Excavation Dirt Removal (Volume Formula)

Measure the excavation in place, then convert that volume to the larger loose volume that must be hauled. For a rectangle, multiply length by width by average depth, then divide by 27 to get bank cubic yards. Apply a project-specific soil swell factor, and check every truck load against both usable space and legal payload.

Accurate dirt-removal estimates save more than disposal fees. They help you schedule the right truck size, avoid extra trips, and reduce time spent idling while equipment waits for a haul. They also give you a practical way to compare the excavation estimate with truck counts or disposal records.

I plan an estimate in three stages: measure the soil before digging, account for how it expands when disturbed, and check how much each truck can legally carry. The result is a working estimate, not a substitute for checking actual excavation dimensions and material as the job proceeds.

For a rectangular excavation, use:

Bank volume (BCY) = length (ft) × width (ft) × average depth (ft) ÷ 27

BCY means bank cubic yards. The division by 27 converts cubic feet to cubic yards, since one cubic yard contains 27 cubic feet.

Measure length and width in feet, and use the average depth in feet. For example, a trench that is 60 feet long, 3 feet wide, and 4 feet deep has a bank volume of:

60 × 3 × 4 ÷ 27 = 26.7 BCY

This formula assumes the excavation is rectangular and has a consistent footprint. If the sides slope, the bottom changes width, or the depth varies, a single length, width, and depth can misstate the amount of soil. Measure the actual shape in sections instead.

Measuring average depth

Average depth is the mean of several depth readings across the excavation, not simply the deepest point. Take readings at regular points along the length and across the width, especially where grade or ground level changes.

For example, if four measured depths are 2, 3, 3, and 4 feet, the average is 3 feet. Use more readings where the ground is uneven or the excavation changes shape. Record measurements and units as you go so you can check the estimate later.

Calculating irregular excavations and loose haul volume

For an irregular excavation, split the area into smaller, measurable shapes or take cross-sections at known intervals. Calculate each section, then add the results. If cross-sections have different areas, the average end-area method estimates the volume between them.

Use V = [(A₁ + A₂) ÷ 2] × distance, where A₁ and A₂ are the cross-sectional areas at each end, and distance is the spacing between them. Keep units consistent. If areas are in square feet and distance is in feet, the result is cubic feet; divide by 27 for cubic yards.

Once you have bank volume, estimate the loose volume using a swell factor. Swell describes how much a material’s volume increases after excavation. It varies with soil or rock type, moisture, and handling, so use a project or geotechnical value when available rather than assuming one factor fits every site.

Loose volume (LCY) = bank volume (BCY) × (1 + swell factor)

LCY means loose cubic yards. Enter the swell factor as a decimal: for a project value of 20%, use 0.20. If the excavation is 26.7 BCY, the estimate becomes 26.7 × 1.20 = 32.0 LCY. This is an example of the calculation, not a recommended swell value.

For metric measurements, calculate cubic metres directly:

Volume (m³) = length (m) × width (m) × average depth (m)

One cubic metre equals about 1.30795 cubic yards. Keep bank and loose quantities labeled separately when converting or sharing estimates.

Estimate truck loads by space and weight

Truck-load estimates require two checks. First, divide loose volume by the truck’s usable volume capacity. Second, confirm that the material’s weight will remain within the vehicle’s legal payload. The lower practical limit may be set by space or weight.

Loads = round up (LCY ÷ usable truck volume capacity)

Use usable capacity, not just the truck’s advertised or nominal cubic-yard figure. The amount that can be loaded may depend on the truck body, material, moisture, and safe loading practice. Ask the hauler what capacity applies to your soil and route.

These are worked examples using an assumed swell factor and stated usable truck space. They do not establish the right swell factor, truck capacity, or legal payload for a real job. A volume-based load count can be too high if weight limits are reached first.

To check payload, get a suitable material density from the project information or a qualified supplier, then compare the estimated load weight with the truck’s legal payload. Moisture can change soil weight. Do not assume that a truck filled to its volume limit is within its weight limit.

Plan the work, equipment, and safety controls

Before digging, confirm the excavation limits, finished grades, access route, soil conditions, and spoil destination. Have underground utilities located and marked through the applicable utility-locate service before excavation begins. Visual checks or old plans alone do not reliably identify buried services.

