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🚇 Conduit Fill

How big a conduit do you need for your wires? Enter what you're pulling, get the smallest legal size.

Canada / CEC planning note: CEC Rule 12-910 and Table 8 use the same 53/31/40% fill percentages shown here. However, this tool still uses THHN/THWN conductor areas and NEC trade-size data because the Canadian Tables 6A–6K and 9 values have not passed our verification gate. Do not use its conduit-size result as the final basis for a Canadian installation; confirm it against the CEC or your inspection authority.

EMT is the common thin-wall metal tubing. PVC Sch 40 is the gray plastic conduit.

Sizes are for standard THHN/THWN insulated building wire — the most common single-conductor wire pulled in conduit.

wires

Count every insulated wire in the pipe, including the neutral and an insulated ground. All one size for now — mixed sizes coming.

The fill rules, in plain English

Conductors need free space in a conduit. The CEC Rule 12-910 / Table 8 limits are: one conductor may fill 53% of the pipe's inside area, two wires 31%, and three or more 40%. We do that area math for you using the official wire and conduit dimensions.

Good to know: long runs with many bends are easier with a size larger than the calculated minimum. For Canadian work, confirm conductor areas and metric trade sizes against CEC Tables 6A–6K and 9 before installation.