How to use this calculator
- Enter or choose units.
- Enter or choose bottom length.
- Enter or choose bottom width.
- Enter or choose depth.
- Enter or choose side slope (horizontal per 1 vertical).
- The bank (in-place) volume updates as you type. Use Copy result or Share to keep it.
Method
V = D ÷ 6 × (A_bottom + 4 A_middle + A_top); A at depth z uses (L + 2s·z)(W + 2s·z); Loose = V × (1 + Swell)
- L, W
- bottom length and width
- D
- depth
- s
- side slope, horizontal per 1 vertical
Worked example
- Bottom 10 × 5 = 50 m²; top (10 + 2) × (5 + 2) = 84 m²; middle 11 × 6 = 66 m².
- V = 2 ÷ 6 × (50 + 4 × 66 + 84) = 132.667 m³.
- Loose = 132.667 × 1.25 = 165.833 m³ ÷ 10 m³ = 16.6 → 17 truckloads.
A 10 × 5 m pit 2 m deep with 0.5:1 sides holds 132.7 m³ in the ground, about 166 m³ loose, or 17 ten-cubic-metre loads.
What the result means
Price digging on the bank volume and haulage on the loose volume. If the soil goes back as compacted fill, it shrinks below its bank volume.
Assumptions and limits
- Level ground and a flat, rectangular bottom.
- All four sides have the same slope.
- Swell factors vary widely with soil and moisture; a site investigation gives better values.
- Does not assess trench stability or shoring.
Questions
What is the difference between bank and loose volume?
Bank volume is soil as it sits in the ground; once dug it loosens and takes up more space, by the swell percentage.
Is the prismoidal formula exact here?
Yes. For a pit with straight, evenly sloped sides the cross-section area is a quadratic in depth, which the prismoidal formula integrates exactly.
Please note: Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials.