1) Why duct bank sizing matters
Duct banks protect power and communications routes while keeping alignment predictable for pulling and maintenance. Small changes in spacing, cover, or layout can significantly change concrete and excavation quantities, especially on long runs. This calculator converts your layout into clear dimensions and volumes so you can plan materials and labor confidently.
2) Conduit count and spare capacity
Many projects add spare ducts for future loads, replacements, or reroutes. For example, adding two spares to an eight‑duct run increases total ducts by 25%. The tool treats spares exactly like working conduits, so the geometry and volumes reflect real build-out.
3) Outside diameter and clear spacing
Always use the conduit outside diameter from the product sheet. Clear spacing is the free gap between adjacent conduits. Typical clear values often fall in the 40–75 mm range (or 1.5–3 in), but your specification may require more for vibration, heat, or placement tolerances.
4) Side, top, and bottom cover
Concrete cover affects durability and mechanical protection. Increasing top cover from 75 mm to 100 mm adds height and raises concrete volume. Side cover also matters for rebar placement or formwork. Enter the cover values that match your detail drawings and local authority requirements.
5) Layout strategy: rows and columns
Auto layout balances rows and columns to avoid extreme shapes. Manual layout supports fixed configurations like 3×5 or 4×4 banks. If Rows × Columns exceeds total ducts, unused “slots” are treated as empty positions but the overall bank dimensions still follow your chosen grid.
6) Trench allowances that drive excavation
Trench width includes working space on both sides so crews can place forms, separators, and concrete safely. Trench depth combines duct bank height plus bedding thickness and soil cover above the bank. These three items often dominate excavation volume on deep installations.
7) Reading volume outputs
Concrete volume is bank width × bank height × length. Excavation volume is trench width × trench depth × length. Backfill is computed as excavation minus concrete, giving an immediate estimate for imported fill or re-use planning. Switch unit systems anytime to see outputs in m³ or yd³.
8) Waste factor and cost control
The waste factor multiplies volumes to cover overruns, spillage, over-excavation, and ordering buffers. A 5% waste on 20 m³ becomes 21 m³ for procurement. If you enter unit rates, the calculator estimates concrete and excavation costs, helping you compare options like tighter spacing versus fewer ducts per run.