PVC Conduit Fill Chart: NEC Chapter 9 Limits for Schedule 40 & 80

Every underground feeder job reaches the same moment. The trench is open, the sweeps are glued, and somebody asks how many 4/0 will fit in the 3 inch. Half the crew reaches for a phone app, one guy says “four, always four,” and nobody opens the book. Four is right for Schedule 40. It is wrong for Schedule 80, and that is the kind of miss that gets caught after the concrete goes down.

Conduit fill trips people up because the limit is not a single number and the chart is not a single chart. NEC Chapter 9 Table 1 sets the percentage, Table 4 gives each raceway its internal area, Table 5 gives each conductor its area, and Annex C turns all three into a finished count — but only when every conductor in the pipe is the same size. Schedule 40 and Schedule 80 PVC share a trade size and do not share an inside diameter, so they never share a column.

This guide gives you the PVC conduit fill chart for both Schedule 40 and Schedule 80 with THHN/THWN-2, shows where the numbers come from in Chapter 9, walks the calculation for mixed conductor sizes, and covers the Article 352 rules that decide where the pipe is legal in the first place.

What conduit fill actually limits — NEC Chapter 9 Table 1

Fill is a cross-sectional area problem. Take the inside area of the pipe, take the total area of everything you are putting in it, and the second number must stay under a fixed percentage of the first. NEC Chapter 9 Table 1 sets that percentage by conductor count:

• 1 conductor — 53%. A single conductor sits in the middle and has room around it.
• 2 conductors — 31%. Two round conductors in a round pipe waste the most space, so the allowance drops.
• Over 2 conductors — 40%. The number that governs almost every real circuit you will ever pull.

Three tables feed the answer. Chapter 9 Table 4 gives the internal area of every raceway in square inches, broken out by type — and rigid PVC gets separate blocks for Schedule 40, Schedule 80, Type A and Type EB. Chapter 9 Table 5 gives the approximate area of each insulated conductor by size and insulation type. Annex C is the pre-solved version of both, for the single case where every conductor is identical.

Why the limit is 40% and not something higher

The 40% figure is not about whether the wire physically fits. Jam ratio, pulling tension and heat all get worse long before the pipe is full. Above 40% the conductors bind on the bends, the jacket abrades, and the air space that lets a bundle shed heat disappears. The ampacity values in Table 310.16 assume that air space exists.

Fill and derating are separate obligations and people collapse them constantly. Staying under 40% does not exempt you from the adjustment factors in 310.15(C)(1) once more than three current-carrying conductors share the raceway. You can pass fill and still be over on ampacity.

Schedule 40 vs Schedule 80 PVC — why the charts differ

Both schedules share the same outside diameter at a given trade size, because both have to accept the same fittings. Schedule 80 gets its physical-damage rating from a thicker wall, and that wall is taken out of the inside. The result is a pipe that looks identical on the rack and holds noticeably less:

Areas are from NEC Chapter 9 Table 4, Article 352 Rigid PVC Conduit. The penalty is worst in the small sizes, where the wall thickness is a bigger share of the bore — a 1/2 inch Schedule 80 loses nearly a quarter of its usable area, while a 4 inch loses about a tenth.

PVC conduit fill chart — Schedule 40, THHN/THWN-2

This is the chart most electricians are looking for: maximum number of THHN/THWN-2 conductors, all the same size, in Rigid PVC Schedule 40. It corresponds to NEC Annex C Table C.10.

Wire size	1/2″	3/4″	1″	1-1/4″	1-1/2″	2″	2-1/2″	3″	4″
14 AWG	11	21	34	60	82	135	193	299	517
12 AWG	8	15	25	43	59	99	141	218	377
10 AWG	5	9	15	27	37	62	89	137	238
8 AWG	3	5	9	16	21	36	51	79	137
6 AWG	1	4	6	11	15	26	37	57	99
4 AWG	1	2	4	7	9	16	22	35	61
3 AWG	1	1	3	6	8	13	19	30	51
2 AWG	1	1	3	5	7	11	16	25	43
1 AWG	—	1	1	3	5	8	12	18	32
1/0 AWG	—	1	1	3	4	7	10	15	27
2/0 AWG	—	1	1	2	3	6	8	13	22
3/0 AWG	—	1	1	1	3	5	7	11	18
4/0 AWG	—	—	1	1	2	4	6	9	15
250 kcmil	—	—	1	1	1	3	4	7	12
350 kcmil	—	—	—	1	1	2	3	5	9
500 kcmil	—	—	—	1	1	1	2	4	7

