Excavation Calculator

Estimate soil volume for a trench or foundation

This excavation calculator estimates how much soil must be removed for a trench or a rectangular foundation excavation. Enter the length, depth, and width, then add the number of matching excavations. For a trench, use bottom and top widths to account for sloped sides. For a foundation, enter the footing or foundation width and the working space needed around it.

The result separates bank volume from loose volume. Bank volume is the soil in the ground before digging. Excavated soil usually takes up more space after it is loosened, so a swell allowance estimates the loose volume that may need hauling. You can also estimate truck loads and an optional removal cost from the loose volume.

This is a quantity planning tool, not a trench safety plan or engineering design. Soil type, groundwater, access, slope stability, utilities, and local rules affect how an excavation should be carried out. Confirm dimensions and safety requirements with a qualified professional before digging.

How to use the excavation calculator

Choose Imperial or Metric and select trench or foundation. Enter the excavation length, depth, and count. For a trench, enter the width at the bottom and the width at the top. The calculator uses the average of those widths as a simple trapezoidal cross section. If the sides are vertical, set the top width equal to the bottom width.

For a foundation excavation, enter the foundation width and the working space on each side. Working space increases the excavation width and length, allowing room around the structure. Enter zero if the excavation dimensions already include that space. Add overdig only when you need to account for extra depth or uneven excavation beyond the measured dimensions.

Enter the soil swell percentage based on the material or a contractor's estimate. Add the truck capacity in cubic yards or cubic metres to estimate the number of loads. An optional price per volume unit gives a basic hauling or removal subtotal. Rates differ, so enter the rate that applies to the same volume unit shown by the calculator.

Excavation volume formula

A rectangular excavation uses length multiplied by width and depth. A trench with sloped sides has a trapezoid-shaped cross section. Its average width is the top width plus bottom width divided by two. Multiply that average width by depth and trench length. Repeated excavations are multiplied by their count. Overdig is applied as a percentage after the basic volume is calculated.

• Rectangular volume = length × width × depth
• Trench average width = (bottom width + top width) ÷ 2
• Trench volume = length × average width × depth
• Foundation excavation width = foundation width + 2 × working space
• Bank volume = basic volume × count × (1 + overdig %)
• Loose volume = bank volume × (1 + soil swell %)
• Truck loads = loose volume ÷ truck capacity, rounded up

Worked example: trench excavation

Consider a trench that is 60 feet long and 4 feet deep. Its bottom width is 2 feet and top width is 3 feet. Average width is (2 + 3) ÷ 2, or 2.5 feet. The bank volume is 60 × 4 × 2.5, which equals 600 cubic feet, or about 22.2 cubic yards before overdig.

Add 5% overdig and the estimated bank volume becomes about 23.3 cubic yards. If the soil swell allowance is 25%, the loose volume is roughly 29.2 cubic yards. With trucks that hold 10 cubic yards, the calculator rounds up to 3 loads. Actual truck payload and usable capacity may be limited by weight, local road rules, or the material's moisture content.

The calculation assumes a uniform trench width and depth. A real trench may vary because of soil conditions, equipment, bends, utility crossings, and safe side slopes. Use this example to understand the calculation, then check the job measurements and hauling plan before booking trucks.

Bank cubic yards and loose soil volume

Bank volume describes undisturbed soil in its natural position. It is often used to describe the excavation quantity before digging. Loose volume describes the soil after it has been broken up and placed in a truck or stockpile. Soil particles no longer fit together as tightly, so the loose volume is normally larger.

The difference between bank and loose volume is called swell. The amount varies with soil type, moisture, compaction, rock content, and excavation method. Clay, sand, gravel, and mixed fill do not all swell by the same amount. The calculator does not identify the soil; use a project-specific percentage from a geotechnical report, contractor, or hauling provider when possible.

Choosing a soil swell allowance

A swell allowance helps estimate how much loose material will be hauled away or stored after excavation. It should reflect the material being dug, not a generic value chosen without context. Ask a local excavation contractor or disposal site what swell factor they use for similar ground. If a quote already includes a swell factor, avoid applying another allowance to the same quantity.

Moisture can increase soil weight and change how it handles, while breaking up compacted soil changes the volume. Rock may need a different treatment from ordinary soil. A single percentage is only a planning estimate for mixed material. For large jobs, use measured truck tickets or a quantity surveyor's takeoff to reconcile actual loads with the estimated bank volume.

Trench width, depth, and sloped sides

Trench dimensions may be specified at the bottom, top, or by a typical width. If trench sides slope outward, top width is greater than bottom width. This calculator estimates the cross section with the average of top and bottom widths. It is a simple trapezoid estimate and assumes the same slope and depth along the full length.

If the trench has vertical sides, enter the same value for top and bottom width. If the trench changes width or depth, split it into separate estimates and add the volumes. Do not make the trench narrower or steeper than allowed for the ground and work conditions. A volume calculator cannot determine whether trench walls are stable or safe.

Foundation excavation and working space

A foundation excavation often needs room beyond the footing or wall dimensions for forms, drainage, waterproofing, inspection, and safe construction access. Enter the planned working space on each side. The calculator adds twice that amount to the foundation width and length, because space is included on both opposing sides.

