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18 AWG Conduit Fill — Wires per Conduit Size

How many 18 AWG THHN conductors fit in EMT, IMC, RMC and PVC conduit, from 1/2 inch through 4 inch, with the 40% fill rule applied.

Quick answer

21 18 AWG THHN conductors fit in 1/2 inch EMT and 38 fit in 3/4 inch EMT, at 40% fill for three or more conductors. Each conductor consumes 0.0055 sq in from a nominal insulated outside diameter of 0.084 in. Neutrals and grounds count.

18 AWG conductors per conduit trade size

Same-size conductors only, at 53% for one, 31% for two and 40% for three or more.

Conduit1/2"3/4"1"1-1/4"1-1/2"2"2-1/2"3"3-1/2"4"
EMT213862107146200200200200200
IMC244269118160200200200200200
RMC223964110149200200200200200
PVC Sch 40203660104143200200200200200
PVC Sch 8015294989123200200200200200
Published standard — source: Raceway internal areas from product standards (EMT, IMC, RMC, PVC Sch 40, PVC Sch 80); conductor OD from nominal THHN dimensions

Source & method: Counts are the largest whole number where n × conductor area stays inside the raceway area times the applicable fill percentage. Mix conductor sizes in the calculator.

What each raceway type means

  • EMT — EMT (electrical metallic tubing)
  • IMC — IMC (intermediate metal conduit)
  • RMC — RMC (rigid metal conduit)
  • PVC Sch 40 — PVC Schedule 40
  • PVC Sch 80 — PVC Schedule 80

Frequently asked

How many 18 AWG wires fit in 1/2 inch EMT?
21 18 AWG THHN conductors fit in 1/2 inch EMT at the applicable fill percentage.
How many 18 AWG wires fit in 3/4 inch EMT?
38 conductors, using a nominal THHN outside diameter of 0.084 in and the 40% fill rule for three or more conductors.
Do neutrals and grounds count toward fill?
Yes, every conductor in the raceway counts for fill. Grounds are excluded only from the count of current-carrying conductors used for ampacity adjustment.
What is the cross-sectional area of 18 AWG THHN?
About 0.0055 square inches, from A = π × (OD / 2)² with a nominal insulated OD of 0.084 in.

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