Match the excavator and truck to the soil, access, and haul distance. A larger bucket may move material quickly, but it must suit the machine and working conditions. Confirm the excavator’s rated lift at the working radius, and check truck payload as well as volume. The rating at the actual reach matters; do not rely only on the machine’s largest published lift figure.

Set a clear truck loading zone and keep people out of the machine’s swing radius. Excavate in controlled lifts suited to the soil and equipment, and keep checking actual depth and footprint. If the soil, groundwater, or excavation shape differs from the plan, pause and reassess the method and volume.

Excavation walls can collapse, and utility strikes can cause electrocution, flooding, or explosion. Use access controls and protective systems that fit the depth, soil, and applicable rules. Keep personnel out of unsupported hazardous excavations. When conditions are uncertain, get qualified site-safety advice before work continues.

Worked site examples

These examples show how the math changes with the shape and truck plan. They are illustrative calculations, not records from specific jobs. In each case, use measured dimensions and a project-supported swell factor for an actual estimate.

Rectangular pad: A 30-by-20-foot area excavated to an average depth of 2 feet contains 30 × 20 × 2 ÷ 27 = 44.4 BCY. With an assumed 20% swell factor for demonstration, loose volume is 44.4 × 1.20 = 53.3 LCY. At 10 cubic yards of usable space per load, the volume estimate rounds up to six loads, subject to payload.

Changing cross-sections: Suppose a trench section has an area of 12 square feet at one end and 18 square feet at the other, over 20 feet. Its estimated volume is [(12 + 18) ÷ 2] × 20 = 300 cubic feet, or 11.1 BCY after dividing by 27. Repeat for each interval and add the results before applying swell.

Truck planning: If the loose estimate is 53.3 LCY and the hauler confirms 9 usable cubic yards per load, the volume-based count is round up (53.3 ÷ 9) = 6 loads. Verify weight separately. If payload limits prevent carrying 9 cubic yards of that material, use the lower load size when scheduling.

Check quantities and close out the site

Recheck the footprint and depth as work advances. Compare the estimate with truck counts, scale tickets, or disposal records. If the difference is large, review the measured dimensions, assumed swell, actual soil, truck capacity, and whether material was left on site or mixed with other loads.

A simple field record can include:

• Excavation length, width, and depth readings
• Calculated bank volume and the method used
• The swell value and its source
• Loose-volume estimate and confirmed truck capacity
• Truck counts, scale tickets, or disposal receipts

At the end, verify final dimensions and grade, secure or restore the work area, and remove spoil from access routes. Clean and inspect equipment according to the manufacturer’s instructions. Keeping the measured quantity and haul records together makes the next estimate easier to check.

Frequently asked questions

How do I calculate dirt removal for a rectangular excavation?
Multiply length by width by average depth, all in feet, then divide by 27 to get bank cubic yards. Convert bank volume to loose volume with a project-specific swell factor before estimating truck space.

How do I calculate average excavation depth?
Take depth readings at several points, add them, and divide by the number of readings. Use more points where the ground or excavation depth varies, and record the measurements used.

What swell factor should I use for excavated soil?
Use a value supplied for the project or supported by geotechnical information. Swell varies with material and moisture, so there is no single factor that applies to every excavation.

How many truckloads will I need?
Divide estimated loose cubic yards by confirmed usable truck capacity and round up. Then check payload separately, since material weight may limit a load before the truck body is full.

Can I use the deepest point as the average depth?
No. The deepest point alone can overstate the average for a sloped or uneven excavation. Take multiple measurements across the area and use their mean, or calculate sections separately.

How do I estimate an irregular excavation?
Divide it into smaller measured shapes and add their volumes, or use cross-sections and the average end-area formula. Keep units consistent and convert cubic feet to cubic yards by dividing by 27.

Should utility locating happen before excavation?
Yes. Have underground utilities located and marked through the applicable service before digging. Do not rely on visual assumptions or estimates to identify buried services.

Why might truck counts differ from my estimate?
Differences can come from inaccurate dimensions, a swell assumption that does not fit the soil, varying moisture, truck capacity, weight limits, or soil left on site. Compare measurements with tickets and revise the estimate.

Does the truck’s listed cubic-yard capacity guarantee that it can haul that much soil?
No. Listed capacity may not equal usable capacity for a specific material, and legal payload can limit the load. Confirm both with the hauler before scheduling.

(This article was written by one of our staff writers, Victor Dempsey. Visit our Meet the Team page.)