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Low Voltage Conduit Fill Calculator

Low Voltage Conduit Fill

Standard conduit fill calculators are built for electricians pulling THHN. They don't cover Cat6a, fire alarm, access control, or fiber optic cables. This calculator does. Select your cable types by category, enter quantities, and get an instant fill percentage against the 40% NEC limit. It handles mixed cable bundles, fire-rated sleeves, and OD-based calculations that low-voltage work actually requires. Built by LV contractors who run these numbers on every project.

Switch calculator

General EMT PVC Cat6 / DataLow VoltageFire Sleeves

Estimates based on NEC, NFPA, and IEEE standards. For reference only. Consult a licensed professional for critical design decisions.

Sleeve and Conduit Fill Tool

Free, NEC-compliant conduit fill calculator for electricians, low-voltage technicians, estimators, and engineers. Determine how many wires or cables safely fit inside various conduit types.

Conduit / Sleeve Type

Trade Size

Short nipple (≤24") — 60% fill

TipWe have a dedicated EMT Conduit Fill Calculator with specialized charts and reference tables.

Cable 1

Industry

Cable Type

Quantity

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Select your conduit and cables, then click Calculate

Quick Reference

Low Voltage Conduit Fill Chart

Maximum cable count per conduit size at 40% fill — computed from manufacturer cable OD data and NEC Chapter 9 formulas.

Cable	OD	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
Ethernet
Cat5e UTP	0.196"	4	7	11	19	26	44	77	117	153	195
Cat5e STP	0.225"	3	5	8	15	20	33	58	88	116	148
Cat6 UTP	0.24"	2	4	7	13	18	29	51	78	102	130
Cat6 STP	0.273"	2	3	5	10	13	22	40	60	78	100
Cat6a UTP	0.3"	1	3	4	8	11	18	33	50	65	83
Cat6a STP	0.276"	2	3	5	9	13	22	39	59	77	98
Cat8 S/FTP	0.335"	1	2	3	6	9	15	26	40	52	66
Fire Wire / Multi Conductor
14/2	0.201"	3	6	10	18	25	42	73	111	145	185
14/4	0.236"	2	4	7	13	18	30	53	80	105	134
16/2	0.166"	5	9	15	27	37	62	108	163	213	272
16/4	0.191"	4	7	12	20	28	46	81	123	161	205
18/2	0.151"	6	11	19	33	45	74	130	197	257	329
18/4	0.166"	5	9	15	27	37	62	108	163	213	272
22/2	0.132"	8	15	25	43	59	98	171	258	337	431
22/4	0.14"	7	13	22	38	52	87	152	229	299	383
22/6	0.178"	4	8	13	24	32	53	94	142	185	237
Access Control Cable
Composite Cable	0.415"	—	1	2	4	6	9	17	26	34	43
Shielded Composite	0.463"	—	1	2	3	4	7	13	21	27	35
18/4 Multi-Conductor	0.166"	5	9	15	27	37	62	108	163	213	272
18/2 Multi-Conductor	0.151"	6	11	19	33	45	74	130	197	257	329
22/2 Multi-Conductor	0.132"	8	15	25	43	59	98	171	258	337	431
22/4 Multi-Conductor	0.14"	7	13	22	38	52	87	152	229	299	383
22/6 Shielded	0.178"	4	8	13	24	32	53	94	142	185	237
Fiber (Aluminum Interlock)
6 strand	0.504"	—	1	1	2	4	6	11	17	23	29
12 strand	0.555"	—	—	1	2	3	5	9	14	19	24
24 strand	0.606"	—	—	1	2	2	4	8	12	16	20
48 strand	0.906"	—	—	—	—	1	2	3	5	7	9
72 strand	1"	—	—	—	—	1	1	2	4	5	7
Fiber (Un Armored tight buffer)
6 strand	0.2"	3	6	11	19	25	42	74	112	146	187
12 strand	0.24"	2	4	7	13	18	29	51	78	102	130
24 strand	0.31"	1	2	4	7	10	17	31	46	61	78
48 strand	0.66"	—	—	1	1	2	3	6	10	13	17
72 strand	0.79"	—	—	—	1	1	2	4	7	9	12
Fiber (Un Armored loose buffer)
6 strand	0.2"	3	6	11	19	25	42	74	112	146	187
12 strand	0.2"	3	6	11	19	25	42	74	112	146	187
24 strand	0.32"	1	2	4	7	10	16	29	43	57	73
48 strand	0.32"	1	2	4	7	10	16	29	43	57	73
72 strand	0.42"	—	1	2	4	5	9	16	25	33	42

