TryBuildCalcFrench Drain Gravel Calculator (Drainage Stone Weight & Volume)
Calculate gravel for a French drain.
🕒 Last updated: August 20, 2026
Inputs
Primary use: French drains, soakaways
ℹ️Auto-filled by gravel type. Use supplier-tested density for large orders.
ℹ️Enter your supplier rate. Market price is not estimated.
9.00 m³
317.83 ft³ • 11.77 yd³ • Area 15.00 m²
Single Size Drainage Gravel (20mm)
13,320 kg
13.32 tonnes
13,986 kg
13.99 tonnes • +5% wastage included
Standard truck (10T)
1.4 loads
2 full load(s)
Single Size Drainage Gravel (20mm)
Open-graded drainage gravel. Use 0% compaction so water can move freely through the layer.
Input Shape: Rectangle
Density Used: 1,480 kg/m³
Layer Use: drainage
Standards: ASTM D448 / BS EN 13242 / IS 383
Gravel Project Visualizations
Weight Breakdown and Comparison
Typical Gravel Depth Guide
Area Shape Check
French drain gravel estimate
Clean drainage stone should preserve void space around the perforated pipe.
Do not apply dense-base compaction assumptions to an open-graded drain layer.
- 20 mm drainage gravel selected.
- Default trench: 30 m × 0.5 m × 0.6 m.
- Compaction set to 0%.
How Is Gravel Weight Calculated?
Gravel weight is calculated by first finding the project volume, then adjusting for compaction, moisture, wastage, and delivery units. Unlike sand, gravel does not normally require bulking correction, but compacted road base and driveway layers often need extra loose material.
Step 1 — Calculate Project Volume
Rectangle / Slab / Driveway = Length × Width × Depth
Circle = π × (Diameter ÷ 2)² × Depth
L-shape = (Area A + Area B) × Depth
Triangle = 0.5 × Base × Height × Depth
All dimensions are converted to metres before volume is calculated. The result is the finished volume in cubic metres.
Step 2 — Convert Volume to Common Site Units
Cubic feet = m³ × 35.3147
Cubic yards = m³ ÷ 0.764555
Brass = Cubic feet ÷ 100
These conversions help users compare supplier quotes in cubic metres, cubic feet, cubic yards, or brass.
Step 3 — Apply Compaction Factor
Compaction Allowance = Finished Volume × (Compaction % ÷ 100)
Loose Volume = Finished Volume + Compaction Allowance
Compacted gravel layers such as road base, driveway base, GSB, and dense graded aggregate require extra loose material. Drainage gravel or decorative gravel may use 0% compaction.
Step 4 — Convert Loose Volume to Dry Weight
Dry Weight (kg) = Loose Volume (m³) × Bulk Density (kg/m³)
Dry Weight (tonnes) = Dry Weight (kg) ÷ 1000
Bulk density is the mass of gravel per cubic metre, including air gaps between stones. It changes by gravel type, size, grading, shape, and source.
Step 5 — Apply Moisture Factor
Moisture Adjusted Weight = Dry Weight × Moisture Factor
Damp or wet gravel weighs more than dry gravel. Moisture adds mass, but gravel does not expand like damp sand, so sand-style bulking correction is not used.
Step 6 — Add Wastage
Wastage Quantity = Moisture Adjusted Weight × (Wastage % ÷ 100)
Order Quantity = Moisture Adjusted Weight + Wastage Quantity
Wastage covers unloading loss, spreading variation, handling loss, irregular edges, and material left on the vehicle or site surface.
Step 7 — Convert to Delivery Units and Cost
Tonnes = Order Quantity (kg) ÷ 1000
Bags = Order Quantity (kg) ÷ Bag Size (kg), rounded up
Loads = Order Quantity (kg) ÷ Vehicle Capacity (kg), rounded up
Cost = Tonnes × Price per Tonne
The final quantity is converted into practical ordering units such as tonnes, bags, and delivery loads.
