General & Planning · CEC Section 12 & Table 6/10

Conduit Fill Calculator

Determine how many insulated conductors (THHN/THWN/T90) legally fit inside a conduit run based on the CEC 40% maximum fill rule.

Conduit Type

Trade Size of Conduit

Conductor Size (T90 / THHN Copper)

Number of Conductors in Conduit

CEC Table 6 (40% Rule)

MAX ALLOWABLE CONDUCTORS

9 Wires

CONDUIT FILL PERCENTAGE

18%

CEC DERATING THRESHOLD

80% Ampacity

Conduit Fill OK: Your wire count is well within the legal 40% fill limit.

For 3 or more current-carrying conductors in a single raceway, CEC Table 5C requires ampacity derating (80% for 4–6 wires).
1 conductor = max 53% fill, 2 conductors = max 31% fill, 3+ conductors = max 40% fill.
NMD90 / Romex sheath must be stripped or pulled in conduit using individual single conductors (T90/THHN) unless raceway is short protection sleeve.