Your excavation and spoil quantity
Does your result look realistic?
What affects the result most?
What to do with the result
Continue your groundworks and foundation estimate
Use the excavation dimensions to estimate fill, concrete, reinforcement or a paved surface.
How to calculate excavation volume for a trench or foundation pit
This excavation calculator starts with length, width and depth. With straight sides, the in-situ or bank volume is simply the bottom excavation area multiplied by depth. This works for trenches, strip excavations and rectangular pits when the sides can be represented as vertical in the quantity takeoff.
If the dimensions you know describe a structure rather than the actual excavation, enter the required working space per side. Numbivo adds it to both ends of the length and both sides of the width before calculating the excavation.
Trench excavation calculator in m³ or cubic yards
For a trench, enter the trench length, excavation width and depth. Set working space to zero when the width already includes the full excavation. Switch units to get the same calculation in feet and cubic yards.
This answers common planning questions such as how many cubic yards of dirt will I excavate or how many cubic metres of trench spoil must be handled.
Sloped foundation excavation and side-slope volume
For a sloped pit, enter the slope as horizontal run per 1 vertical rise or as an angle from horizontal. Numbivo calculates the larger top dimensions and uses the prismoidal formula for a rectangular excavation whose length and width change linearly with depth.
This is geometry only. The calculator does not determine whether a slope is safe for a particular soil or site.
Where to get the input data
The quality of an excavation estimate depends more on the inputs than on the arithmetic. Use the drawing, site measurement or project specification for the excavation dimensions rather than guessing from the finished structure.
Geometry and working space
Take length, width and depth from the excavation drawing, setting-out dimensions or a measured trench. Get working space and any required side-slope geometry from the project method, temporary-works information or other site-specific requirements.
Density and bulking
Use geotechnical information, a soil report, a disposal facility, a haulier or a project estimate when available. Do not assume one density or bulking percentage represents every soil, moisture condition or rock content.
Truck capacity and payload
Use the actual body volume and allowable project or vehicle payload for the truck, skip, container or trailer you expect to use. Capacity by volume and capacity by mass are different limits.
Excavation and disposal prices
Enter the basis used in your quote: digging per bank volume, haulage per load and disposal per tonne or short ton. Leave a rate at zero when that cost is outside your estimate.
Excavated soil volume, swell factor and bulking factor
Soil commonly occupies more volume after excavation because its original structure is disturbed. Contractors may describe this as swell, bulking or loose volume. The calculator keeps the in-situ excavation volume separate from the loose spoil volume so truck and stockpile planning is not based on the smaller bank volume.
A 25% increase corresponds to a bulking factor of 1.25. The correct factor is project-specific, so the input is editable rather than tied to one soil type. If the result looks unexpectedly large, first check whether your source gives a percentage increase or a multiplication factor; entering 1.25 as 125% would not mean the same thing as a factor of 1.25.
Excavated soil weight and truck-load calculator
Estimated mass is based on the in-situ density you enter. Truck trips are rounded up from the loose spoil volume. If a payload limit is entered, Numbivo also calculates trips by weight and uses the larger result.
This is useful because a truck may reach either its body volume or its payload limit first. The dynamic interpretation tells you which limit controls the current estimate.
Excavation cost, muck-away and disposal estimate
The optional cost section combines a price per in-situ volume for digging, a price per truck load for haulage and a disposal price per tonne or short ton. Leave any item at zero if it is not part of your estimate.
The result does not automatically include mobilisation, dewatering, shoring, permits, contaminated soil, tipping surcharges, machine standby time or reinstatement.
Does your excavation result look realistic?
Start with a geometry check. For vertical sides, multiplying the displayed bottom length × bottom width × depth should reproduce the in-situ volume. For sloped sides, the top dimensions must be larger than or equal to the bottom dimensions. If they expand much more than expected, recheck the slope convention and depth.
Then compare the loose-spoil result with the bank volume. The difference should be exactly the bulking increase you entered. Finally, compare truck loads by volume with loads by payload. A large difference is not automatically an error, but it is a reason to verify soil density, loose-volume assumptions and the actual truck specification.
What affects the result most?
Length, width and depth control the base excavation volume. Working space increases both plan dimensions, so even a modest allowance can add substantial volume to a large pit. With sloped sides, deeper excavations also create more horizontal run and a larger top footprint.
Bulking changes loose spoil and truck planning without changing the bank volume. Density changes estimated mass and can increase payload-limited trips. Truck capacity changes trip count but does not change the amount of soil.
What to do with the result
Use bank volume for excavation quantity where the rate is based on in-situ material. Use loose volume for spoil stockpiles and volume-limited haulage. Use estimated mass for payload and weight-based disposal planning.
Before ordering haulage, test a second scenario with the realistic low/high values from your project information. If the excavation will be backfilled or will receive concrete, continue with the linked aggregate and concrete calculators rather than reusing the excavation volume as if every layer occupied the same space.
For construction students and apprentices: excavation volume mini-lesson
An excavation estimate separates three quantities that are easy to confuse: bank volume is the volume before digging, loose volume is the disturbed spoil after bulking, and mass is the estimated weight of the excavated material. They use different units and answer different planning questions.
Unit check: m × m × m gives m³. Multiplying m³ by kg/m³ leaves kg. Truck trips are whole numbers, so a partial final load is rounded up when planning the number of trips.
Quick worked example: a 10 m × 1 m × 1.5 m vertical trench has 15 m³ bank volume. With 20% bulking, loose spoil is 18 m³. An 8 m³ truck therefore needs 18 ÷ 8 = 2.25, rounded up to 3 volume-limited trips before any payload check.
Practice exercises
Load each exercise into the real calculator, solve it by hand and reveal the worked result.
Exercise 1: service trench
20 m long, 0.6 m wide and 1.2 m deep. Vertical sides, 25% bulking, 1,700 kg/m³ soil, 8 m³ truck and 12 t payload.
Exercise 2: sloped foundation pit
8 × 6 m structure, 2 m deep, 0.5 m working space, 0.5H:1V side slope, 30% bulking, 1,800 kg/m³ soil.
Exercise 3: trench in US units
50 × 2 × 4 ft trench, vertical sides, 20% bulking, 105 lb/ft³ soil, 10 yd³ truck and 12 short-ton payload.
Before excavation starts
This tool estimates quantities, not excavation safety. It does not locate underground utilities, classify soil, design shoring, choose a safe slope, check groundwater, assess adjacent foundations or verify local excavation requirements.
Use the project and site requirements for excavation geometry and protection. For a connected foundation workflow, see the foundation excavation, concrete and rebar planning guide. If the excavation will receive imported stone or concrete, continue with the Gravel & Aggregate Calculator or Concrete Calculator.
Learn the estimating method
Go deeper into the method or check reference values without losing the context of this calculation.