Computed using NEC Chapter 9 area-based formula at 40% fill with manufacturer-published cable outside diameters. Values are for 3+ cables of the same type. Showing EMT conduit.

Cable	OD	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
Ethernet
Cat5e UTP	0.196"	4	7	11	19	26	44	77	117	153	195
Cat5e STP	0.225"	3	5	8	15	20	33	58	88	116	148
Cat6 UTP	0.24"	2	4	7	13	18	29	51	78	102	130
Cat6 STP	0.273"	2	3	5	10	13	22	40	60	78	100
Cat6a UTP	0.3"	1	3	4	8	11	18	33	50	65	83
Cat6a STP	0.276"	2	3	5	9	13	22	39	59	77	98
Cat8 S/FTP	0.335"	1	2	3	6	9	15	26	40	52	66
Fire Wire / Multi Conductor
14/2	0.201"	3	6	10	18	25	42	73	111	145	185
14/4	0.236"	2	4	7	13	18	30	53	80	105	134
16/2	0.166"	5	9	15	27	37	62	108	163	213	272
16/4	0.191"	4	7	12	20	28	46	81	123	161	205
18/2	0.151"	6	11	19	33	45	74	130	197	257	329
18/4	0.166"	5	9	15	27	37	62	108	163	213	272
22/2	0.132"	8	15	25	43	59	98	171	258	337	431
22/4	0.14"	7	13	22	38	52	87	152	229	299	383
22/6	0.178"	4	8	13	24	32	53	94	142	185	237
Access Control Cable
Composite Cable	0.415"	—	1	2	4	6	9	17	26	34	43
Shielded Composite	0.463"	—	1	2	3	4	7	13	21	27	35
18/4 Multi-Conductor	0.166"	5	9	15	27	37	62	108	163	213	272
18/2 Multi-Conductor	0.151"	6	11	19	33	45	74	130	197	257	329
22/2 Multi-Conductor	0.132"	8	15	25	43	59	98	171	258	337	431
22/4 Multi-Conductor	0.14"	7	13	22	38	52	87	152	229	299	383
22/6 Shielded	0.178"	4	8	13	24	32	53	94	142	185	237
Fiber (Aluminum Interlock)
6 strand	0.504"	—	1	1	2	4	6	11	17	23	29
12 strand	0.555"	—	—	1	2	3	5	9	14	19	24
24 strand	0.606"	—	—	1	2	2	4	8	12	16	20
48 strand	0.906"	—	—	—	—	1	2	3	5	7	9
72 strand	1"	—	—	—	—	1	1	2	4	5	7
Fiber (Un Armored tight buffer)
6 strand	0.2"	3	6	11	19	25	42	74	112	146	187
12 strand	0.24"	2	4	7	13	18	29	51	78	102	130
24 strand	0.31"	1	2	4	7	10	17	31	46	61	78
48 strand	0.66"	—	—	1	1	2	3	6	10	13	17
72 strand	0.79"	—	—	—	1	1	2	4	7	9	12
Fiber (Un Armored loose buffer)
6 strand	0.2"	3	6	11	19	25	42	74	112	146	187
12 strand	0.2"	3	6	11	19	25	42	74	112	146	187
24 strand	0.32"	1	2	4	7	10	16	29	43	57	73
48 strand	0.32"	1	2	4	7	10	16	29	43	57	73
72 strand	0.42"	—	1	2	4	5	9	16	25	33	42

Computed using NEC Chapter 9 area-based formula at 40% fill with manufacturer-published cable outside diameters. Values are for 3+ cables of the same type. Showing RMC conduit.

