NEC Conduit Fill Percentage Chart

These percentages are maximum occupied cross-sectional areas, not percentages of conduit diameter and not universal wire-count limits.

Common EMT and THHN Wire Counts

Do not use this table for different insulation types, mixed conductor sizes, compact conductors or another raceway type. Counts of one and two conductors reflect their own fill limits and are not recomputed with 40%. Values follow the NEC Annex C method, including the Chapter 9 Note 7 rounding rule for same-size conductors. The 6 AWG entry in 1/2-in. EMT (2) depends on that rounding, because two 6 AWG conductors exceed 31% by strict area, and some charts list 1.

Code-Edition Note

Conduit fill is the share of a raceway’s internal cross-sectional area that installed conductors and cables occupy.

Occupied Conductor Area

Raceway fill uses the overall insulated conductor area. The copper or aluminum metal area alone is not what you enter for insulated conductors.

Raceway Internal Area

Use the actual tabulated internal area for the raceway type, not a value guessed from the trade size.

One Conductor: 53%

A single conductor or cable may occupy up to 53% of the raceway area. It cannot wedge against another conductor, so Table 1 allows a higher percentage.

Two Conductors: 31%

Exactly two conductors are limited to 31%. Do not assume they receive 40%, because two round conductors pack less efficiently in a round raceway and can jam.

Three or More Conductors: 40%

More than two conductors may fill 40% of the area. It is the most familiar field value, and it is why many people mistakenly quote 40% for all conduit.

These percentages depend on the number of conductors or cables, not on their ampacity.

Chapter 9 Table 1 Note 4 allows a conduit or tubing nipple not exceeding 24 in. (600 mm) that is installed between boxes, cabinets and similar enclosures to be filled to 60% of its total cross-sectional area. The note also addresses ampacity adjustment for this condition, so read it in your adopted edition.

Follow the same steps for any raceway.

Identify Raceway

Choose the type (EMT, IMC, RMC, PVC Schedule 40 or 80, FMC, LFMC, LFNC or ENT) and its trade size.

Identify Conductors

Record the quantity, AWG or kcmil size, insulation and construction, whether the conductor is compact, any grounding or bonding conductors, and the outside diameter of any cable.

Calculate Occupied Area

Take each area from Table 5 (or Table 5A for compact conductors, or actual dimensions where the tables do not apply) and add them up.

Compare With Allowable Area

The conductors fit when A(conductors) is not more than A(allowed).

Use either form, with F written as a decimal.

• A(c): combined conductor and cable area (in²)
• A(r): total internal raceway area (in²)
• F: 0.53, 0.31 or 0.40 (or 0.60 for a qualifying nipple)

For example, 40% is written as 0.40 in calculations.

Three 12 AWG THHN in 1/2-in. EMT

Mixed Conductor Sizes

Annex C is a shortcut for uniform conductors. NFPA’s own training directs users to Annex C when all conductors are one size and to Chapter 9 Tables 1, 4 and 5 for multiple sizes.

Same-Size Conductors

Annex C works well when the raceway type, conductor size and insulation or construction are all the same. Chapter 9 Note 7 allows the next higher whole number when the calculation leaves a decimal of 0.8 or more for same-size conductors.

Mixed-Size Conductors

Calculate instead when AWG or kcmil sizes, insulation types, cables or special constructions are mixed.

EMT is widely used, and its capacity comes from its tabulated internal area, not its trade size. The Annex C-derived EMT counts for common THHN and THWN sizes are in the quick-reference table above. For an EMT-only reference with larger sizes and mixed-conductor examples, see the EMT Conduit Fill Chart.

Schedule 40 PVC has its own Table 4 dimensions and its own Annex C tables, so never copy EMT counts into PVC. For a PVC-focused reference, see the PVC Conduit Fill Chart.

Schedule 80 has thicker walls, so the internal area is smaller at the same trade size. The difference depends on the trade size and the conductors, so avoid a blanket claim about how many fewer wires it holds.

Rigid metal conduit and intermediate metal conduit are separate raceways with their own areas. Do not infer an RMC or IMC result from EMT.

Flexible raceways use their own Table 4 areas. Do not use EMT dimensions, and flexible construction does not remove fill requirements.

FMC

Flexible metal conduit has no jacket, and its internal area differs from the other raceways across most trade sizes.

