4" Rigid conduit fill

4" Rigid metal conduit (RMC, GRC) has an inside area of 12.882 sq in (4.050 in across). Three or more wires may take 40 % of it: 5.1528 sq in.

One wire, 53 %: 6.8275 sq in
Two wires, 31 %: 3.9934 sq in
Three or more, 40 %: 5.1528 sq in
Nipple, 60 %: 7.7292 sq in
Support: Every 10 ft, 3 ft from boxes
Sold in: 10 ft sticks

27 #1/0 THHN, the most it may hold, drawn to scale

How many wires fit in 4" Rigid

All wires the same size and type, by Annex C's method. For a mix of sizes, open the calculator.

Wire size	THHN/THWN-2	XHHW-2	THW/THW-2
14 AWG	531	370	370
12 AWG	387	284	284
10 AWG	244	212	212
8 AWG	140	118	118
6 AWG	101	87	71
4 AWG	62	63	53
3 AWG	53	53	45
2 AWG	44	45	38
1 AWG	33	33	27
1/0 AWG	27	28	23
2/0 AWG	23	23	19
3/0 AWG	19	19	16
4/0 AWG	16	16	14
250 kcmil	13	13	11
300 kcmil	11	11	9
350 kcmil	10	10	8
400 kcmil	8	9	7
500 kcmil	7	7	6
600 kcmil	6	6	5
700 kcmil	5	5	4
750 kcmil	5	5	4
800 kcmil	4	4	4
900 kcmil	4	4	3
1000 kcmil	4	4	3

Smaller: 3-1/2" Rigid Bigger: 5" Rigid

Other 4" conduit

Conduit	Inside area	#14	#12	#10	#8	#6
Rigid metal conduit (RMC, GRC)	12.882	531	387	244	140	101
Electrical metallic tubing	14.753	608	443	279	161	116
Intermediate metal conduit	13.631	562	410	258	149	107
Rigid PVC conduit, Schedule 40	12.554	517	377	238	137	99
Rigid PVC conduit, Schedule 80	11.258	464	338	213	123	89
Flexible metal conduit (FMC, Greenfield)	12.566	518	378	238	137	99
Liquidtight flexible metal conduit (LFMC)	12.692	523	381	240	138	100

About Rigid

Rigid (galvanized rigid conduit, GRC) has the thickest wall and the least room inside of the steel types. Support follows 344.30: within 3 ft of each box, then every 10 ft, or longer on straight runs with threaded couplings (Table 344.30(B)(2)). See strap spacing and the fill rules.