Duct Bank Concrete Calculator
Order 7.03-7.44 yd³
Gross 200 ft³ − 17.45 ft³ conduit displacement = 182.55 ft³ (6.76 yd³ plan).
- Net concrete = bank cross-section × length − conduit displacement (π(d/2)² per conduit). Pure geometry.
- NRMCA CIP-8 ordering allowance (4-10%) applied: trench overbreak makes duct banks classic over-pour territory, and many estimators ignore displacement entirely and treat it as the allowance.
- Conduit spacers, encasement cover requirements, and red-oxide specs come from your utility/electrical spec; not computed here.
Why This One Is Different
A duct bank pour looks like a simple rectangular trench volume until you remember the conduits running through it don't hold concrete: they displace it, and skipping that subtraction is a common way estimates run high on paper and short at the truck. This calculator nets gross trench volume against the combined cross-sectional area of every conduit, times length, before applying the standard ordering allowance for overbreak and spillage. Cover depth, conduit spacing, and encasement strength are set by your utility's electrical spec, not by this page. Geometry is the only thing computed here.
Where the Numbers Come From
- Every conduit in the trench takes up space that would otherwise be concrete, and skipping that subtraction is a common way estimates run high: net concrete volume equals the bank's cross-section times length, minus the sum of each conduit's displacement (π × (diameter/2)² × length), straightforward geometry, but a step many hand estimates skip entirely. Source: duct-bank displacement geometry, engine convention, labeled
- NRMCA's standard guidance is to order 4-10% more than plan-derived volume for any formed pour, to cover subgrade irregularity, form deflection, and spillage: duct-bank trenches are a common case where this allowance alone gets treated as if it also covers displacement, which it doesn't. Source: NRMCA, CIP 8, Discrepancies in Yield
- Minimum cover depth over conduits, conduit-to-conduit spacing, and encasement compressive-strength requirements come from the National Electrical Safety Code and the specific utility's construction standard for the job, not from a concrete-volume calculator. Source: IEEE C2, National Electrical Safety Code
- Many estimators size a duct bank pour from gross trench dimensions alone and lean on the ordering allowance to absorb the conduit volume they never subtracted, a practice that works until the conduit count or diameter gets large enough to matter. Source: construction-estimating practitioner convention, labeled
More Questions
What sets the cover depth and spacing for conduits in a duct bank?
Your utility's construction standard and the National Electrical Safety Code, not this calculator. Those specs vary by voltage class and jurisdiction, so confirm them before you form the trench.
Related Calculators
Formulas, waste factors, and cost models on this page follow the sourced conventions on our methodology page. Estimates only; verify with your supplier and local code.