Cable	OD	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
Ethernet
Cat5e UTP	0.196"	4	7	11	19	26	44	63	98	131	168
Cat5e STP	0.225"	3	5	8	15	20	33	48	74	99	128
Cat6 UTP	0.24"	2	4	7	13	18	29	42	65	87	112
Cat6 STP	0.273"	2	3	5	10	13	22	32	50	67	86
Cat6a UTP	0.3"	1	3	4	8	11	18	27	41	55	72
Cat6a STP	0.276"	2	3	5	9	13	22	32	49	66	85
Cat8 S/FTP	0.335"	1	2	3	6	9	15	21	33	44	57
Fire Wire / Multi Conductor
14/2	0.201"	3	6	10	18	25	42	60	93	124	160
14/4	0.236"	2	4	7	13	18	30	43	67	90	116
16/2	0.166"	5	9	15	27	37	62	88	136	182	235
16/4	0.191"	4	7	12	20	28	46	66	103	138	177
18/2	0.151"	6	11	19	33	45	74	106	165	220	284
18/4	0.166"	5	9	15	27	37	62	88	136	182	235
22/2	0.132"	8	15	25	43	59	98	139	216	288	372
22/4	0.14"	7	13	22	38	52	87	124	192	256	330
22/6	0.178"	4	8	13	24	32	53	76	118	158	204
Access Control Cable
Composite Cable	0.415"	—	1	2	4	6	9	14	21	29	37
Shielded Composite	0.463"	—	1	2	3	4	7	11	17	23	30
18/4 Multi-Conductor	0.166"	5	9	15	27	37	62	88	136	182	235
18/2 Multi-Conductor	0.151"	6	11	19	33	45	74	106	165	220	284
22/2 Multi-Conductor	0.132"	8	15	25	43	59	98	139	216	288	372
22/4 Multi-Conductor	0.14"	7	13	22	38	52	87	124	192	256	330
22/6 Shielded	0.178"	4	8	13	24	32	53	76	118	158	204
Fiber (Aluminum Interlock)
6 strand	0.504"	—	1	1	2	4	6	9	14	19	25
12 strand	0.555"	—	—	1	2	3	5	7	12	16	21
24 strand	0.606"	—	—	1	2	2	4	6	10	13	17
48 strand	0.906"	—	—	—	—	1	2	2	4	6	7
72 strand	1"	—	—	—	—	1	1	2	3	5	6
Fiber (Un Armored tight buffer)
6 strand	0.2"	3	6	11	19	25	42	60	94	125	162
12 strand	0.24"	2	4	7	13	18	29	42	65	87	112
24 strand	0.31"	1	2	4	7	10	17	25	39	52	67
48 strand	0.66"	—	—	1	1	2	3	5	8	11	14
72 strand	0.79"	—	—	—	1	1	2	3	6	8	10
Fiber (Un Armored loose buffer)
6 strand	0.2"	3	6	11	19	25	42	60	94	125	162
12 strand	0.2"	3	6	11	19	25	42	60	94	125	162
24 strand	0.32"	1	2	4	7	10	16	23	36	49	63
48 strand	0.32"	1	2	4	7	10	16	23	36	49	63
72 strand	0.42"	—	1	2	4	5	9	13	21	28	36

Computed using NEC Chapter 9 area-based formula at 40% fill with manufacturer-published cable outside diameters. Values are for 3+ cables of the same type. Showing PVC Sch40 conduit.

