Conduit Fill Calculator (NEC Chapter 9): EMT, PVC, Rigid

Updated 2026-09-29

Short answer: add up the area of every conductor (NEC Chapter 9, Table 5) and compare it with 40% of the conduit's internal area (Table 4) for three or more wires. If it is under, the conduit is big enough.

The 40% rule

Conductors	Maximum fill
1	53%
2	31%
3 or more	40%
Nipple 24" or shorter	60%

Quick table: maximum THHN in EMT

Wire	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"
#14 THHN	12	22	35	61	84	138
#12 THHN	9	16	26	45	61	101
#10 THHN	5	10	16	28	38	63
#8 THHN	3	6	9	16	22	36
#6 THHN	2	4	7	12	16	26

For PVC, rigid, other wire types and every size up to 4", see the full conduit fill chart.

How conduit fill is calculated

Look up each conductor's area in Chapter 9, Table 5 (for example #12 THHN = 0.0133 in²).
Add them up. Nine #12 THHN = 0.1197 in².
Look up the conduit's internal area in Table 4 (1/2" EMT = 0.304 in²) and take the allowed percentage: 40% of 0.304 = 0.1216 in².
Compare. 0.1197 ≤ 0.1216, so nine #12 THHN fit.

Note 7 rounding

When every conductor is the same size, a result such as 8.8 wires may be rounded up to 9 (Chapter 9, Note 7). The calculator and the tables on this site apply that rule, so they match the NEC Annex C tables.

Things the fill percentage does not tell you

Ampacity adjustment: more than three current-carrying conductors in a raceway need derating (310.15(C)(1)).
Jamming: three conductors in a conduit with an inside-diameter-to-conductor ratio between 2.8 and 3.2 can jam on a pull around bends.
Pull tension: a run at 40% with several bends can still be a hard pull; keep bends under 360° between pull points.

Questions electricians ask

How many 12 AWG wires can go in 1/2 EMT?

Nine #12 THHN/THWN-2 conductors fit in 1/2" EMT at 40% fill. With XHHW it is 6, and with THW it is 4, because the insulation is thicker.

How many 12 AWG wires can go in 3/4 EMT?

Sixteen #12 THHN conductors fit in 3/4" EMT. For #10 THHN it is 10 and for #14 THHN it is 22.

What is the 40% conduit fill rule?

NEC Chapter 9, Table 1 allows conductors to take up 40% of the conduit's internal area when there are three or more. One conductor may take 53% and two conductors 31%; nipples 24" or shorter may be filled to 60%.

Does the ground wire count toward conduit fill?

Yes. Equipment grounding and bonding conductors count toward conduit fill (Chapter 9, Note 3), using their actual area; a bare ground uses the bare conductor area from Table 8.

What is Note 7?

Chapter 9, Note 7 says that when all conductors are the same size, a calculated count ending in .8 or more may be rounded up to the next whole number. That is why the published tables sometimes allow one more wire than straight division gives.