What is the maximum conduit fill percentage?

40% of the conduit's internal cross-sectional area for three or more conductors, 31% for exactly two conductors and 53% for a single conductor. Nipples 24 inches or shorter are permitted at 60%.

How do I read this fill chart?

Pick the conduit type, find the row for your conductor size and read across to the trade size. The number is how many same-size THHN conductors the raceway holds at the applicable fill percentage — for 12 AWG in 1/2 inch EMT that is 9. Count every current-carrying conductor plus the equipment grounding conductor. Each wire size links to its own conduit-fill page for the full per-size breakdown.

Does the ground wire count toward conduit fill?

Yes. Every conductor in the raceway counts for fill, including the equipment grounding conductor and the neutral. Grounds are excluded only from ampacity derating counts, not from fill.

Why does PVC Schedule 80 hold fewer wires?

Schedule 80 has the same outside diameter as Schedule 40 but a thicker wall, so the internal diameter and usable area are smaller. Expect roughly 15 to 25% fewer conductors for the same trade size.

Is more than 40% fill ever allowed?

Only for short nipples of 24 inches or less, which are permitted at 60% fill. Ordinary raceway runs stay at 40%, and exceeding it makes pulling difficult and traps heat around the conductors.

How do I find the smallest conduit for a conductor count?

Work the chart backwards: read down the trade-size columns on your conductor's row until the count meets or exceeds what you are pulling. Six 12 AWG THHN, for example, lands at 1/2 inch EMT and 1/2 inch PVC Schedule 40. The reverse-lookup table below does this for every size.

Should I fill conduit to exactly 40%?

No. Forty percent is the legal ceiling, not a design target. Pulls with more than 180 degrees of total bend, runs longer than about 100 ft between pull points, and raceways likely to gain circuits later are normally sized one trade size up so the pull is achievable and there is spare capacity.

Conduit Fill Chart — All Conduit Types

Maximum conductor count per trade size, computed from published raceway internal diameters and nominal THHN outside diameters.

Quick answer

Fill limits are 40% of internal area for three or more conductors, 31% for two, 53% for one, and 60% for nipples 24 inches or shorter. The conductor count at a given trade size depends on wall thickness, so the same 1/2 inch trade size holds 9 12 AWG THHN in thin-wall tubing but only 6 in the thickest-wall PVC. Grounds and neutrals count.

By conduit type

Each raceway family has its own chart with per-type counts, areas and worked examples.

EMT fill chart — THHN/THWN-2

Maximum number of same-size conductors at the applicable fill percentage. Mixed sizes need the calculator.

Wire size	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
14 AWG	12	22	35	61	84	138	242	365	401	401
12 AWG	9	16	26	45	61	101	176	266	347	401
10 AWG	5	10	16	28	38	63	110	167	218	279
8 AWG	3	5	9	16	22	36	63	96	126	161
6 AWG	1	4	6	11	16	26	46	69	91	116
4 AWG	1	2	4	7	9	16	28	42	56	71
3 AWG	1	1	3	6	8	13	24	36	47	60
2 AWG	1	1	2	5	7	11	20	30	39	50
1 AWG	1	1	1	3	5	8	14	22	29	37
1/0 AWG	—	1	1	3	4	7	12	19	24	31
2/0 AWG	—	1	1	2	3	6	10	15	20	26
3/0 AWG	—	1	1	1	3	5	8	13	17	22
4/0 AWG	—	—	1	1	1	4	7	10	14	18

EMT (electrical metallic tubing)

Published standard

Source & method: Counts are computed as floor(usable area / conductor area) with the fill percentage that matches the resulting count. Nothing is copied from a code table.

