Conduit fill calculator

Preliminary estimate

Inputs

Group 1
Group 2
Calculation note

Default values are examples. Replace them with product dimensions and the fill target used for your review.

Method

Raceway area = pi x ID^2 / 4

Conductor area = count x pi x OD^2 / 4

Fill percent = total conductor area / raceway area x 100

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Formula variables

  • ID is raceway inside diameter in millimetres.
  • OD is conductor outside diameter in millimetres.
  • Count is the number of conductors in each group.
  • Target fill percent is selected by the user for preliminary review.

Assumptions

  • Use actual raceway inside diameter and conductor outside diameter from product data or the project reference table.
  • The selected fill target is a planning input for review, not an installation approval.
  • This calculator does not check conductor ampacity, derating, pulling tension, bend radius, conduit body fill, support spacing, product markings, or local authority requirements.
  • Confirm the current Canadian Electrical Code, provincial or territorial requirements, utility rules, manufacturer instructions, and AHJ direction before using results for work.

Examples

Mixed conductor group. Three conductors at 6 mm OD plus one conductor at 9 mm OD in a 27 mm inside-diameter raceway estimates about 25.9 percent fill.

Product-data workflow. If a raceway type or conductor insulation has a different actual diameter, use the manufacturer value instead of a nominal trade-size label.