; the required compaction is set by the project spec.

Private Roads and Lanes

Size the aggregate base for a new private road, farm lane or long driveway.

Driveways

Figure the compacted base under a gravel, asphalt or concrete driveway.

Building Pads

Estimate the base under a slab, shop or pole-barn floor.

Parking Areas

Work out the base for a parking pad or equipment yard, then plan a surface with the paver calculator.

Checking a Delivery

Compare a weigh-ticket in tons against the area, finished depth and allowance you used.

1. Ordering the Compacted Volume

Loose base shrinks when rolled. Ordering only the finished volume leaves it thin. Add a compaction allowance.

2. Thick Lifts

A single deep lift will not compact through. Place and roll in 3 to 4 inch lifts.

3. Treating the Allowance as a Spec

The 20 percent allowance is for ordering, not a compaction target. A real road is tested to 95 percent relative compaction.

4. Ignoring the Subgrade

A soft subgrade pumps through a thin base. Fix or stabilize it, or thicken the base.

5. Using a Clean Stone

Open-graded #57 does not bind. A base needs dense-graded aggregate with fines to lock up.

6. Mixing Feet and Inches

Depth is in inches. A 6 inch base is 6, not 0.5.

The calculator estimates the loose tons to order from area, finished depth, density and a compaction allowance.

Multiply the area by the finished depth in inches, divide by 324 for cubic yards, multiply by about 1.5, then add a compaction allowance. A 1,000 sq ft road at 6 in is about 27.8 base tons, roughly 33 tons loose with 20 percent.

About 1.5 tons per cubic yard loose, with a range of roughly 1.2 to 1.5 by rock and gradation. Suppliers sell by the loose ton.

Dense-graded crushed stone with fines that interlock and compact into a load-bearing base under a road, driveway or slab. DOTs call it Class 2, Class 5, #21A or aggregate base course.

Loose dense-graded base loses 15 to 25 percent of its volume when rolled, so order about 20 percent extra to reach the finished depth.

About 4 inches under a driveway and 6 to 8 inches under a road, placed and compacted in lifts of no more than 3 to 4 inches. Heavy-truck roads need more.

Essentially yes. Road base, Class 2, Class 5, ABC and crusher run are dense-graded aggregate bases with regional names and gradations. All compact into a load-bearing layer.

A California DOT dense-graded base aggregate with a required gradation, placed and compacted to at least 95 percent relative compaction. Class 5 and ABC are the equivalents in other states.

At 1.5 tons per cubic yard and 6 inches deep, a ton covers about 36 square feet of finished base. Coverage is 324 divided by the density times the depth.

No. The allowance is a rule of thumb for ordering extra material. A real base is governed by a project or DOT spec, usually 95 percent relative compaction verified by testing.

No. The calculator runs entirely in your browser and nothing is stored or sent.

• Inch Calculator – Gravel Calculator (Cubic-yard math, density and compaction allowance.)
• Caltrans – Class 2 Aggregate Base (Section 26) (DOT aggregate base gradation and 95 percent relative compaction.)
• ASTM D698 / AASHTO T99 – Compaction of Soil and Aggregate (Standard Proctor compaction behind relative-compaction specs.)