Patio excavation: bank volume, loose spoil and disposal
Excavation has two different volume questions: how much ground comes out, and how much space the excavated material occupies afterward. Disposal also introduces a separate weight question.
By PatioBoQ · Updated · Methodology & limits
Bank volume is the ground before excavation
For a uniform rectangular excavation, bank volume = area × excavation depth. Use consistent units. In US units, area in square feet × depth in feet gives cubic feet; divide by 27 for cubic yards.
Our default example assumes the finished patio surface stays at the existing ground level. The assumed excavation depth is therefore the sum of paver, bedding and compacted base thicknesses: 60 + 25 + 150 = 235 mm. This is a geometry assumption, not a prescribed dig depth.
If the finished level changes, the calculation changes. Existing pavement, topsoil, local low spots, base extension and unsuitable material also need separate treatment. A photograph alone cannot confirm these depths.
Worked example: a 20 × 14 ft patio
This is an estimating example, not a recommended construction design. It assumes 60 mm pavers, 25 mm bedding, 150 mm compacted base, 10% paver waste and a 1.25 spoil swell factor. Finished and existing ground levels are assumed equal.
| Quantity | US units | Metric units |
|---|---|---|
| Net patio area | 280.00 sq ft | 26.01 m² |
| Paver order, 10% allowance | 308.00 sq ft | 28.61 m² |
| Compacted base | 5.10 cu yd | 3.90 m³ |
| Bedding sand | 0.85 cu yd | 0.65 m³ |
| Bank excavation | 8.00 cu yd | 6.11 m³ |
| Loose spoil, 1.25× | 9.99 cu yd | 7.64 m³ |
Displayed quantities are rounded to two decimals. Confirm material specifications and delivery units with your supplier before ordering.
Loose spoil uses a stated swell factor
The example bank excavation is 6.113020032 m³. With an illustrative swell factor of 1.25, the loose spoil volume is 7.64127504 m³, about 9.99 cubic yards. The factor describes volume expansion after digging; it does not mean extra soil mass has been created.
Do not treat 1.25 as a measured property of your site. Ask the contractor which soil conditions and handling assumptions support the disposal allowance. If the material is wet, mixed with demolition debris or stored differently, a single factor may not describe the load well.
Why a “10-yard dumpster” is not automatically enough
A nominal container volume close to your loose spoil estimate does not establish that the load is acceptable. Ask the hauler about the permitted material, weight limit, loading height, access and any surcharge. Soil, concrete and mixed debris may have different handling requirements.
The calculator estimates volume; it does not choose a vehicle, approve a container loading plan or calculate a verified spoil weight. Those decisions require the hauler’s requirements and suitable site-specific material data.
Keep demolition and soil separate
Removing an existing slab is not the same task as digging an equivalent volume of soil. Clarify the existing surface, its thickness if known, breakout work, loading and disposal. If soil excavation is measured from the underside of a removed layer, avoid counting that layer a second time.
Quote wording such as “excavate for patio” leaves several questions open. It does not prove that disposal is excluded. Ask for the included depth, assumed material and number or allowance of loads in writing.
Use these three disposal questions
- Which existing materials and excavation depth are included in the price?
- Does the total include loading, transport, container rental and disposal charges?
- What happens if the actual quantity, weight or ground condition differs from the allowance?
For the broader scope, use the 16-item patio quote checklist. For how quantities are computed, see the methodology.