Earthwork Volume Calculator Formula
Understand the math behind the earthwork volume calculator. Each variable explained with a worked example.
Formulas Used
Bank (in-place) Volume
bank_volume = (area1 + area2) / 2 * distanceLoose (truck) Volume
loose_volume = (area1 + area2) / 2 * distance * (1 + swell_factor / 100)Variables
| Variable | Description | Default |
|---|---|---|
area1 | Cross-Section Area 1 (A1)(m^2) | 25 |
area2 | Cross-Section Area 2 (A2)(m^2) | 35 |
distance | Distance Between Sections(m) | 50 |
swell_factor | Swell Factor(%) | 25 |
How It Works
Average End Area Method
The average end area method estimates earthwork volume between two surveyed cross-sections.
Formula
V = (A1 + A2) / 2 x L
where A1 and A2 are the cross-sectional areas at each station and L is the distance between them. For excavated material, apply a swell factor (typically 20-40%) because soil expands when dug out. The loose volume is what determines truck loads.
Worked Example
Cross-sections of 25 m^2 and 35 m^2, 50 m apart, 25% swell.
- 01Bank volume = (25 + 35) / 2 x 50 = 30 x 50 = 1500 m^3
- 02Loose volume = 1500 x 1.25 = 1875 m^3
- 03Truck loads (10 m^3 per truck) = 1875 / 10 = 188 loads
Frequently Asked Questions
What is swell factor for common soils?
Sand: 10-15%. Ordinary earth/loam: 20-30%. Clay: 25-40%. Rock: 40-60%. Swell factor is the percentage increase in volume when material is excavated from its in-place (bank) state.
Is the average end area method accurate?
It slightly overestimates volume, especially when A1 and A2 differ greatly. The prismoidal correction can improve accuracy: V_prismoidal = L/6 (A1 + 4Am + A2), where Am is the area at the midpoint.
What is shrinkage in earthwork?
When soil is used as fill and compacted, it occupies less volume than in-place (bank) due to densification. Shrinkage factors: sandy soil 5-10%, clay 10-15%. Bank volume x (1 - shrinkage) = compacted fill volume.
Ready to run the numbers?
Open Earthwork Volume Calculator