Conduit Fill Calculator

Calculate electrical conduit fill percentage, total conductor area, maximum wire count and recommended conduit size for raceway planning.

⚡ Field Rule: Conduit fill uses the outside diameter of the insulated conductor/cable, not only copper area. Use this with future Cable Tray Fill Calculator, Cable Derating Calculator, Earthing Conductor Size Calculator, plus existing Voltage Drop Calculator, Wire Gauge Calculator and Breaker Size Calculator.

🧰 Conduit Fill Check

Conductor Outside Diameter

Number of Conductors

Conduit Internal Diameter

Fill Rule

Custom Fill Limit

Wire Preset Optional

Conduit Preset Optional

Use actual conductor/cable outside diameter from the datasheet when available. Insulation type changes OD.

Presets:lighting circuitsocket circuitcontrol wires

Conductor Outside Diameter

Number of Conductors

Maximum Fill Limit

Conduit Series

Conduit Internal Diameter

Conductor Outside Diameter

Fill Limit

Reserve Extra Space

📐 Formula Reference

Wire Area

Wire area = π × (outside diameter ÷ 2)²

Total Wire Area

Total area = wire area × conductor count

Conduit Area

Conduit area = π × (internal diameter ÷ 2)²

Fill Percentage

Fill % = total wire area ÷ conduit internal area × 100

📋 Quick Reference

Common Fill Guide

1 conductor53%

2 conductors31%

3+ conductors40%

Must Check

Wire ODdatasheet

Conduit IDactual

Deratingseparate

Practical Notes

Many bendslarger size

Long pulllarger size

Future wiresreserve

📚 Engineering Notes

Fill is not ampacityConduit fill checks physical space. Current carrying capacity and grouping derating are separate checks.

Use actual outside diameterTwo cables with the same copper size can have different outside diameters depending on insulation and cable type.

Check voltage drop separatelyAfter choosing cable size and route length, use the Voltage Drop Calculator and Wire Gauge Calculator.

Next electrical checksFor full planning, use future Cable Tray Fill Calculator, Cable Derating Calculator and Earthing Conductor Size Calculator.

What is a Conduit Fill Calculator?

A conduit fill calculator estimates how much of a conduit’s internal cross-sectional area is occupied by electrical wires. It helps electricians and engineers choose a conduit size that is not overcrowded and is easier to pull.

How conduit fill is calculated

The calculator uses conductor outside diameter to calculate single wire area, multiplies it by the number of conductors, then compares the total with the internal area of the conduit.

Conduit sizing workflow

Choose wire size using the load current and Breaker Size Calculator. Check voltage drop with the Voltage Drop Calculator. Then use this page to check raceway fill. For larger installations, use the future Cable Tray Fill Calculator.

Important limitation

This calculator is a planning aid. Final installation must follow local electrical code, actual cable datasheets, conduit standards, derating rules, bend limits, pulling tension and site conditions.

❓ Frequently Asked Questions

No. Conduit fill should use the conductor or cable outside diameter, including insulation.

40% is commonly used for more than two conductors, but one or two conductors may have different limits. Always follow the applicable electrical code.

No. Fill checks physical space. Ampacity derating for grouping, ambient temperature and installation method is a separate calculation.