How the Backfill Dirt Calculator Works
The Backfill Dirt Calculator estimates the amount of material needed to refill a trench, hole, sloped area, or excavation. It converts the volume into cubic feet, cubic yards, approximate weight, and optional cost.
Backfill Volume Formula
For a rectangular excavation:
For a triangular section:
For a sloped area using average depth:
Cubic Feet to Cubic Yards
Backfill material is often ordered in cubic yards:
Typical Material Densities
| Material | Approximate density |
|---|---|
| Topsoil | 80 lb/ft³ |
| Sand | 100 lb/ft³ |
| Gravel | 120 lb/ft³ |
| Clay | 95 lb/ft³ |
Why Add Compaction and Waste Allowance?
Soil and aggregate volume changes during hauling, placing, wetting, and compaction. Adding an allowance helps avoid ordering too little material.
- Compaction allowance: accounts for settlement and densification.
- Waste allowance: accounts for spillage, uneven excavation, and delivery variation.
- Moisture content: can change both volume and weight.
Frequently Asked Questions
How much dirt do I need for backfill?
Calculate the excavation volume, then add compaction and waste allowance. The result can be converted to cubic yards for ordering.
How many cubic feet are in one cubic yard?
One cubic yard equals 27 cubic feet.
Should I order extra backfill material?
Yes. Ordering 5% to 20% extra is often useful depending on compaction, settlement, and site conditions.
Can I use gravel instead of dirt?
Yes, but gravel has a different density and drainage behavior. Use the material type that matches your project.