Cable	OD	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"
Ethernet
Cat5e UTP	0.196"	3	5	9	17	23	39	56	87	117	152
Cat5e STP	0.225"	2	4	7	12	17	29	42	66	89	115
Cat6 UTP	0.24"	2	3	6	11	15	26	37	58	78	101
Cat6 STP	0.273"	1	2	4	8	12	20	28	45	60	78
Cat6a UTP	0.3"	1	2	4	7	10	16	23	37	50	65
Cat6a STP	0.276"	1	2	4	8	11	19	28	44	59	76
Cat8 S/FTP	0.335"	1	1	3	5	8	13	19	29	40	52
Fire Wire / Multi Conductor
14/2	0.201"	2	5	9	16	22	37	53	83	112	144
14/4	0.236"	2	3	6	11	16	27	38	60	81	105
16/2	0.166"	4	7	13	23	32	54	78	122	164	212
16/4	0.191"	3	6	10	17	24	41	59	92	124	160
18/2	0.151"	5	9	16	28	39	65	94	147	198	256
18/4	0.166"	4	7	13	23	32	54	78	122	164	212
22/2	0.132"	6	12	21	37	51	86	123	193	259	336
22/4	0.14"	6	11	18	33	45	76	110	171	230	298
22/6	0.178"	3	6	11	20	28	47	68	106	142	184
Access Control Cable
Composite Cable	0.415"	—	1	2	3	5	8	12	19	26	33
Shielded Composite	0.463"	—	1	1	3	4	7	10	15	21	27
18/4 Multi-Conductor	0.166"	4	7	13	23	32	54	78	122	164	212
18/2 Multi-Conductor	0.151"	5	9	16	28	39	65	94	147	198	256
22/2 Multi-Conductor	0.132"	6	12	21	37	51	86	123	193	259	336
22/4 Multi-Conductor	0.14"	6	11	18	33	45	76	110	171	230	298
22/6 Shielded	0.178"	3	6	11	20	28	47	68	106	142	184
Fiber (Aluminum Interlock)
6 strand	0.504"	—	—	1	2	3	5	8	13	17	23
12 strand	0.555"	—	—	1	2	2	4	7	10	14	19
24 strand	0.606"	—	—	—	1	2	4	5	9	12	15
48 strand	0.906"	—	—	—	—	1	1	2	4	5	7
72 strand	1"	—	—	—	—	—	1	2	3	4	5
Fiber (Un Armored tight buffer)
6 strand	0.2"	2	5	9	16	22	37	53	84	113	146
12 strand	0.24"	2	3	6	11	15	26	37	58	78	101
24 strand	0.31"	1	2	3	6	9	15	22	35	47	60
48 strand	0.66"	—	—	—	1	2	3	4	7	10	13
72 strand	0.79"	—	—	—	1	1	2	3	5	7	9
Fiber (Un Armored loose buffer)
6 strand	0.2"	2	5	9	16	22	37	53	84	113	146
12 strand	0.2"	2	5	9	16	22	37	53	84	113	146
24 strand	0.32"	1	2	3	6	8	14	21	32	44	57
48 strand	0.32"	1	2	3	6	8	14	21	32	44	57
72 strand	0.42"	—	1	2	3	5	8	12	19	25	33

Computed using NEC Chapter 9 area-based formula at 40% fill with manufacturer-published cable outside diameters. Values are for 3+ cables of the same type. Showing PVC Sch80 conduit.

Fire-Rated Reference

Fire-Rated Sleeve Fill Chart

Maximum cable count per fire-rated sleeve by cable outside diameter. These are UL-tested manufacturer values — not NEC area calculations.

Cable OD	EZD22	EZD33	EZD44+
0.118"22/2	80	352	868
0.138"22/4	63	266	648
0.157"18/2	42	192	483
0.177"18/4	35	154	378
0.197"Cat5e UTP	30	130	304
0.217"8 AWG THHN	20	108	255
0.236"Cat6 UTP	20	88	210
0.256"6 AWG THHN	12	70	168
0.276"Cat6a STP	12	63	156
0.315"Cat6a UTP	9	48	110
0.354"Cat8	6	35	90
0.394"Composite	6	30	72
0.433"Shielded Comp.	4	24	56
0.492"6-str Armor Fiber	4	20	42
0.591"12-str Armor Fiber	2	12	30
0.709"24-str Armor Fiber	1	6	20
0.787"48-str Armor Fiber	1	6	16
0.984"48-str Armor Fiber	1	4	9
1.181"72-str Armor Fiber	—	2	6
1.378"1000 kcmil	—	1	4

Source: STI EZPath cable transit data. EZD22/EZD33/EZD44+ device sizes. UL tested values.

