Road Base / Sub-Base Calculator
Enter the area dimensions and depth to calculate the volume, tonnage, and truckloads of road base or sub-base aggregate material needed, with compaction and waste factors.
Estimate only — not professional advice. Always verify results independently before purchasing materials or beginning work. Terms of Use
What is Road Base / Sub-Base?
A road base calculator estimates the quantity of crushed aggregate material needed to construct the base or sub-base layer of a road, driveway, parking area, or building pad. The base course is the compacted layer of granular material placed between the subgrade soil and the surface course (asphalt or concrete). It distributes vehicle loads, provides drainage, and prevents the surface from cracking and settling. Accurate quantity estimation is critical because aggregate is sold by weight (tons) and delivered by the truckload. The calculation starts with the loose volume of material needed to fill the area: length times width times depth, converted from cubic feet to cubic yards. But here is the key factor that catches many estimators off guard: crushed aggregate compacts significantly when rolled or tamped into place. A typical compaction factor for crushed limestone or recycled concrete base is 20 percent, meaning loose material loses 20 percent of its volume when compacted to specification. To achieve the desired compacted depth, you must order more loose material than the finished volume. A 20 percent compaction factor means you need 1.2 times the finished volume. Weight conversion uses the density of the specific aggregate. Crushed limestone and recycled concrete aggregate typically weigh about 1.5 tons per cubic yard (approximately 2,700 pounds per cubic yard) in a loose state. This density varies by material: clean gravel runs about 1.4 tons per yard, dense-graded aggregate (DGA or crusher run) runs about 1.5 tons, and recycled concrete can range from 1.3 to 1.6 tons depending on composition. Delivery trucks are rated by weight capacity. A standard tandem-axle dump truck carries approximately 20 tons of aggregate per load, though this varies by truck size and local weight restrictions. Tri-axle trucks may carry 25 tons and transfer trucks up to 30 tons. The calculator rounds up to whole truckloads since you cannot order a fractional load. A waste factor of 5 percent accounts for material lost during spreading, grading, and edge spillage. For rough terrain or sites with poor access, increase the waste factor to 8 to 10 percent. Under-ordering road base means an additional delivery charge and potential delays, so it is better to have a small surplus than to run short.
How to Calculate
- Measure the length of the area to be based in feet
- Measure the width of the area in feet
- Determine the required compacted depth in inches (6 inches is standard for driveways, 8-12 inches for roads)
- Set the compaction factor (20% is typical for crushed aggregate)
- Set the waste factor (5% for flat, accessible sites)
- Review the volume, tonnage, and truckload count
- Confirm the aggregate type and density with your supplier before ordering
Formula
Volume (cu ft) = Length x Width x (Depth / 12) Volume (cu yd) = Volume (cu ft) / 27 Volume After Compaction = Volume (cu yd) x (1 + Compaction Factor / 100) Volume With Waste = Volume After Compaction x (1 + Waste Factor / 100) Tons = Volume With Waste x 1.5 (density of crushed aggregate) Truckloads = ceiling(Tons / 20) The compaction factor increases the order quantity because loose material compresses to a smaller volume. The density of 1.5 tons per cubic yard is standard for crushed limestone and recycled concrete base. The "Volume to Order" output shown by the calculator is the Volume With Waste figure — that is, the compacted volume already increased by the 5% waste factor. This is the number to place on your supplier order.
Example Calculation
A 100 ft x 12 ft driveway base, 6 inches deep, 20% compaction, 5% waste: Volume = 100 x 12 x (6/12) = 600 cu ft Volume = 600 / 27 = 22.22 cu yd After Compaction = 22.22 x 1.20 = 26.67 cu yd With Waste = 26.67 x 1.05 = 28.0 cu yd Tons = 28.0 x 1.5 = 42.0 tons Truckloads = ceil(42.0 / 20) = 3 truckloads
Frequently Asked Questions
What is the difference between road base and sub-base?
Sub-base is the lower layer placed directly on the subgrade soil, typically 6 to 12 inches of coarser material like crusher run or recycled concrete. Road base (or base course) sits on top of the sub-base and directly below the surface course, using finer, more tightly graded aggregate. Not all projects need both layers — residential driveways often use a single 6-inch base course over compacted soil.
How thick should my road base be?
For residential driveways, 4 to 6 inches of compacted base is typical. Light commercial parking areas need 6 to 8 inches. Public roads and heavy-traffic areas require 8 to 12 inches or more, often split between a sub-base and base course. The required thickness depends on soil conditions, expected traffic loads, and local engineering standards.
What aggregate types are used for road base?
Common materials include crusher run (a blend of crushed stone and stone dust), dense-graded aggregate (DGA), recycled concrete aggregate (RCA), and gravel. Crusher run and DGA are preferred because the mix of sizes locks together and compacts to a dense, stable surface. Clean gravel without fines does not compact as well and is better suited for drainage applications.
Why do I need to account for compaction?
Loose aggregate has air voids between the particles. When compacted with a roller or plate compactor, these voids close and the material settles to a smaller volume. Crushed stone typically compacts 15 to 25 percent depending on the gradation and moisture content. If you order only the finished volume, you will end up with a base layer that is significantly thinner than designed.
How do I compact road base properly?
Spread the material in lifts (layers) of no more than 4 inches of loose depth. Moisten each lift to near optimum moisture content — the material should hold together when squeezed but not drip water. Compact each lift with a vibratory plate compactor (for small areas) or a vibratory roller (for large areas) until no further settlement is visible, typically 3 to 5 passes. Test compaction with a nuclear density gauge or proof roll for critical applications.