| Scenario | Dimensions | Depth | Factors | Result summary |
|---|---|---|---|---|
| Raised bed drainage layer | 2.4 m × 1.2 m | 0.08 m | Compaction 1.08, Waste 10% | Volume ≈ 0.27 m³, Weight ≈ 0.43 t (pea gravel) |
| French drain trench | 12 m × 0.25 m | 0.15 m | Compaction 1.10, Waste 12% | Volume ≈ 0.55 m³, Weight ≈ 0.92 t (crushed stone) |
| Circular planter base | Diameter 1.0 m | 0.10 m | Compaction 1.05, Waste 8% | Volume ≈ 0.09 m³, Weight ≈ 0.14 t (river rock) |
These are examples only. Real projects vary by soil, drainage fabric, and compaction.
- Area = Length × Width (rectangle/trench), or π × (Diameter/2)² (circle)
- Compacted Volume = Area × Depth
- Loose Volume = Compacted Volume × Compaction Factor
- Total Volume = Loose Volume × (1 + Waste%/100)
- Weight = Total Volume × Density
- Bags = ceil(Weight ÷ Bag Size) (optional)
- Select your unit system and project type.
- Enter the main dimensions and the gravel depth.
- Pick a gravel type, or set a custom density.
- Adjust compaction and waste to match your method.
- Optionally add bag size and pricing for estimates.
- Press Calculate, then download CSV or PDF if needed.
Depth planning for healthy root zones
Drainage gravel works best when depth matches soil texture and rainfall. For raised beds, 5–10 cm supports aeration without starving roots. For French drains, 10–20 cm improves storage and flow. Sandy soils often need less gravel, while clay benefits from deeper layers and clear outlets. This calculator lets you test depths quickly, then compare volume and delivery weight before you buy.
Compaction and settlement adjustments
Gravel settles after watering, foot traffic, or tamping, especially in narrow trenches. A compaction factor of 1.05–1.15 usually covers this change. If you compact in lifts or expect heavy loading, choose 1.12–1.18. The tool separates compacted volume from loose volume, helping you order enough material the first time.
Choosing the right density for your gravel
Rounded pea gravel packs differently than angular crushed stone, and lightweight aggregates can be dramatically lighter. Density drives the weight estimate, bag counts, and transport needs. Select a preset gravel type or enter a custom density from your supplier’s ticket. Moisture can raise delivered weight; use supplier data when possible. Accurate density reduces surprises at checkout and during handling.
Overage, waste, and real-world site conditions
Uneven trenches, soft subgrade, and spillage can consume more aggregate than drawings suggest. Adding 5–15% overage is common for small projects, while long trenches may need extra for shaping and bedding. If you include pipe bedding and side backfill, treat the trench width as the full gravel zone, not the pipe diameter. The waste setting builds a buffer into total volume, so your final order stays practical and reliable.
Cost comparisons and purchasing strategy
Suppliers price gravel by tonne, cubic yard, or cubic meter. This calculator converts your design into each unit, so you can compare quotes fairly. Use bag size when buying retail packs, or add a bulk price for an estimate. Many deliveries round up to minimum loads, so check truck limits and access gates. Pair the results with delivery access and wheelbarrow distance for smoother planning.
FAQs
1) Should I choose pea gravel or crushed stone for drains?
Crushed stone locks together and supports pipes well. Pea gravel flows easily but can shift. Choose crushed stone for trenches and structural backfill, and use pea gravel for decorative drainage layers where stability is less critical.
2) What compaction factor should I use?
Use 1.05–1.10 for lightly settled gravel and 1.10–1.18 when you tamp in layers or expect traffic. If you are unsure, start with 1.10 and adjust after a small test section.
3) Why does density change the result so much?
Volume stays the same, but weight depends on density. Heavier stone increases delivery weight, bag counts, and cost per tonne. Lightweight aggregates reduce weight, which can help rooftop planters or areas with load limits.
4) How much waste or overage is reasonable?
For small beds, 5–10% is typical. For trenches with uneven sides or soft bases, 10–15% is safer. Increase overage if you expect spillage, deep bedding, or irregular excavation.
5) Can I estimate bags accurately?
Yes, if bag weight matches the product and moisture is consistent. Enter the bag size shown on the packaging. For mixed-size rock, expect slight variation, and round up one extra bag for patching and leveling.
6) How do I compare supplier quotes fairly?
Ask each supplier for pricing per tonne and per volume unit, plus delivery fees. Use this tool to convert your project into m³ and yd³. Compare totals using the same unit and include minimum-load rules.