What is the difference between bank volume and loose volume?

Bank volume (also called in-situ volume) is the volume of soil in its natural, undisturbed state — the volume of the hole you are digging. Loose volume is the volume that same soil occupies after it has been excavated. When soil is dug out, it is broken up, aerated, and expanded — this is called swell. Swell by soil type: • Topsoil / loam: +25% (1 m³ in ground = 1.25 m³ loose) • Clay: +30% • Sand / gravel: +12% • Soft rock / shale: +35% • Hard rock: +40% Why it matters: when ordering trucks to remove spoil, you need to use the loose volume, not the bank volume. Ordering 10 truck loads based on bank volume for clay will leave you 3 loads short.

How do I calculate excavation volume for a rectangular pit?

Volume = Length × Width × Depth Example — house foundation 8m × 6m × 1.2m deep: Volume = 8 × 6 × 1.2 = 57.6 m³ In cubic yards: 57.6 × 1.308 = 75.3 yd³ With 25% swell (topsoil): Loose volume = 57.6 × 1.25 = 72 m³ At 10 m³ per truck: 72 / 10 = 7.2 → 8 truck loads Note: for sites with multiple areas to excavate (e.g. strip foundations), calculate each section separately and add the volumes together.

What is a batter ratio for sloped excavations?

A batter (or slope ratio) describes how far a trench or pit wall is cut back for every unit of depth. Batter ratio = horizontal run : vertical depth Examples: • 0.5:1 — wall steps out 0.5m for every 1m of depth • 1:1 — wall steps out 1m for every 1m of depth (45°) • 1.5:1 — gentler slope for loose sandy soils Why batters are used: 1. Safety: vertical trench walls can collapse, especially in sandy soil. Health and safety regulations often require sloped walls beyond a certain depth. 2. Rock cuts: rock cuts are typically vertical; clay and sand require significant batters. Typical batter requirements: • Rock: 0:1 (vertical) • Stiff clay: 0.25:1 to 0.5:1 • Clay: 0.5:1 to 1:1 • Sand: 1:1 to 1.5:1 • Loose fill: 1.5:1 to 2:1

How many truck loads do I need for my excavation?

Truck loads = Loose volume / Truck capacity Always use loose volume (not bank volume) — excavated soil is bulkier. Truck capacities: • Small tipper / skip lorry: 4–6 m³ • Standard dump truck: 8–10 m³ • Large articulated dump truck: 14–20 m³ Example — 18 m³ bank volume, topsoil (25% swell), 10 m³ trucks: • Loose volume: 18 × 1.25 = 22.5 m³ • Loads: 22.5 / 10 = 2.25 → 3 loads (always round up) Practical note: in practice, trucks rarely fill to exact capacity due to the nature of loose soil. Add 10% to your calculated load count as a buffer.

How much does excavation cost?

Excavation cost depends heavily on soil type, depth, site access, and location. Rough guides: Machine excavation: • Soft topsoil / loam: $15–$40 per m³ • Clay: $25–$60 per m³ • Hard clay / soft rock: $50–$120 per m³ • Rock (blasting required): $100–$300+ per m³ Spoil removal (tipping/disposal): • Clean topsoil (reusable): $0–$10 per m³ • Mixed soil: $10–$25 per m³ • Contaminated soil: $50–$200+ per m³ (regulated disposal) Typical project costs: • Small house foundation (50 m³): $2,000–$5,000 • Swimming pool excavation (80 m³): $3,000–$8,000 • Trench for services (per metre run): $30–$80 Always get 3 quotes from licensed excavation contractors. Costs vary enormously by region.

What is the prismatoid formula and when is it used?

The prismatoid formula gives the exact volume of any shape with a flat top and bottom (like a sloped-wall excavation): V = (D / 6) × (A_bottom + 4×A_middle + A_top) Where: • D = depth • A_bottom = area of bottom face • A_top = area of top face (wider, due to batter) • A_middle = area at mid-depth For a rectangular excavation with sloped walls: • Top width = base width + 2 × batter × depth • Top length = base length + 2 × batter × depth The prismatoid formula is more accurate than the simple frustum formula or just taking the average of top and bottom areas. For shallow excavations with gentle batters the difference is small, but for deep excavations with steep batters it becomes significant.

