Road Base Calculator
Enter your road or driveway dimensions, choose a material, set a compaction allowance, and get the volume in cubic yards or cubic metres, the weight in tons, and an optional cost estimate - all with step-by-step working. Switch between metric and imperial units at any time.
What is road base material?
Road base (also called road base aggregate, base course, or crushed base) is a layer of compacted granular material placed beneath asphalt, concrete, pavers, or gravel surfaces. It distributes loads across the sub-grade, improves drainage, and prevents rutting or heaving. The most common materials are dense-graded crushed stone, compacted gravel, caliche, and recycled asphalt millings. A well-constructed road base is usually 4 to 8 inches (10 to 20 cm) thick for residential driveways and up to 12 inches (30 cm) or more for roads that carry heavy equipment.
How the road base calculator works
The calculator starts with your three dimensions - length, width, and depth - and converts them all to metres regardless of the unit you choose. It then multiplies length by width to find the surface area, and multiplies that by depth to get the raw volume in cubic metres. Because loose aggregate compacts when placed and rolled, you must order more than the finished volume requires. The compaction allowance (10-20% is typical) accounts for that reduction in thickness. The waste and overrun allowance (5-10%) covers trimming, spillage, and variation in sub-grade level. The calculator multiplies the raw volume by both factors to give you the amount to actually order. It then multiplies that adjusted volume by the material bulk density to estimate the total weight in US short tons and metric tonnes, which is how most suppliers price aggregate.
Choosing the right depth
The required depth depends on the traffic load and the strength of the existing sub-grade. Pedestrian paths and light driveways typically need 4 inches (100 mm) of compacted base. Residential driveways with passenger-vehicle traffic normally require 6 inches (150 mm). Roads used by commercial vehicles or heavy equipment typically need 8 to 12 inches (200 to 300 mm), sometimes placed in two compacted lifts. If your sub-grade is soft clay or poorly drained soil, increase depth by 2 to 4 inches or add a geotextile fabric separator beneath the base layer to prevent sub-grade fines from pumping up into the aggregate.
Tips for ordering and placing road base
Order from a local quarry or aggregate supplier and ask for the delivered cost per ton - prices vary widely by region and material. Confirm whether the price is per US short ton (2,000 lb) or metric tonne (2,205 lb) to avoid ordering too little. For best compaction, the material should be within 1-2% of its optimum moisture content; ask your supplier what that is for the specific gradation. Place in lifts of no more than 6 inches (150 mm) and compact with a plate compactor or roller after each lift. Check density with a nuclear gauge or Proctor test if the project requires engineered compaction specifications.
Common road base materials and typical densities
| Material | Bulk density (kg/m3) | Typical use | Notes |
|---|---|---|---|
| Gravel - loose | 1,520 | Drainage, sub-base | High drainage capacity |
| Gravel - dense graded (DGA) | 1,680 | Road base, driveways | Self-compacting when wet |
| Crushed stone / limestone | 1,600 | Road base, paths | Excellent compaction |
| Crushed granite | 1,650 | High-traffic roads | Hard, durable surface |
| Road base (compacted) | 2,080 | Road base, parking lots | Measured after compaction |
| Decomposed granite | 1,570 | Paths, light driveways | Dust binder needed |
| Sand - dry | 1,600 | Leveling layer | Poor load bearing alone |
| Sand - wet packed | 1,905 | Bedding layer | More stable than dry |
| Pea gravel | 1,520 | Drainage, decorative | Difficult to compact |
| River rock | 1,600 | Drainage, aesthetics | Not ideal for traffic |
| Asphalt millings | 1,218 | Recycled base layer | Binds when heated by sun |
| Caliche | 1,700 | Southwest US road base | Natural calcium carbonate |
Bulk densities vary by moisture content, gradation, and source. Confirm with your supplier for accurate ordering.
Frequently asked questions
How much road base do I need for a 12x100 foot driveway at 6 inches deep?
A 12 x 100 ft area at 6 inches depth has a raw volume of 1,200 cubic feet, which equals about 44.4 cubic yards. Adding a 15% compaction allowance and 5% waste brings the order quantity to roughly 53 cubic yards. At a typical road base density of 2,080 kg/m3 that is approximately 84 US short tons. Use this calculator with length 100 ft, width 12 ft, depth 6 in, and material "Road base (compacted)" to verify with your specific adjustments.
What is the difference between cubic yards and tons for road base?
Cubic yards measure volume; tons measure weight. To convert between them you need the bulk density of the material. Dense-graded road base typically weighs about 1.4 to 1.6 short tons per cubic yard in its loose or lightly compacted state. Suppliers sell by the ton, so the calculator converts your volume to tons using the material density you select. Always confirm the density with your specific supplier because it can vary by source and moisture content.
Why do I need a compaction allowance?
Aggregate is typically delivered and spread in a loose state, then compacted by a roller or plate compactor. During compaction, air voids are eliminated and the material densifies, reducing the layer thickness by 10 to 20% depending on the gradation and moisture. If you order only enough material to fill the final compacted volume, you will run short. A 15% compaction allowance means ordering 1.15 cubic yards for every cubic yard of finished, compacted base.
How thick should road base be for a driveway?
For a standard residential driveway that carries passenger cars and light SUVs, 4 to 6 inches (10 to 15 cm) of compacted road base is typical. If the sub-grade is soft or poorly drained, use 6 to 8 inches. For a driveway that will regularly carry delivery trucks, concrete mixers, or heavy equipment, plan for at least 8 to 12 inches placed in two lifts of 4 to 6 inches each.
What is the best material for a gravel driveway base?
Dense-graded aggregate (DGA) or crusher run (also called road base) is the most widely recommended material because its mix of large, medium, and fine particles locks together under compaction. Crushed limestone and crushed granite are also excellent. Avoid round gravel or pea gravel for the base layer - the rounded particles do not interlock and can shift under load. A layer of DGA topped with a finer crushed stone finish layer is a common and durable approach for residential driveways.
How do I convert tons to cubic yards for road base?
Divide the weight in pounds by the material bulk density in pounds per cubic foot, then divide by 27 (the number of cubic feet in a cubic yard). For road base at roughly 125 lb per cubic foot (2,000 kg/m3), each cubic yard weighs about 3,375 lb or about 1.69 short tons. So 10 tons / 1.69 = about 5.9 cubic yards. Because density varies by material, use the calculator above and select your specific material for a more accurate conversion.