Two layers, two jobs
The standard driveway build-up is a base course of dense-graded aggregate — crushed stone with fines, often called road base, crusher run or DGA — compacted in lifts to form a load-bearing platform, topped with a thinner surface layer of smaller, cleaner gravel that sheds water and provides the running surface. Guidance for gravel roads and driveways consistently attributes most surface failures — rutting, potholes, stone migration — to a missing or inadequate base rather than to the surface stone itself.
Base courses for residential driveways are commonly in the region of 10–20 cm compacted depth (deeper for soft subgrades or heavy vehicles), while the surface layer is typically about 5 cm — it's a wearing course, not a structural one, so it stays thin and relies on the base beneath it for strength.
The formula: volume to tonnes
Each layer's volume equals the driveway area (length × width) multiplied by that layer's depth in meters. The volume is then converted to weight using the layer's typical compacted density: 1,920 kg/m³ for dense-grade base aggregate and 1,680 kg/m³ for surface gravel — published typical values; a quarry's ticket density for the specific product takes precedence for a final order.
- Area (m²) = Length × Width
- Base tonnes = Area × (Base depth ÷ 100) × 1,920 ÷ 1,000
- Surface tonnes = Area × (Surface depth ÷ 100) × 1,680 ÷ 1,000
Worked example: a 15 m × 3 m driveway
A 15 m × 3 m driveway (45 m²) with a 15 cm base and 5 cm surface layer needs 45 × 0.15 = 6.75 m³ of base, which is 6.75 × 1,920 ÷ 1,000 = 12.96 tonnes. The surface layer needs 45 × 0.05 = 2.25 m³, which is 2.25 × 1,680 ÷ 1,000 = 3.78 tonnes. Total material volume is 9 m³, weighing roughly 16.7 tonnes across both layers.
| Layer | Volume | Density | Weight |
|---|---|---|---|
| Base (15 cm) | 6.75 m³ | 1,920 kg/m³ | 12.96 t |
| Surface (5 cm) | 2.25 m³ | 1,680 kg/m³ | 3.78 t |
| Total | 9 m³ | — | ≈ 16.74 t |
Compacted vs. loose depth, and drainage
The depths in this calculation are compacted depths, not the depth of loose material as it's dumped and spread. Dense-grade base compacts by roughly 10–20% from its loose spread depth, so material is typically spread thicker than the target and compacted down in lifts of about 10 cm or less to reach the intended finished depth — ordering by the compacted-depth figure alone can understate how much loose material needs to be delivered and spread.
A flat gravel surface holds puddles and fails early; a crown or cross-slope, commonly around 2–5% on gravel surfaces, is what actually sheds water off the driveway. Soft or clay subgrades may also need a deeper base, a geotextile separation fabric between subgrade and base, or both — conditions a soils-aware contractor or local road-authority guidance should confirm.
Häufig gestellte Fragen
How deep should gravel be on a driveway?
A common residential build-up is a compacted dense-grade base of about 10–20 cm topped with roughly 5 cm of surface gravel. Soft subgrades and heavier vehicles call for a deeper base.
How many tonnes of gravel do I need for a 15 by 3 meter driveway?
With a 15 cm compacted base and a 5 cm surface layer, a 45 m² driveway needs about 12.96 tonnes of dense-grade base aggregate and about 3.78 tonnes of surface gravel — roughly 16.7 tonnes of material in total.
What is the difference between road base and surface gravel?
Road base (dense-graded aggregate, crusher run) contains crushed stone in a range of sizes down to fines, which lock together under compaction into a load-bearing layer. Surface gravel is smaller, more uniform stone chosen to shed water and provide a stable running surface; it relies on the base beneath it for strength.
Do I need fabric under a gravel driveway?
Geotextile separation fabric between the subgrade and the base is commonly recommended on soft, wet or clay soils, where it stops the aggregate from being pushed down into the subgrade and losing thickness over time. On firm, well-drained subgrades it is often omitted.
How much does a cubic meter of gravel weigh?
Compacted dense-grade base aggregate is typically taken as about 1,920 kg/m³ and surface gravel as about 1,680 kg/m³, though actual figures vary with gradation, moisture and stone type. Quarries publish product-specific conversion factors for final orders.
Quellenangaben
- US Federal Highway Administration (FHWA) / South Dakota LTAP — Gravel Roads: Maintenance and Design Manual: layered construction, crown/cross-slope and surface-gravel gradation guidance.
- AASHTO M147 — Standard Specification for Materials for Aggregate and Soil-Aggregate Subbase, Base, and Surface Courses: dense-graded aggregate base materials.
- Aggregate producer technical data (quarry conversion charts) — typical loose and compacted densities in tonnes per cubic meter by product.