Soil Excavation Calculator
Enter the pit length, width, depth and slope ratio to calculate the in-situ excavation volume, the loose (swollen) volume and the backfill required — useful for site excavation, muck-away and refill estimating.
Input Data
Results
At a glance:Pit excavation uses the truncated-pyramid (frustum) formula: top dimensions = base dimensions + 2 × slope × depth. Volume V = depth/3 × (base length × base width + top length × top width + √(base area × top area)). Loose (dug) volume = V × swell factor; backfill loose soil = V × backfill% × swell. With slope 0 the shape is a rectangular prism and the formula reduces to length × width × depth.
Formula
Top length = base length + 2 × slope × depth
Top width = base width + 2 × slope × depth
V = depth/3 × (base area + top area + √(base area × top area))
Loose volume = V × swell
Backfill loose = V × backfill% × swell
$$L_t = L + 2 s h,\quad W_t = W + 2 s h$$$$V = \frac{h}{3}\left(LW + L_t W_t + \sqrt{LW\cdot L_t W_t}\right)$$$$V_{\text{loose}} = V\,k$$$$V_{\text{back}} = V\,p\,k$$How to Use
- Enter the pit base length, base width and excavation depth.
- Set the slope ratio (0 for vertical walls).
- Enter the swell factor (usually 1.2–1.3) and backfill ratio.
- The tool outputs the in-situ, loose and backfill volumes.
Case Studies
Vertical-wall foundation pit
5×3 m, depth 2 m, slope 0, swell 1.25.
In-situ 30 m³; loose 37.5 m³; backfill 90% = 33.75 m³ loose.
Sloped stable pit
4×4 m, depth 3 m, slope 0.5, swell 1.3.
Top 7×7 m; in-situ about 99.3 m³; loose about 129 m³.
FAQ
What is the swell factor?
When soil is dug it gains pores and expands; the swell factor is that expansion multiplier. Ordinary soil is about 1.2–1.3, and trucks and stockpiles are measured loose.
What is the slope ratio?
The horizontal distance the wall moves out per 1 m of depth. 0 is a vertical wall; 0.5:1 is common for soil stability, larger for soft soil.
Why is backfill less than the dug volume?
Part of the pit is often backfilled and the rest removed; compacted backfill also takes less volume than the loose dug soil. Set the backfill ratio to actual need.
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References
Content review: Calculatorism Construction Team. Results are for reference only; please refer to the relevant authorities for the official figures.