PVC Allowable Fill Area by Trade Size

Values represent allowable occupied cross-sectional area, not conduit diameter. The 40% column for Schedule 80 follows the NFPA-published values; other percentage columns are derived from the tabulated total and may differ from the printed table by 0.001 in². Verify against the NEC edition applicable to the project.

Maximum THHN/THWN-2 Conductors

How to Use the Schedule 40 Chart

Find the conductor size in the left column and read across to the trade size. For example, 1/2-in. Schedule 40 PVC holds 8 conductors of 12 AWG THHN/THWN-2, and 1-in. Schedule 40 holds 15 conductors of 10 AWG.

The counts apply only to same-size THHN/THWN/THWN-2 conductors in Schedule 40 PVC. They do not apply to other insulation types, mixed sizes, compact conductors or Schedule 80. Counts for one and two conductors follow their own limits and are not the 40% case.

Maximum THHN/THWN-2 Conductors

Counts are generally lower than in Schedule 40 because Schedule 80 has a thicker wall and less internal area at the same trade size. Annex C has a separate Schedule 80 table based on Chapter 9 Tables 1, 4 and 5, so do not estimate the difference from nominal pipe dimensions.

The NEC fill percentages are the same for both schedules. The difference is wall thickness, which changes the internal area.

For example, 1/2-in. Schedule 40 allows 0.114 in² at 40%, while 1/2-in. Schedule 80 allows 0.087 in². The rule is the same, and the smaller opening does the work.

Rigid PVC electrical conduit is covered by NEC Article 352. It is a nonmetallic raceway made in Schedule 40 and Schedule 80 wall thicknesses. Article 352 permits PVC in several concealed, corrosive, wet, outdoor and underground applications, and exposed use where permitted, subject to its requirements.

Electrical PVC conduit is not the same as plumbing PVC pipe. Conduit is made to electrical product standards such as UL 651 and NEMA TC 2, and its fill dimensions come from NEC Chapter 9 Table 4, not from plumbing pipe charts.

Chapter 9 Table 1 limits the total cross-sectional area of conductors and cables to a share of the conduit’s cross-sectional area.

One Conductor: 53%

A single conductor or cable may occupy 53% of the area.

Two Conductors: 31%

Exactly two conductors are limited to 31%.

Three or More Conductors: 40%

More than two conductors may occupy 40%. These percentages apply to the conduit cross-sectional area. Do not use 40% just because a chart is called a conduit fill chart.

Actual Fill Percentage

Maximum Allowable Area

Mixed-Conductor Formula

• N(i): quantity of each conductor
• A(i): area of that insulated conductor (in²)
• F: applicable fill fraction, written as a decimal

Use square inches consistently.

1. Determine Schedule 40 or Schedule 80.
2. Determine the conduit trade size.
3. Count conductors and cables.
4. Identify each conductor size.
5. Identify insulation and construction.
6. Obtain conductor areas from Table 5.
7. Include grounding and bonding conductors.
8. Add the occupied areas.
9. Determine the applicable fill percentage.
10. Compare occupied area with permitted area.
11. Then separately verify ampacity and installation requirements.

Three 12 AWG Conductors

Mixed Conductor Sizes

The 6 AWG and 4 AWG counts of 1 are single-conductor cases, so they follow the 53% limit and not 40%.

The 40% areas are 0.203 in² for Schedule 40 and 0.164 in² for Schedule 80.

The 40% areas are 0.333 in² for Schedule 40 and 0.275 in² for Schedule 80, a practical capacity difference of about 17%.

Larger sizes share one table. Counts are shown as Schedule 40 / Schedule 80 for same-size THHN/THWN-2 conductors.

AWG alone does not determine conduit fill. Two conductors of the same size can have different overall dimensions because of insulation and construction. See the Wire Gauge Chart for AWG dimensions.

Do not transfer THHN counts to XHHW or XHHW-2, RHH/RHW or other constructions, or to compact conductors, which use Table 5A.

Equipment Grounding Conductor

Include its actual area. Chapter 9 Table 1 Note 3 requires installed equipment grounding and bonding conductors to be included in the fill calculation using their actual dimensions.

Neutral Conductor

A neutral physically occupies conduit space, so it contributes to fill.

Spare Conductor

A spare occupies area and counts.

Conduit-fill counting and current-carrying-conductor counting for ampacity are different questions. For example, adding a 12 AWG THHN ground to three 12 AWG conductors in 1/2-in. Schedule 40 PVC gives 4 × 0.0133 = 0.0532 in², under the 0.114 in² limit.

Chapter 9 Table 1 Note 4 allows a conduit or tubing nipple not longer than 24 in. (600 mm) between boxes, cabinets and similar enclosures to be filled to 60% of its cross-sectional area.

Passing the conduit-fill calculation does not establish ampacity compliance.

The maximum legal fill is not always the best practical design. Pull length, the number of bends, conductor diameter, pulling tension, sidewall pressure and jamming all matter. NFPA material notes the potential for jamming, and Southwire calculates fill, pulling tension, sidewall pressure and jam probability separately.

Do not reduce the decision to capacity. Schedule 80 PVC is identified for locations subject to physical damage, while Schedule 40 is not identified for that use. Schedule 40’s larger internal area does not mean it can simply replace Schedule 80 wherever more capacity is desirable.

Check Article 352 and the AHJ for where each schedule is permitted or required, and size the raceway for the schedule you must use.

Only the points that affect selecting and filling conduit are covered here. They include underground installation, wet locations, physical damage, bends, pull points, expansion and thermal movement, support, listed fittings and solvent-cemented joints. CANTEX’s installation documentation shows belled-end conduit being prepared and solvent-cemented in underground work.

This is not a complete PVC installation guide, so follow the NEC, the manufacturer’s instructions and local rules.

The NEC percentages can be the same while the available internal area differs. Equal trade sizes of EMT, Schedule 40 PVC and Schedule 80 PVC should not be assumed to hold the same number of conductors. For 3/4-in. raceways, Table 4 lists:

The EMT Conduit Fill Chart has the EMT dimensions and counts, and the Conduit Fill Chart compares all the raceway types.

Fill compliance does not establish ampacity or complete NEC compliance, so treat this as a sequence and not a single lookup.

The checker uses THHN/THWN/THWN-2 areas and a direct area comparison. Include grounding conductors, and use it for practice, not permit approval.

Limitations