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.

18 AWG Conduit Fill by Conduit Size

How many 18 AWG THHN conductors fit in EMT, IMC, RMC and PVC conduit, 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.

Conduit	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
EMT	21	38	62	107	146	200	200	200	200	200
IMC	24	42	69	118	160	200	200	200	200	200
RMC	22	39	64	110	149	200	200	200	200	200
PVC Sch 40	20	36	60	104	143	200	200	200	200	200
PVC Sch 80	15	29	49	89	123	200	200	200	200	200

Published standard

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.

Fill behaviour at 18 AWG: count is never the constraint

18 AWG is small enough that raceway area is effectively unlimited for any realistic circuit. Even the smallest trade size accepts far more 18 AWG conductors than a control or signal circuit ever needs, so the practical limits are elsewhere: conductor-count derating, box fill at the terminations, and how many conductors you can actually terminate in the device.

This size is used for fixture wire, control wiring, thermostat and low-voltage class circuits rather than power branch circuits. When an 18 AWG raceway pull gets crowded, the reason is usually that dozens of control conductors share one home run, and the correct answer is a wireway or a larger tube rather than squeezing the fill percentage.

Source & method: Counts referenced above come from the computed table on this page — how these numbers are derived.

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

Full fill charts by raceway

Per-type counts for every trade size, plus the cross-type comparison and reverse lookup.

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.

Conduit fill for nearby sizes

Same 40% fill rule applied to the sizes either side of this one, wrapping around the range so every size is reachable.