Cable OD	Speed 2"	Speed 4"	Modular S	Modular M	Modular L
0.118"22/2	163	819	180	486	1188
0.138"22/4	121	596	144	368	851
0.157"18/2	88	451	112	280	660
0.177"18/4	69	356	84	216	522
0.197"Cat5e UTP	56	287	66	176	416
0.216"8 AWG THHN	45	240	50	150	360
0.236"Cat6 UTP	37	199	45	117	286
0.256"6 AWG THHN	32	164	32	96	240
0.275"Cat6a STP	27	141	28	88	198
0.314"Cat6a UTP	19	109	28	70	160
0.354"Cat8	16	85	18	54	126
0.394"Composite	13	61	15	40	104
0.433"Shielded Comp.	11	50	10	35	84
0.491"6-str Armor Fiber	7	38	8	24	60
0.59"12-str Armor Fiber	5	26	6	15	40
0.708"24-str Armor Fiber	3	19	3	12	28
0.786"48-str Armor Fiber	2	14	2	8	24
0.983"48-str Armor Fiber	1	8	2	6	15
1.179"72-str Armor Fiber	1	7	1	2	8
1.375"1000 kcmil	1	3	—	2	6

Source: Hilti published cable capacity data. Speed Sleeve (2"/4") and Modular Sleeve (S/M/L) sizes. Manufacturer tested values.

Reference

Supported Cable Types

All low-voltage cable categories supported in one calculator

Ethernet

Cat5e, Cat6, Cat6a

Fire Alarm

14/2, 16/2, 18/2

Access Control

Composite, 18/4

Fiber Optic

6 to 72 Strand

Technical Reference

Low Voltage Conduit Fill Guide

NEC fill rules, cable separation requirements, and fire-rated penetration sizing for low-voltage installations.

Why Low Voltage Contractors Need a Different Fill Calculator

Most conduit fill calculators are built for electricians pulling THHN. They reference NEC Table 5 wire areas and spit out conductor counts per conduit size. That doesn't help when you're pulling Cat6a, fire alarm cable, and access control wiring in the same conduit. Low-voltage cables aren't listed in NEC Table 5. Their fill is calculated from the cable's outside diameter, not a table lookup. A standard electrical fill calculator will give you wrong answers for every low-voltage cable type.

This calculator handles both methods: NEC table-based fill for electrical conductors and OD-based fill for low-voltage cables, so you can size conduit correctly regardless of what you're pulling. If your conduit carries only Ethernet cable and nothing else, the Cat6 Conduit Fill Calculator is faster — it's purpose-built for data-only runs with a detailed OD comparison chart for Cat5e, Cat6, Cat6a, and Cat6a STP.

NEC Article 725/760/770/800 vs Chapter 9: Which Rules Apply

NEC Chapter 9 governs raceway fill percentages: 53% for one conductor, 31% for two, 40% for three or more. Those percentages apply to all cables in conduit, including low-voltage. What changes is how you determine each cable's area. THHN uses Table 5. Class 2 cables (Article 725) like thermostat and access control wire use OD-based calculations. Fire alarm cables (Article 760) follow the same OD approach. Communications cables (Article 800) covering Cat5e through Cat8 also use OD. Fiber optic (Article 770) same thing. The fill percentage rule is universal. The cable area method depends on the article. Mix them up and your fill calculation is garbage.

Mixing Fire Alarm and Data Cable in the Same Conduit

Short answer: don't. NEC 760.136(B) prohibits power-limited fire alarm circuits from sharing raceways with communications circuits unless specific conditions are met. In practice, fire alarm cable runs in its own conduit, separate from data. The AHJ will fail your inspection if they find Cat6 and fire alarm cable in the same EMT. There are limited exceptions under 760.136(G) for cables with a listed common enclosure, but the safest approach is separate pathways. This matters for fill calculations because you need to size two conduits instead of one. Plan your pathway routing accordingly, especially in tight ceiling spaces where running parallel conduits gets expensive.