PVC conduit fill chart — Schedule 80, THHN/THWN-2

Same conductors, same percentages, smaller pipe. This corresponds to NEC Annex C Table C.9:

Wire size	1/2″	3/4″	1″	1-1/4″	1-1/2″	2″	2-1/2″	3″	4″
14 AWG	9	17	28	51	70	118	170	265	464
12 AWG	6	12	20	37	51	86	124	193	338
10 AWG	4	7	13	23	32	54	78	122	213
8 AWG	2	4	7	13	18	31	45	70	123
6 AWG	1	3	5	9	13	22	32	51	89
4 AWG	1	1	3	6	8	14	20	31	54
3 AWG	1	1	3	5	7	12	17	26	46
2 AWG	—	1	2	4	6	10	14	22	39
1 AWG	—	1	1	3	4	7	10	16	29
1/0 AWG	—	1	1	2	3	6	9	14	24
2/0 AWG	—	—	1	1	3	5	7	11	20
3/0 AWG	—	—	1	1	2	4	6	9	17
4/0 AWG	—	—	1	1	1	3	5	8	14
250 kcmil	—	—	—	1	1	3	4	6	11
350 kcmil	—	—	—	1	1	1	3	5	8
500 kcmil	—	—	—	—	1	1	2	3	6

When the conductors are not all the same size — the five-step calculation

The moment your raceway holds two different sizes — three 2/0 phases and a 4 AWG ground, say — Annex C is off the table and you calculate. This is the method inspectors expect to see on a submittal.

Step 1 — count every conductor going in. Phases, neutral, equipment grounding conductor, isolated ground, control wires. If it occupies space in the pipe, it is in the calculation.

Step 2 — look up each conductor’s area in Chapter 9 Table 5. Use the row for the actual insulation type. THHN/THWN-2 is the smallest common building wire; XHHW-2 and RHH run larger, and substituting them silently can push a borderline pull over the line.

Step 3 — multiply and total. Quantity times area for each size, then add the products. Three 2/0 THHN at 0.2223 is 0.6669, plus one 4 AWG THHN at 0.0824, for 0.7493 in².

Step 4 — apply the Table 1 percentage. Four conductors means 40%. Divide the total by 0.40 to get the minimum internal area the pipe must have: 0.7493 ÷ 0.40 = 1.873 in².

Step 5 — pick the trade size from Table 4. Schedule 40 at 1-1/2 inch is 1.986 in², which clears it. Schedule 80 at 1-1/2 inch is 1.711 in², which does not — that run needs 2 inch. Same conductors, same trench, one trade size apart.

Where NEC Article 352 allows PVC conduit — and where it does not

Rigid PVC conduit is covered by NEC Article 352. It is a complete raceway, but unlike steel it is not a ground path — 352.60 requires a wire-type equipment grounding conductor sized from Table 250.122 wherever equipment grounding is needed, and that conductor is part of your fill.

Permitted under 352.10

• Concealed in walls, floors and ceilings
• Locations subject to severe corrosive influences and in cinder fill
• Wet locations, including installations where walls are frequently washed
• Dry and damp locations not prohibited elsewhere in the Article
• Exposed where not subject to physical damage, if identified for the purpose
• Exposed where subject to physical damage, if identified for that use — this is the Schedule 80 case
• Underground, subject to the burial depths and requirements of 300.5 and 305.15

Not permitted under 352.12

• Hazardous (classified) locations, except where specifically permitted by other articles
• For the support of luminaires or other equipment, except conduit bodies no larger than the largest trade size of the conduit
• Where subject to physical damage, unless identified for that use
• Where the ambient temperature exceeds the conduit’s listed rating
• For conductors whose insulation temperature rating exceeds that of the conduit
• In theaters and similar locations, except as permitted by 518.4 and 520.5

Expansion fittings — the calculation nobody runs

NEC 352.44 requires an expansion fitting in a straight run once the expected length change reaches 0.25 inch. PVC has a coefficient of thermal expansion of roughly 3.38 × 10⁻⁵ in/in/°F, which works out to about 0.4 inch per 100 feet for every 10 °F of temperature change. A 100 foot exposed run seeing a 60 °F annual swing moves roughly 2.4 inches — ten times the threshold. Table 352.44 gives the exact figures; use it rather than eyeballing the run.

