Excavation Volume Calculator
Calculate the volume of earth to be removed for a rectangular foundation or trench excavation. Use it to estimate haulage truck loads, disposal costs, and excavation plant hours before breaking ground.
About this calculator
For a rectangular pit or trench, the volume of material to be excavated is simply: Volume = length × width × depth. All dimensions must be in metres, giving a result in cubic metres (m³). In practice, the neat excavation volume is always increased by a bulking factor — loose soil occupies 20–40% more volume than compacted in-situ material, depending on soil type. Clay bulks at around 25–30%, while rock can bulk by 30–50%. Contractors use the in-situ volume to size the excavation and the bulked volume to size the disposal fleet. If sloped sides (batters) are required for stability, the actual excavation will be larger than the neat rectangle; for sloped cuts, a prismatoid formula is more accurate.
How to use
A strip foundation is 12 m long, 1.2 m wide, and 1.0 m deep. Volume = 12 × 1.2 × 1.0 = 14.4 m³ (in-situ). With a bulking factor of 25% for medium clay, the loose volume loaded onto trucks = 14.4 × 1.25 = 18.0 m³. A standard 6 m³ tipper truck carries roughly 3 loads to dispose of the spoil. If topsoil (0.3 m deep) is stripped separately and stockpiled for reinstatement, it accounts for 12 × 1.2 × 0.3 = 4.32 m³ and should be calculated independently from the structural excavation below.
Frequently asked questions
How do I account for bulking factor when calculating excavation volume for haulage?
Bulking factor converts in-situ (bank) volume to loose volume, which is what fills a truck. Multiply the calculated excavation volume by (1 + bulking percentage). Typical values are: topsoil 25%, sandy soil 10–15%, clay 25–30%, chalk 33%, soft rock 40%, hard rock 50%. Always confirm the bulking factor with a geotechnical report or at minimum a soil classification from trial pits. Underestimating the factor means under-ordering trucks and delays on-site.
What is the difference between cut volume and fill volume in earthwork calculations?
Cut volume is the material excavated and removed; fill volume is the material placed and compacted to form embankments or backfill. They are not interchangeable by weight or volume because of bulking (cut to loose) and shrinkage (loose to compacted fill). Compacted fill typically occupies 85–95% of its loose volume. A mass haul diagram balances cuts and fills across a site to minimise double-handling. For small foundation excavations this distinction matters mainly for backfill estimation around the footing.
When should I use a prismatoid formula instead of length × width × depth for excavation volume?
Use the prismatoid (end-area or Simpson's rule) method when the excavation has sloped sides (batters), non-uniform cross-sections, or when ground level varies significantly across the site. For a trapezoidal cross-section with base width B, top width T, and depth D, the area = (B + T)/2 × D, then multiply by length. Sloped sides are required by occupational safety regulations when excavating deeper than 1.2–1.5 m in most jurisdictions to prevent collapse, so a simple rectangle will underestimate the actual removed volume in those cases.