Real-World Gravel Weight Calculation Example
This example uses the active calculator inputs and follows the same seven steps from the formula section. Each table explains what value is used, why it is used, and how the result is calculated.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Gravel type | Single Size Drainage Gravel (20mm) | Used to select practical bulk density |
| Shape | Rectangle | Decides which volume formula is used |
| Length | 30 m | Length of the gravel area |
| Width | 0.5 m | Width of the gravel area |
| Depth / Thickness | 600 mm | Gravel layer thickness |
| Bulk density | 1,480 kg/m³ | Converts loose gravel volume into dry weight |
| Compaction factor | 0% | Adds extra loose material before compaction |
| Moisture condition | DRY / factor 1.00 | Adjusts dry weight for damp or wet gravel |
| Wastage factor | 5% | Allows for unloading, spreading, and handling loss |
Step 1 — Calculate Project Volume
First, the calculator converts the project dimensions into metres and calculates the finished gravel volume in cubic metres. This is the compacted or final space that the gravel must fill.
| Shape | Formula / Substitution | Finished Volume |
|---|---|---|
| Rectangle | 30.000 × 0.500 × 0.600 | 9.000 m³ |
Step 2 — Convert Volume to Common Site Units
The finished volume is converted into common supplier units. This helps compare quotes given in cubic feet, cubic yards, brass, or cubic metres.
| Unit | Formula / Substitution | Result |
|---|---|---|
| Cubic feet | 9.000 × 35.3147 | 317.83 ft³ |
| Cubic yards | 9.000 ÷ 0.764555 | 11.77 yd³ |
| Brass | 317.83 ÷ 100 | 3.18 brass |
Step 3 — Apply Compaction Factor
Compacted gravel occupies less volume after rolling or tamping. The calculator adds compaction allowance to estimate how much loose gravel should be ordered.
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Compaction allowance | 9.000 × (0 ÷ 100) | 0.000 m³ |
| Loose volume | 9.000 + 0.000 | 9.000 m³ |
Step 4 — Convert Loose Volume to Dry Weight
Loose volume is converted to dry gravel weight using bulk density. Bulk density includes the air voids between gravel particles, so it is suitable for ordering and site quantity estimation.
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Dry weight | 9.000 × 1,480 | 13,320 kg |
| Dry weight in tonnes | 13,320 ÷ 1000 | 13.32 tonnes |
Step 5 — Apply Moisture Factor
Moisture increases gravel weight. This step adjusts the dry weight for damp or wet gravel. Gravel does not use sand-style bulking correction.
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Moisture adjusted weight | 13,320 × 1.00 | 13,320 kg |
| Adjusted weight in tonnes | 13,320 ÷ 1000 | 13.32 tonnes |
Step 6 — Add Wastage
Wastage is added to the moisture-adjusted weight to cover site losses, spreading variation, irregular edges, and unloading loss.
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Wastage quantity | 13,320 × (5 ÷ 100) | 666 kg |
| Order quantity | 13,320 + 666 | 13,986 kg |
Step 7 — Convert to Delivery Units and Cost
Finally, the order quantity is converted into tonnes, bags, delivery loads, and cost so it can be used for actual procurement.
| Calculation | Formula / Substitution | Result |
|---|---|---|
| Tonnes | 13,986 ÷ 1000 | 13.99 tonnes |
| Delivery loads | 13,986 ÷ 10,000 | 1.40 loads → plan 2 full load(s) |
Therefore, the required gravel order quantity is 13,986 kg, or 13.99 tonnes, after compaction, moisture adjustment, and wastage. Based on the selected delivery capacity, plan for 2 full load(s).
Calculator Limitations & Assumptions
- Bulk density values are typical ranges. Gravel can vary by 5-10% between quarry sources because of parent rock, grading, and particle shape. For critical or large projects, obtain a tested bulk density under ASTM C29, BS EN 1097-3, or IS 2386 Part III.
- Compaction factors are approximate. Actual volume reduction depends on gradation, sub-grade bearing capacity, equipment, moisture, and number of passes. A geotechnical engineer should specify structural fill and road-base compaction.
- L-shape and triangle modes assume simple geometry and a common depth. Divide shapes with varying depths, tapered widths, or multiple sections into separate calculations and add the totals.
- This calculator estimates material quantity only. It does not determine bearing capacity, pavement design, layer thickness, or suitability for expected vehicle loads. These should be specified by an engineer.
- Depth recommendations are typical residential guidance. Flat-roof ballast, railway ballast, engineered filter media, and other specialist applications require project-specific engineering specifications.
- Gravel does not bulk like sand. The wet adjustment of about 5-12% represents surface water and absorbed moisture only. For most ordinary ordering, dry weight is an adequate basis.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.