Excavation Volume Calculator — m³, Truck Loads & Cost

The Excavation Volume Calculator computes the volume of any excavation in cubic metres, cubic yards, and cubic feet. Choose from four shapes: Rectangle (foundations, ponds), Circle (tanks, soakaways), Trench (pipes and drainage), or Sloped Walls (using the exact prismatoid formula for battered excavations). Select your..

DIMENSIONS

LENGTH (m)

WIDTH (m)

DEPTH (m)

SOIL TYPE

Topsoil / Loam: 1280 kg/m³ · +25% swell

TRUCK CAPACITY (m³)

COST PER m³ (optional)

RESULTS — RECTANGLE · Topsoil / Loam

BANK VOLUME (IN-SITU)

18.000 m³

= 23.54 yd³ · 635.7 ft³

LOOSE VOLUME

22.50 m³

+25% swell

SOIL WEIGHT

23.0 t

tonnes

TRUCK LOADS (10 m³ each)

3 loads

RECTANGULAR EXCAVATION

EXCAVATION SUMMARY

Bank volume18.000 m³

Loose volume (+25% swell)22.50 m³

Soil weight23.04 tonnes

Truck loads (10 m³/truck)3

SOIL REFERENCE

SoilDensitySwell

Topsoil / Loam1280 kg/m³+25%

Clay1500 kg/m³+30%

Sand / Gravel1700 kg/m³+12%

Mixed Soil1400 kg/m³+20%

Soft Rock / Shale2200 kg/m³+35%

Hard Rock2600 kg/m³+40%

VOLUME CONVERSIONS

1 m³1.308 yd³ = 35.31 ft³

1 yd³0.765 m³

1 ft³0.0283 m³

Created with❤️byeaglecalculator.com

HOW TO USE

1
Select your excavation shape: Rectangle (house foundation, pond, flat-bottomed pit), Circle (circular tank, soakaway, round pond), Trench (pipes, cables, drainage — same formula as rectangle but emphasises length), or Sloped Walls (excavations where sides are cut at an angle for safety or soil stability).
2
Enter your dimensions in metres or feet. For Rectangle and Trench enter length, width, and depth. For Circle enter diameter and depth. For Sloped Walls enter the base (bottom) length and width, depth, and batter ratio. The batter ratio is how many horizontal units for every 1 vertical unit — 0.5:1 means the wall steps out 0.5m for every 1m of depth.
3
Select your soil type — this affects both the density (for weight calculation) and the swell factor (how much the excavated soil expands once removed). Clay swells up to 30%, loose sand/gravel only 12%. The soil reference table on the right shows all values.
4
Enter your truck capacity in m³ (standard dump trucks range from 6–14 m³) and optionally enter your cost per m³ to get a total excavation cost estimate. Note: the cost is applied to the bank (in-situ) volume, which is how excavation contractors typically quote.
5
Read your results: bank volume in m³, yd³, and ft³; loose (excavated) volume accounting for swell; soil weight in tonnes; and number of truck loads needed to remove the spoil. The isometric cross-section diagram updates live as you change shape and dimensions.

WORKED EXAMPLE

Excavation for a basement extension: 8m × 5m base, 2.5m deep, clay soil, 0.5:1 batter Step 1: Calculate top dimensions (batter adds width on both sides) Top length = 8 + 2 × 0.5 × 2.5 = 8 + 2.5 = 10.5 m Top width = 5 + 2 × 0.5 × 2.5 = 5 + 2.5 = 7.5 m Step 2: Prismatoid formula A_bottom = 8 × 5 = 40 m² A_top = 10.5 × 7.5 = 78.75 m² A_mid = ((8+10.5)/2) × ((5+7.5)/2) = 9.25 × 6.25 = 57.8125 m² Volume = (2.5/6) × (40 + 4×57.8125 + 78.75) = 0.4167 × (40 + 231.25 + 78.75) = 0.4167 × 350 = 145.83 m³ Compare: simple rectangle (8×5×2.5) = 100 m³ — battered walls add 46% more spoil! Step 3: Loose volume (clay +30% swell) 145.83 × 1.30 = 189.6 m³ Step 4: Soil weight 145.83 × 1500 kg/m³ = 218,745 kg = 218.7 tonnes Step 5: Truck loads (10 m³ each) 189.6 / 10 = 18.96 → 19 truck loads Step 6: Cost at $40/m³ 145.83 × $40 = $5,833

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Last updated: April 29, 2026 · Formula verified by EagleCalculator team · Eagle-eyed accuracy for every calculation.