Raceway internal area by trade size

Trade size	EMT	IMC	RMC	PVC 40	PVC 80
1/2"	0.304 (0.122)	0.342 (0.137)	0.314 (0.125)	0.285 (0.114)	0.217 (0.087)
3/4"	0.533 (0.213)	0.586 (0.235)	0.549 (0.220)	0.508 (0.203)	0.409 (0.164)
1"	0.864 (0.346)	0.959 (0.384)	0.887 (0.355)	0.832 (0.333)	0.688 (0.275)
1-1/4"	1.496 (0.598)	1.647 (0.659)	1.526 (0.610)	1.453 (0.581)	1.237 (0.495)
1-1/2"	2.036 (0.814)	2.225 (0.890)	2.071 (0.829)	1.986 (0.794)	1.711 (0.684)
2"	3.356 (1.342)	3.631 (1.452)	3.408 (1.363)	3.291 (1.316)	2.874 (1.150)
2-1/2"	5.858 (2.343)	5.135 (2.054)	4.866 (1.946)	4.695 (1.878)	4.119 (1.647)
3"	8.846 (3.538)	7.922 (3.169)	7.499 (3.000)	7.268 (2.907)	6.442 (2.577)
3-1/2"	11.545 (4.618)	10.584 (4.234)	10.010 (4.004)	9.737 (3.895)	8.688 (3.475)
4"	14.753 (5.901)	13.631 (5.452)	12.883 (5.153)	12.554 (5.022)	11.258 (4.503)

Total internal cross-sectional area, square inches, and the 40% usable figure.

Conductor outside diameters used

Size	Insulated OD (in)	Area (sq in)
18 AWG	0.084	0.0055
16 AWG	0.096	0.0072
14 AWG	0.111	0.0097
12 AWG	0.130	0.0133
10 AWG	0.164	0.0211
8 AWG	0.216	0.0366
6 AWG	0.254	0.0507
4 AWG	0.324	0.0824
3 AWG	0.352	0.0973
2 AWG	0.384	0.1158
1 AWG	0.446	0.1562
1/0 AWG	0.486	0.1855
2/0 AWG	0.532	0.2223
3/0 AWG	0.581	0.2651
4/0 AWG	0.642	0.3237
250 kcmil	0.711	0.3970
300 kcmil	0.766	0.4608
350 kcmil	0.817	0.5242
400 kcmil	0.864	0.5863
500 kcmil	0.949	0.7073
600 kcmil	1.051	0.8676
750 kcmil	1.158	1.0532

Nominal THHN/THWN-2 insulated outside diameter and the area each conductor consumes.

How to use the conduit fill table by conduit type

Every conduit fill table works the same way. Take the internal area of the raceway, multiply it by the allowed percentage, then divide by the area of one insulated conductor. That is all the electrical conduit fill chart above is doing — the tables are pre-solved so you can read the number of wires straight off the row for your trade size.

Conduit type changes the answer even at the same trade size, because the wall thickness differs. Metal conduit splits three ways: EMT has the thinnest wall and the most room, IMC is slightly tighter, and rigid metal conduit (RMC) is tighter again. On the plastic side, PVC Schedule 40 is close to IMC, while Schedule 80 has the thickest wall and holds roughly 15 to 25% fewer conductors. A pipe fill chart written for water pipe is not interchangeable — trade sizes share names, not internal diameters.

Type-specific worked examples live on the per-type charts, because the numbers diverge as soon as you name a raceway: the same six 12 AWG conductors need a different trade size in thin-wall tubing than in Schedule 80. Pick the raceway you are actually installing from the type links above, or use the calculator for mixed sizes.

Two counting rules trip people up. For fill, every conductor in the raceway counts — hots, neutral and the equipment grounding conductor. For ampacity derating, only current-carrying conductors count, so the ground is excluded and, in most balanced systems, so is the neutral. Fill and derating are separate calculations run on the same pull, and the stricter one governs the design.

Reverse lookup — smallest conduit for a given conductor count

Read down your wire size, across to the number of conductors in the pull, and the cell gives the smallest trade size that stays inside the fill limit.