For example, a 20-foot foundation length with 2 feet of working room at each end gives a 24-foot excavation length. The same addition applies across the width. If the dimensions you enter already describe the full excavation, set working space to zero to avoid counting it again. Confirm the required clearance with the design and construction team.

Overdig and excavation tolerance

Overdig is extra excavation beyond the nominal dimensions. It may account for uneven ground, equipment tolerances, cleanup at the bottom, or a specified construction allowance. The calculator adds the percentage to the geometric volume. Overdig is not a substitute for working space: working space changes the excavation footprint, while overdig adds a percentage to the total quantity.

Use an allowance only when it reflects the project plan. Too much overdig can increase disposal costs and may require additional fill or concrete. If a foundation detail sets exact excavation limits, follow that design rather than adding a default percentage. If the ground is irregular, estimate separate areas or have the excavation plan reviewed by the project professional.

Estimate truck loads and soil removal

Truck loads are estimated by dividing loose soil volume by the truck capacity you enter and rounding up to a whole load. A 29 cubic yard loose volume with a 10 cubic yard capacity requires three loads by volume. The result is only an approximate load count because a truck may reach its legal weight limit before its box is full.

Soil moisture, density, access, loading equipment, and disposal facility rules can change the hauling plan. Confirm the truck's rated payload and the material acceptance requirements with the hauler. Some sites charge by weight, some by volume, and some have minimum fees. Do not assume that the calculator's cubic yard estimate is the same as the billable quantity.

Excavation cost estimate

The optional cost estimate multiplies loose volume by the price per cubic yard or cubic metre that you enter. It can help with an early budget for trucking or soil removal. The actual invoice may use truck hours, weight tickets, machine hours, disposal fees, mobilization, or a minimum charge instead of a simple volume rate.

Excavation cost also depends on access, depth, soil conditions, groundwater, utilities, shoring, equipment size, haul distance, and disposal requirements. The calculator does not include these items, imported fill, compaction, equipment rental, permits, testing, or restoration. Request a site-specific quote for a more reliable project budget.

Converting cubic feet, cubic yards, and cubic metres

Imperial measurements are entered in feet, and volume is shown in cubic yards. One cubic yard equals 27 cubic feet. Metric measurements are entered in metres, and volume is shown in cubic metres. One cubic metre is about 1.308 cubic yards. The tool also shows an approximate cubic metre equivalent so you can compare estimates across unit systems.

Keep dimensions in the selected system. Do not enter inches in a field labelled feet or centimetres in a metre field. If you switch units, the calculator converts the displayed dimensions, truck capacity, and cost rate to preserve the same physical estimate. Always check the labels again after changing units.

Common excavation estimating mistakes

A common error is using only the foundation footprint while forgetting depth or working room. Another is treating the top width of a sloped trench as its bottom width. Measure the actual planned cut and record which width is which. For several sections, make separate estimates where the dimensions change instead of averaging very different trenches together.

It is also easy to confuse bank volume with loose volume, or apply swell twice. Bank volume is the in-place cut; loose volume includes swell. Overdig is a separate allowance for extra excavation. Read estimates carefully to see which quantity a contractor or disposal site is using. Also check whether truck capacity is stated in cubic yards, cubic metres, or tons.

Finally, a volume estimate does not confirm that soil can be piled near the excavation or that a truck can reach it. Site access, utilities, groundwater, property lines, and spoil placement all affect the work. Review the job plan before excavation begins.

Safety, utilities, and site conditions

Before digging, identify underground utilities and follow the local utility-locating process. Private lines may not be included in public locating services. Check plans and have private services located where needed. A volume estimate does not show where cables, pipes, drains, or foundations are buried.

Excavation hazards include cave-ins, falling loads, water, hazardous atmospheres, nearby traffic, and equipment movement. Soil can fail without warning. Follow local rules for protective systems, access, spoil setbacks, inspections, and competent-person oversight. Never enter an unsupported trench based on a volume estimate or visual judgment alone.

For deep excavations, unstable ground, groundwater, or work near structures, involve qualified professionals. Keep people and equipment away from edges as required by the site plan. Safe excavation methods depend on the actual ground and conditions, not just the trench dimensions.

Limits of this excavation estimate

The calculator estimates geometric volume from the dimensions, count, working space, overdig, and swell values entered. It assumes consistent dimensions and soil conditions. It does not design slopes, shoring, foundations, drainage, dewatering, structural support, or legal truck payloads. The diagram is a simplified visual aid rather than an engineering or safety drawing.

For construction quantities, compare the result with drawings, field measurements, and contractor methods. For safety and structural decisions, use qualified engineering and excavation guidance. The final amount of soil removed and hauled can differ from the calculator due to actual conditions and site practices.

Excavation planning checklist

Before booking equipment, verify excavation length, width, depth, count, working room, top and bottom trench widths, and whether overdig is allowed. Confirm soil type and the swell factor. Check the truck capacity unit, legal payload, access route, loading point, and disposal or stockpile location.

Locate underground services and review the foundation or trench drawings. Confirm site protection, water management, and safe access with the responsible team. Keep the dimensions and assumptions with the quote so everyone understands whether a quantity refers to bank soil, loose soil, or trucked material. Revisiting these details can prevent costly differences between an early estimate and the final haul.