Cables & circuits
Conduit fill calculator
Compare round cable cross-sectional area with a conduit’s usable internal area.
Result
Conduit cross-sectionReady
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Enter your values and press Calculate result.Formula
Area occupied = Σ (count × cable diameter²) ÷ inside diameter² × 100Within this model
Geometric area ratio for circular cables and a circular internal opening. Uses cable outside diameters including insulation. Area alone does not determine whether cables physically fit or can be pulled. No permitted fill percentage, UK cable-factor method, bend, thermal or installation assessment is included.
What the numbers mean
A circle has area πd²/4. Summing the cable areas and dividing by the conduit’s internal area gives the percentage occupied by cable material. Circular packing leaves gaps, so a result below 100% does not establish fit.
A worked example
Four cables of 5 mm outside diameter occupy 25% of the cross-sectional area of a 20 mm inside-diameter conduit.
Validation, precision and limitations