Cable OD-Based Calculation vs NEC Area-Based

Two different methods, same goal. For THHN and other electrical conductors, NEC Table 5 gives you the exact cross-sectional area in square inches. You add them up and compare against Table 4 conduit areas. Done. For low-voltage cables, there is no Table 5 entry. You measure or look up the cable's OD from the manufacturer, calculate the area using the formula (π × (OD/2)²), then compare against the same Table 4 conduit areas. The 40% fill limit applies identically to both methods. Where it gets tricky is mixed conduit with both electrical and low-voltage cables.

NEC 300.3(C)(1) generally prohibits this, but when it's allowed, you need to add Table 5 areas for electrical conductors and OD-calculated areas for LV cables. This calculator handles both automatically.

Fire-Rated Penetrations for Low Voltage Cable Bundles

Every conduit or cable bundle that passes through a fire-rated wall or floor needs a listed firestop system. For conduit penetrations, the annular space around the conduit gets packed with fire caulk or putty per the manufacturer's UL listing. For cable bundles on tray or J-hooks, you need a listed device like an STI EZPath or Hilti speed sleeve. These devices have their own fill limits that are separate from conduit fill. An STI EZPath 2-gang device holds a specific number of cables based on OD, and those numbers don't follow the 40% conduit rule.

This calculator includes fire-rated sleeve fill tables so you can size both your conduit runs and your firestop penetrations from the same tool. Getting the penetration wrong is a code violation that gets caught on final inspection and costs real money to fix.

Common Questions

Frequently Asked Questions

At minimum, two separate conduits: one for fire alarm and one for everything else. NEC 760.136(B) requires fire alarm circuits to be separated from communications cables. Your Cat6a and access control cables can share a conduit since both are low-voltage and don't conflict under NEC Articles 725 and 800. Size the fire alarm conduit based on your 14/2 or 16/2 FPLR cable count and OD. Size the data/access control conduit for your combined Cat6a and 18/4 cable count. Run both through this calculator separately to get correct fill percentages for each pathway.

Add up the cross-sectional areas individually. Each cable type contributes π × (OD/2)² to the total. Say you have 8 Cat6a (0.30" OD = 0.071 sq in each), 4 access control 18/4 (0.24" OD = 0.045 sq in each), and 2 composite reader cables (0.38" OD = 0.113 sq in each). Total area: (8 × 0.071) + (4 × 0.045) + (2 × 0.113) = 0.568 + 0.180 + 0.226 = 0.974 sq inches. At 40% fill, you need a conduit with at least 2.435 sq inches of internal area, which is 2" EMT (3.356 sq in internal). This calculator does this math automatically when you add multiple cable types.

A 24-strand single-mode indoor/outdoor fiber cable typically runs 0.50-0.60" OD depending on the jacket type and manufacturer. At 0.55" OD, the cable area is 0.238 sq inches. At 40% fill with a single cable, you'd technically need only 1/2" EMT. But fiber in conduit has special considerations: you need to maintain minimum bend radius (typically 10x the cable OD for single-mode), and you want room for a pull rope and potentially a second cable in the future. We recommend 1" EMT minimum for any fiber conduit run, regardless of what the fill calculation says. For outdoor underground runs, use PVC Schedule 40 with sweeping radius fittings and innerduct to protect the fiber.

Most fire alarm risers use 14/2 FPLR or 16/2 FPLR cable. A 14/2 FPLR cable runs about 0.25" OD (0.049 sq in area). For a typical floor with 8 notification appliance circuits and 4 initiating device circuits, you're looking at 12 cables. At 40% fill: 12 × 0.049 = 0.589 sq inches of cable area, requiring 1.47 sq inches of conduit area. That's 1" EMT (0.864 sq in internal) at 68% fill, well over the limit. You need 1-1/4" EMT (1.496 sq in internal) at 39% fill. If you're also running SLC loops and audio circuits for voice evac, bump to 1-1/2" EMT to leave room for growth.

