About the Excavation Calculator
Every foundation, basement, pond, pool, driveway and drainage trench starts with a hole, and every hole produces a pile of spoil that has to go somewhere. The volume of the hole is simple geometry. The volume of the pile is not the same number: soil that has been dug up breaks into lumps with air between them and takes up noticeably more space than it did in the ground.
This excavation calculator gives both. It works out the in-ground (bank) volume from the size and depth of the dig, applies a typical swell factor for the soil type to give the loose volume you will actually haul, and turns that into the number of truckloads or skips. It also estimates the weight, because a truck can reach its weight limit before it is full, and an optional removal cost.
How to Use the Excavation Calculator
Choose feet or metres. Unlike the landscaping calculators, the depth here is in feet or metres, because excavations are measured that way.
Pick the shape: a rectangle for most foundations and trenches, or a circle for a round pond or pit.
Enter the length and width, or the diameter, and the depth.
Choose the soil type. Sand, loam, clay and rock swell by very different amounts.
Enter the capacity of one truck or skip in cubic yards or cubic metres.
Optionally, enter the price per load for hauling or skip hire.
How Excavation Volume Is Worked Out
bank volume = length × width × depth (or π × d² ÷ 4 × depth)
loose volume = bank volume × (1 + swell %)
loads = loose volume ÷ capacity, rounded up
weight = bank volume × in-ground densityThe weight uses the bank volume and the in-ground density. Digging adds air, not mass, so the weight does not change when the soil swells.
Step-by-Step Example
A basement dig 20 by 15 feet and 3 feet deep in clay, 10 yd³ trucks at 300 a load.
Bank volume: 20 × 15 × 3 = 900 ft³ = 33.33 yd³
Swell: 33.33 × 1.35 = 45.00 yd³ loose
Loads: 45.00 ÷ 10 = 4.5 → 5 loads
Weight: 25.49 m³ × 1.9 t/m³ = 48.4 t ≈ 53.4 US tons
Cost: 5 × 300 = 1,500.00In metric, a hole 6 by 4 metres and 1 metre deep in loam is 24 m³ in the ground and 30 m³ loose, which fills five 6 m³ skips.
Typical Swell Factors
| Soil | Swell | In-ground density |
|---|---|---|
| Sand or gravel | about 12% | about 1.7 t/m³ |
| Loam or topsoil | about 25% | about 1.6 t/m³ |
| Clay | about 35% | about 1.9 t/m³ |
| Broken rock | about 60% | about 2.5 t/m³ |
These are typical planning figures. Wet soil is heavier, stony soil swells more, and the actual numbers on your site can differ, so treat the result as an estimate and allow some margin when booking trucks.
Volume Limits and Weight Limits
A dump truck or skip has two limits: how much it holds and how much it is allowed to carry. With light, fluffy soil the volume runs out first. With wet clay or rock, a truck can hit its legal weight limit while it still looks half empty.
That is why the calculator shows the weight each load would carry. Check it against the limit your haulier or skip company gives you. If it is too high, you need more, smaller loads, and the cost goes up accordingly.
Planning a Dig Safely
Locate buried services before any digging: gas, water, electricity and telecoms cables can all be close to the surface.
Support deep trenches. Trenches deeper than about 4 feet, or 1.2 metres, generally need shoring, a trench box or sloped (battered) sides to stop them collapsing. Sloping the sides increases the volume, so add it to your figures.
Plan where the spoil goes. Keep piles well back from the edge of the excavation, and decide early whether any topsoil will be kept for landscaping.
Follow local rules and get professional advice for anything deep, close to a building or near a boundary.
Keeping Topsoil Separate
On many sites the top few inches of soil are worth keeping. Topsoil is expensive to buy back, and it is the layer plants need.
Strip it first. Scrape off the topsoil across the whole area and stockpile it separately before digging deeper.
Measure it as its own layer. Run the calculator once for the topsoil depth and once for the subsoil below, so you know how much will stay on site and how much has to go.
Keep the heap small and loose. Large, compacted heaps of topsoil lose their structure. Keep them no higher than about 6 feet, or 2 metres, and away from traffic.
Understanding Your Result
Volume to dig out is the bank volume, the size of the hole.
Loose volume is what the spoil will occupy once dug, after swell.
Loads is the number of trucks or skips, with the weight each would carry.
Weight is the total weight of material removed.
Area and depth confirms the dimensions used.
Cost multiplies the loads by your price per load.
Worth knowing reminds you about weight limits and trench support.
When Should You Use This Calculator?
Pricing a foundation or basement dig.
Booking skips or trucks for spoil removal.
Digging a pond or pool.
Trenching for drainage or services.
Comparing quotes from excavation contractors.
Common Mistakes
Ordering trucks for the bank volume. The loose volume is 12–60% bigger.
Ignoring weight. Wet clay and rock can overload a truck that looks half full.
Forgetting sloped sides. Battered trench walls add to the volume dug.
Using one swell factor for everything. Rock swells about five times as much as sand.
Not checking for services before breaking ground.