Wire size	2 wires	3 wires	4 wires	6 wires	9 wires	12 wires	16 wires	20 wires
14 AWG	1/2"	1/2"	1/2"	1/2"	1/2"	1/2"	3/4"	3/4"
12 AWG	1/2"	1/2"	1/2"	1/2"	1/2"	3/4"	3/4"	1"
10 AWG	1/2"	1/2"	1/2"	3/4"	3/4"	1"	1"	1-1/4"
8 AWG	1/2"	1/2"	3/4"	1"	1"	1-1/4"	1-1/4"	1-1/2"
6 AWG	3/4"	3/4"	3/4"	1"	1-1/4"	1-1/2"	1-1/2"	2"
4 AWG	3/4"	1"	1"	1-1/4"	1-1/2"	2"	2"	2-1/2"
3 AWG	1"	1"	1-1/4"	1-1/4"	2"	2"	2-1/2"	2-1/2"
2 AWG	1"	1-1/4"	1-1/4"	1-1/2"	2"	2-1/2"	2-1/2"	2-1/2"
1 AWG	1-1/4"	1-1/4"	1-1/2"	2"	2-1/2"	2-1/2"	3"	3"
1/0 AWG	1-1/4"	1-1/4"	1-1/2"	2"	2-1/2"	2-1/2"	3"	3-1/2"
2/0 AWG	1-1/4"	1-1/2"	2"	2"	2-1/2"	3"	3-1/2"	3-1/2"
3/0 AWG	1-1/2"	1-1/2"	2"	2-1/2"	3"	3"	3-1/2"	4"
4/0 AWG	2"	2"	2"	2-1/2"	3"	3-1/2"	4"	—

Smallest EMT trade size, in inches, for N same-size THHN conductors at the applicable fill percentage.

Source & method: Solved by walking the trade sizes from smallest to largest and returning the first one whose usable area covers the conductor bundle. A dash means no listed trade size in this conduit type holds that many conductors of that size. Counts include the equipment grounding conductor, so a 20 A circuit with two hots, a neutral and a ground is 4 wires.

Mixed conductor sizes and the practical limits

The tables on this page assume every conductor in the raceway is the same size, which covers most branch circuits. When sizes are mixed — say three 6 AWG phases with a 10 AWG ground — add the individual conductor areas from the outside-diameter table above, then compare the total against the usable area for the total conductor count. The conduit fill calculator does that arithmetic for you.

Fill is a legal ceiling, not a target. A raceway at exactly 40% with four 90 degree bends is close to unpullable without damaging insulation, and long pulls need lubricant and rope tension the same fill number cannot see. Designers commonly size one trade size up when a run has more than 180 degrees of total bend, exceeds about 100 ft between pull points, or is likely to gain circuits later. Spare capacity in a raceway is far cheaper than a second raceway.

Insulation type also moves the count. The tables use THHN/THWN-2, the thinnest common building-wire insulation. Thicker jackets such as XHHW or USE, and any conductor with an outer nylon plus PVC assembly heavier than THHN, take more area per conductor and drop the count. If a spec calls out an insulation other than THHN, substitute its published outside diameter into the same area math rather than reusing these numbers.

Frequently asked

What is the maximum conduit fill percentage?: 40% of the conduit's internal cross-sectional area for three or more conductors, 31% for exactly two conductors and 53% for a single conductor. Nipples 24 inches or shorter are permitted at 60%.
How do I read this fill chart?: Pick the conduit type, find the row for your conductor size and read across to the trade size. The number is how many same-size THHN conductors the raceway holds at the applicable fill percentage — for 12 AWG in 1/2 inch EMT that is 9. Count every current-carrying conductor plus the equipment grounding conductor. Each wire size links to its own conduit-fill page for the full per-size breakdown.
Does the ground wire count toward conduit fill?: Yes. Every conductor in the raceway counts for fill, including the equipment grounding conductor and the neutral. Grounds are excluded only from ampacity derating counts, not from fill.
Why does PVC Schedule 80 hold fewer wires?: Schedule 80 has the same outside diameter as Schedule 40 but a thicker wall, so the internal diameter and usable area are smaller. Expect roughly 15 to 25% fewer conductors for the same trade size.
Is more than 40% fill ever allowed?: Only for short nipples of 24 inches or less, which are permitted at 60% fill. Ordinary raceway runs stay at 40%, and exceeding it makes pulling difficult and traps heat around the conductors.
How do I find the smallest conduit for a conductor count?: Work the chart backwards: read down the trade-size columns on your conductor's row until the count meets or exceeds what you are pulling. Six 12 AWG THHN, for example, lands at 1/2 inch EMT and 1/2 inch PVC Schedule 40. The reverse-lookup table below does this for every size.
Should I fill conduit to exactly 40%?: No. Forty percent is the legal ceiling, not a design target. Pulls with more than 180 degrees of total bend, runs longer than about 100 ft between pull points, and raceways likely to gain circuits later are normally sized one trade size up so the pull is achievable and there is spare capacity.