Backfill Volume Calculator
A backfill volume calculator determines how much fill material is needed to restore an excavation after a foundation, pipe, or other structure has been installed. Backfill volume is not the same as excavation volume: you must subtract the volume occupied by the structure from the total pit volume to find the net space that needs to be filled. This tool computes the total excavation volume, subtracts the structure volume you specify, applies a shrinkage factor to account for compaction, and calculates the loose volume of material to order. This ensures you purchase the right amount of fill without over-ordering or running short before the trench is closed.
Backfill volume formula
Excavation Vol (cu yd) = (L x W x D) / 27
Structure Vol (cu yd) = (Ls x Ws x Ds) / 27
Net Backfill = Excavation Vol - Structure Vol
Loose Volume = Net Backfill / (1 - Shrinkage% / 100)
The shrinkage factor accounts for compaction: loose material reduces in volume when placed and compacted. Order the loose volume from your supplier.
Frequently asked questions
What is backfill?
Backfill is the material used to refill an excavation after a foundation, utility, or structure has been installed. Suitable backfill materials include native soil (if approved), granular fill, crushed stone, or engineered fill. Backfill must be placed and compacted in lifts to achieve specified density.
How is backfill volume calculated?
Backfill volume equals the total excavation volume minus the volume occupied by the structure or buried element. For a wall footing, subtract the footing volume from the pit volume. The result is the net volume of material needed to refill around the structure.
What compaction standard is required for backfill?
Most structural backfill requires 95% of the maximum dry density as determined by ASTM D1557 (Modified Proctor) or ASTM D698 (Standard Proctor). Utility trench backfill may require 90-95% depending on location. Always follow the project specifications and engineer's requirements.
How many tons of fill do I need per cubic yard?
Compacted fill density varies by material: sand is about 1.3-1.5 tons/cy, clay 1.4-1.6 tons/cy, crushed stone 1.5-1.7 tons/cy, and topsoil 1.1-1.3 tons/cy. Divide cubic yards of fill by the material density to estimate tons to purchase.
What is a shrinkage factor in backfill?
Shrinkage (or compaction factor) is the reduction in volume when loose fill is compacted. Loose material must be purchased in greater quantity than the net backfill volume to account for this reduction. Typical shrinkage: sand 15-20%, clay 10-15%, crushed stone 5-10%.
Official sources
- ASTM International: ASTM D1557 - Standard Test Methods for Laboratory Compaction Characteristics of Soil.
- U.S. Army Corps of Engineers: USACE EM 1110-1-1904 - Settlement Analysis.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.