Support spacing comes from Table 352.30(B) and is tighter than steel conduit because PVC sags: 3 feet for 1/2 through 1 inch, 5 feet for 1-1/4 through 2 inch, 6 feet for 2-1/2 through 3 inch, 7 feet for 3-1/2 through 5 inch and 8 feet for 6 inch. Every run must also be secured within 3 feet of each box, cabinet or fitting.

PVC vs EMT vs IMC vs RMC — fill compared at 1 inch

Trade size is a naming convention, not a measurement. A 1 inch raceway is not 1 inch of anything in particular, and the usable area behind that label varies by more than 25% across raceway types:

Nine conductors separate IMC from Schedule 80 in a pipe both labelled 1 inch. That difference decides trench width, sweep radius and sometimes whether the feeder needs a larger pipe than the estimate allowed for.

For the method behind the published tables, see our walkthrough of sizing conduits and raceways with NEC Annex C, and NEC Chapter 9 Table 8 for the conductor properties that sit underneath it. The conductor itself is covered in our THHN/THWN-2 guide — and the wet rating matters here, because the inside of an underground PVC raceway is a wet location. When the raceway terminates, pull box and junction box sizing takes over from fill, and auxiliary gutters under Article 366 have their own 20% rule. If you are weighing a raceway against a cable assembly, compare with MC cable under Article 330.

Is PVC the right raceway for the run?

Working with PVC fill in the field

Frequently asked questions

How many 12 AWG THHN fit in 1 inch PVC?

Twenty-five in Schedule 40 and twenty in Schedule 80. The 40% allowance on a 1 inch Schedule 40 is 0.333 in² and a 12 AWG THHN is 0.0133 in², which gives 25. Schedule 80’s smaller bore gives 0.275 in², or 20 conductors.

Which NEC table is the PVC conduit fill chart?

Annex C Table C.10 for Rigid PVC Schedule 40 and HDPE, and Table C.9 for Rigid PVC Schedule 80. Table C.11 covers Type A rigid PVC and Table C.12 covers Type EB. The percentages behind all of them are in Chapter 9 Table 1.

Is conduit fill 40% or 53%?

Both, depending on how many conductors are in the raceway. Chapter 9 Table 1 allows 53% for a single conductor, 31% for exactly two, and 40% for three or more. Almost every circuit you pull falls under the 40% column.

Does the ground wire count toward conduit fill?

Yes. Chapter 9 Note 3 requires equipment grounding and bonding conductors to be included in the fill calculation at their actual dimensions, bare or insulated. They are excluded from the current-carrying conductor count used for derating under 310.15(C)(1), which is a different question.

Can a conduit nipple be filled more than 40%?

Yes. Chapter 9 Note 2 permits a nipple not exceeding 600 mm (24 in) in length between boxes, cabinets and similar enclosures to be filled to 60% of its total cross-sectional area, and the adjustment factors of 310.15(C)(1) do not apply to it.

What is the difference between Schedule 40 and Schedule 80 PVC conduit?

Wall thickness. Both share an outside diameter so they take the same fittings, but Schedule 80’s thicker wall gives it a physical-damage rating under 352.10(F) and takes 10–24% of the usable internal area away, depending on trade size. Schedule 80 has its own Annex C table.

Can I use the Annex C chart if my wires are different sizes?

No. Annex C is built on the assumption that every conductor in the raceway is the same size and insulation type. With mixed sizes you total the Chapter 9 Table 5 areas of every conductor and compare the sum against the Table 1 percentage of the Table 4 internal area.

Does PVC conduit need a separate ground wire?

Yes, wherever equipment grounding is required. PVC is nonmetallic and is not recognised as an equipment grounding conductor in 250.118, so NEC 352.60 requires a wire-type EGC sized from Table 250.122 to be run inside the raceway — and it counts toward your fill.

The bottom line

A PVC conduit fill chart is a shortcut, and like every shortcut it has conditions attached. It is valid when all the conductors are the same size, the same insulation, and the schedule on the chart matches the schedule in the trench. Break any one of those and the honest answer comes from Chapter 9 Tables 1, 4 and 5 with a calculator — which takes about ninety seconds and is what an inspector will ask you to show.

The two restraints worth memorising: Schedule 80 is never Schedule 40, and the ground wire counts toward fill but not toward derating. Get those two right and the rest of the chart takes care of itself. For what changed in the current code cycle, see our summary of the 2026 NEC updates, or compare editions in our NEC code book edition guide.