Yes to PVC underground, and the fill percentage stays the same (40% for three or more cables) but the conduit internal dimensions differ from EMT. PVC Schedule 40 has thicker walls than EMT, so the internal area is slightly smaller for the same trade size. A 1" PVC Schedule 40 has 0.688 sq inches internal area versus 0.864 sq inches for 1" EMT. That means fewer cables fit. PVC Schedule 80 is even smaller at 0.581 sq inches for 1" trade size. Always select the correct conduit type in this calculator. Using EMT dimensions for a PVC installation will give you an undersized conduit. For direct burial, also check NEC 300.5 for minimum cover depth requirements.

Security camera systems use the same Cat6 or Cat6a cable as data networks, so the fill calculation is identical. Twenty Cat6 cables (0.25" OD) need: 20 × 0.049 = 0.982 sq inches of cable area. At 40% fill, you need 2.455 sq inches of conduit area, which is 2" EMT (3.356 sq in internal) at 29% fill. If you're running Cat6a for cameras that need PoE++ (60W+), the larger OD pushes you to: 20 × 0.071 = 1.414 sq inches, still fitting in 2" EMT at 42%, technically over by 2%. Jump to 2-1/2" EMT to be safe. Camera systems grow fast; most facilities add 30-50% more cameras within 3 years. Size your conduit for 30 cables even if you're only pulling 20 today.

The conduit fill percentage doesn't change based on the space rating. NEC 40% fill applies everywhere. What changes is the cable jacket type, which affects OD. Plenum-rated (CMP) cables have jackets made from low-smoke materials that tend to be 0.01-0.03" thicker than riser-rated (CMR) equivalents. Over a bundle of 12 cables, those extra thousandths add up to roughly 8-12% more total area. The bigger issue is that in plenum spaces, you may not need conduit at all. NEC 800.154 allows plenum-rated cables to be run without conduit in plenum spaces.

If your cables are plenum-rated and the run is in a return air ceiling, J-hooks or cable tray might save significant labor and material cost compared to conduit.

Fiber, Cat6a, and coax can share a conduit because all three are low-voltage communications cables under NEC Articles 770, 800, and 820 respectively. The fill calculation needs each cable's OD: Cat6a UTP at 0.30", RG6 coax at 0.27", and fiber cable OD varies widely from 0.20" for a 6-strand to 0.60"+ for a 48-strand. For a typical AV rough-in with 4 Cat6a, 2 RG6, and 1 twelve-strand fiber (0.35" OD): (4 × 0.071) + (2 × 0.057) + (1 × 0.096) = 0.284 + 0.114 + 0.096 = 0.494 sq inches. At 40% fill you need 1.235 sq inches of conduit, which is 1-1/4" EMT (1.496 sq in) at 33% fill. Leave room for the HDMI-over-fiber or USB cables that always get added after the initial install.

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APA Citation

TSS USA. (2025). Low Voltage Conduit Fill Calculator. Retrieved from https://tssusa.net/low-voltage-conduit-fill-calculator/

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Last Updated: June 1, 2025

Fill calculations use cable outside diameter (OD) to derive cross-sectional area for low-voltage cables (Ethernet, fire alarm, access control, fiber optic), compared against conduit internal area at the 40% NEC fill limit. Cable OD values sourced from manufacturer specifications. Conduit internal dimensions per NEC Chapter 9, Table 4. Fire-rated sleeve capacities from STI and Hilti published UL-tested data.

Standards & References

NFPA 70 — National Electrical Code (NEC) — Articles 725, 760, 800 — low-voltage, fire alarm, and communications cable requirements
NFPA 72 — National Fire Alarm and Signaling Code — Fire alarm cable installation requirements
BICSI — Low-voltage cabling installation standards

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