TryBuildCalcPit Excavation Calculator (Sloped Earthwork Volume, Truck Loads & Cost)
Calculate sloped pit excavation volume, loose soil, trucks, and cost.
Calculate sloped pit excavation volume using bottom and top dimensions, depth, swell factor, truck loads, and cost. Adjust top size, bottom size, depth, units, swell factor, trucks, and cost to match your site.
🕒 Last updated: July 30, 2026
Inputs
ℹ️Typical: 10–40% (Sand ~15%, Clay ~30%, Rock ~60%)
ℹ️Used only to convert volume into an approximate weight in tons — does not affect volume, swell, or cost.
You need approximately 48.779 m³ (~78.05 t) of pit excavation.
Based on frustum (sloped pit) calculation
Calculations
Pit Volume: 40.649 m³ (~65.04 t)
Loose Volume: 48.779 m³ (~78.05 t)
Swell Added: +8.13 m³ (~13.01 t)
Approximate results for planning only. Verify with a professional.
Looking for the verification checklist, reference tables, or tips and mistakes?See the complete Pit Excavation Calculator.
Pit excavation volume estimate
This page is pre-filled for a practical sloped pit with a 4 m x 3 m bottom (12 m²) and a larger 6 m x 5 m top (30 m²) over a 2 m depth — the frustum formula gives 40.65 m³ of bank volume, becoming 48.78 m³ after 20% swell.
At a 5 m³ truck capacity, that's 10 truck loads, costing an estimated 14,634 at the sample rate of 300 per m³ applied to the loose volume.
- Bottom: 4 m x 3 m. Top: 6 m x 5 m.
- Bank volume: 40.65 m³.
- Loose volume: 48.78 m³, 10 truck loads.
How does pit excavation volume calculation work?
Pit excavation is calculated using the frustum formula, which accounts for different top and bottom areas due to slope.
Step 1 — Calculate Excavation Volume (Frustum Method)
If using the batter/slope helper: Top Length/Width = Bottom Length/Width + (2 × Depth × Batter Ratio)
Getting the top dimensions right is the hardest part of a pit estimate by hand — instead of guessing, turn on "Auto-Calculate Top Dimensions from Slope?" and enter either a batter ratio (horizontal run per 1 unit of depth) or a slope angle from horizontal. The calculator applies that offset to both sidesof the bottom footprint (hence the ×2) and fills in the top length and width for you, so a wrong-by-hand top dimension can't silently understate or overstate your volume.
Where:
- A₁ = Bottom area (Length × Width)
- A₂ = Top area (Length × Width)
- D = Depth of excavation
This formula gives a more accurate volume compared to rectangular calculation when slopes are present.
Step 2 — Apply Swell Factor
Excavated soil expands after removal due to loosening. This increase is called swell and depends on soil type:
- Sand / Gravel → ~10–20%
- Ordinary / Mixed Soil → ~20–30%
- Clay → ~20–40%
- Rock → ~50–80%
Step 3 — Calculate Truck Loads
If Truck Capacity is entered in cft: Truck Capacity (m³) = Truck Capacity (cft) ÷ 35.3147
This determines how many truck trips are required to transport excavated soil. Truck capacity can be entered in m³ or cft — a cft value is converted to its m³ equivalent first, then the same formula applies.
Step 4 — Estimate Excavation Cost
If Cost is entered per cft: Cost per m³ = Cost per cft × 35.3147
Cost varies depending on soil type, excavation method, labor, and machinery. The cost rate can be entered per m³ or per cft — a cft rate is converted to its m³-equivalent rate before multiplying, since 1 m³ = 35.3147 cft.
Step 5 — Add Contingency (Optional)
Total Cost = Base Cost + Contingency Amount
Pit work carries more unknowns than a simple vertical cut — groundwater, unexpected side instability, over-excavation to reach a stable batter, and restricted access all tend to push costs up mid-job. Contingency is an optional buffer on top of the base cost to cover exactly that. It defaults to 0%; a commonly used range is 5-15% depending on how well the ground conditions and access are already known.
Multiple Different-Sized Pits
If you have several pits of identical size, use the Number of Units multiplier. If your pits are different sizes— mixed footing pits, or stepped excavation stages — switch on "Multiple Different-Sized Pits?" and enter each size as its own section (up to 10). The calculator computes each section's frustum volume separately and sums them into one total before applying swell, truck loads, and cost.
Example pit excavation calculation
This example uses the active calculator inputs above and follows the same steps from the formula section — showing the default scenario if you haven't changed anything, or your own live inputs once you do.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Bottom | 4 m × 3 m | Sets the smaller area (A₁) at the base of the frustum |
| Top | 6.000 m × 5.000 m | Sets the larger area (A₂) at ground level |
| Depth | 2 m | Vertical distance between top and bottom areas |
| Number of units / Swell factor | 1, 20% | Multiplies volume for identical pits, then converts to loose (haulage) volume |
Step 1 — Calculate Volume (Frustum Method)
| Calculation | Substitution | Result |
|---|---|---|
| Bottom area (A₁) | 4 × 3 | 12.000 m² |
| Top area (A₂) | 6.000 × 5.000 | 30.000 m² |
| Volume per unit | (D ÷ 3) × (A₁ + A₂ + √(A₁ × A₂)) | 40.649 m³ |
| Total volume | 40.649 × 1 | 40.649 m³ |
Step 2 — Apply Swell Factor
| Calculation | Substitution | Result |
|---|---|---|
| Loose volume | 40.649 × (1 + 20/100) | 48.779 m³ |
Step 3 — Truck Loads & Cost
| Calculation | Substitution | Result |
|---|---|---|
| Enable cost estimation above to see truck loads and cost | — | |
Therefore, this pit excavation needs approximately 48.779 m³ of loose soil.
This page keeps things focused on the calculation above. For the full construction guide — verification checklist, reference tables, usage steps, tips, common mistakes, and limitations.See the complete Pit Excavation Calculator.