Excavation Calculator
Calculates the cubic yards of soil to be removed and the total excavation cost for foundations, trenches, or grading projects. Use it when getting contractor quotes or planning equipment rental.
About this calculator
Excavation volume is measured in cubic yards because that is the unit used to price hauling, fill, and machine time. The formula is: cost = (length × width × depth / 27) × soilTypeFactor × costPerCubicYard. Dividing by 27 converts cubic feet to cubic yards (since 1 yd³ = 27 ft³). The soil type factor adjusts cost for the difficulty of excavation: loose sandy soil is assigned a factor near 1.0, while dense clay or rocky ground carries a higher factor reflecting slower digging and greater equipment wear. Cost per cubic yard includes machine time, operator labor, and sometimes haul-off fees. Note that excavated soil swells by 10–30% in volume (called swell factor) when removed, which affects trucking requirements even though it does not change the in-ground volume calculation.
How to use
You are excavating a foundation 30 ft long × 20 ft wide × 4 ft deep in average soil (factor = 1.2) at $25 per cubic yard. Volume = 30 × 20 × 4 / 27 = 2,400 / 27 ≈ 88.9 cubic yards. Cost = 88.9 × 1.2 × $25 = 88.9 × 30 = $2,667. You would budget approximately $2,667 for this excavation. For rocky ground (factor = 1.5), the same dig would cost $25 × 88.9 × 1.5 = $3,334 — a 25% increase.
Frequently asked questions
How do I calculate cubic yards of excavation for a foundation?
Multiply the length, width, and depth of the excavation in feet, then divide by 27 to convert to cubic yards. For example, a 40 ft × 25 ft × 3 ft dig yields 40×25×3/27 = 111 cubic yards. Always add 10–15% extra to account for uneven walls and sloping sides that are required for worker safety (known as cut slopes or shoring). The cubic yard figure is what you will give to an excavation contractor for a quote, and it determines how many dump-truck loads are needed for haul-off.
Why does soil type affect excavation cost so much?
Different soil types require different equipment, digging speeds, and effort levels, all of which drive up or down the cost per cubic yard. Loose sandy or loamy soil can be scooped quickly with a standard excavator, keeping costs low. Dense clay is cohesive and sticky, slowing the bucket and increasing cycle times. Rock requires breaking with a hydraulic hammer or blasting before removal, which can triple or quadruple the cost compared to soil. Knowing your soil classification before requesting bids helps you evaluate whether contractor quotes are reasonable.
What is the difference between cut volume and fill volume in excavation?
Cut volume is the amount of soil removed from the ground, measured in its natural, undisturbed state (bank cubic yards). Fill volume is the amount of soil needed to fill a void or raise a grade, measured in its compacted state. When soil is excavated it loosens and expands by 10–30% (swell), and when it is compacted as fill it shrinks by 5–15% (shrinkage). This means one bank cubic yard of cut does not equal one compacted cubic yard of fill. Earthwork contractors balance cut and fill on a site to minimize the cost of hauling excess material away or importing fill.