LFMC

Liquidtight flexible metal conduit adds a jacket over a metal core. Use the LFMC values, not FMC or EMT.

LFNC

Liquidtight flexible nonmetallic conduit is tabulated by construction type. Type A and Type B have different internal areas, so confirm which one your product is. Do not merge all liquidtight raceways into one chart.

Electrical nonmetallic tubing (Article 362) has its own Table 4 dimensions and its own Annex C table. A 2020 NEC-based published reference shows these same-size THHN counts, which are historical examples unless you confirm them against the edition you use:

Trade size is a nominal name. The table below compares 3/4-in. raceways.

AWG names the conductor size. Raceway fill needs the overall conductor dimensions, which depend on insulation and whether the conductor is compact. For AWG dimensions and conversions, use the Wire Gauge Chart, which owns that reference, and come back here for raceway area.

• AWG: identifies the metal conductor size.
• Insulation type: changes overall diameter and area.
• Compact conductors: use their own Table 5A data.

Do not treat 12 AWG as 0.0133 in² for every insulated conductor. That value is for THHN, THWN and THWN-2 only.

Compact conductors are compressed so the voids between strands are virtually eliminated, which changes their dimensions. NFPA’s own training tells users to choose the correct standard or compact table. Use Table 5A (and the compact-conductor Annex C counterpart) instead of the standard THHN values, because a standard THHN count cannot automatically be used for compact conductors. Most aluminum building wire is compact stranded.

Installed equipment grounding and bonding conductors count toward raceway fill. Chapter 9 Table 1 Note 3 requires their actual dimensions to be used.

Insulated Equipment Ground

Use the applicable insulated dimensions, such as the Table 5 area for its insulation type.

Bare Equipment Ground

Use the actual applicable dimensions. Where bare conductors are permitted, Table 8 gives them.

Multiple Grounding Conductors

Count every installed grounding and bonding conductor for fill. Sizing those conductors follows separate rules.

Chapter 9 notes direct users to actual dimensions for conductors and cables not included in the tabulated conductor data. For a round cable:

where A is the cable cross-sectional area and D is the actual cable outside diameter. A multiconductor cable is treated as a single conductor when calculating percentage fill, and for an elliptical cable the calculation uses the major diameter of the ellipse as the circle diameter. Follow your adopted NEC’s exact wording for non-round cables, and do not invent an equivalent-diameter rule. Not every multiconductor cable is treated identically under every NEC provision.

There is no single answer. For 1/2-in. EMT with same-size THHN or THWN conductors, the counts are 12 (14 AWG), 9 (12 AWG), 5 (10 AWG), 3 (8 AWG) and 2 (6 AWG).

Conditions: same-size THHN or THWN conductors with no separate grounding conductor. Add a ground and the circuit count drops. Do not treat these as universal counts for the trade size.

For 3/4-in. EMT with same-size THHN or THWN, the counts are 22 (14 AWG), 16 (12 AWG), 10 (10 AWG), 6 (8 AWG) and 4 (6 AWG).

Conditions: same-size THHN or THWN conductors with no separate grounding conductor. Add a ground and the circuit count drops. Do not treat these as universal counts for the trade size.

For 1-in. EMT with same-size THHN or THWN, the counts are 35 (14 AWG), 26 (12 AWG), 16 (10 AWG), 9 (8 AWG), 7 (6 AWG) and 4 (4 AWG).

Conditions: same-size THHN or THWN conductors with no separate grounding conductor. Add a ground and the circuit count drops. Do not treat these as universal counts for the trade size.

Larger feeders increasingly need an exact area calculation, and memory-based rules do not hold up for them.

Conduit fill asks how much physical raceway area is occupied. Ampacity adjustment asks how many current-carrying conductors share the installation and what that does to allowable ampacity. A raceway can pass the fill calculation and still need adjustment.

Conductor ampacity, correction and adjustment factors, terminal limitations, voltage drop, pulling tension and bends are separate checks. This page does not replace an ampacity chart.

Meeting the maximum fill percentage does not guarantee an easy or safe pull. Consider the following:

• Number of bends and pull length
• Conductor or cable outside diameter and raceway inside diameter
• Pulling tension and sidewall pressure
• Jamming and lubrication
• Manufacturer pulling limits

Professional tools such as the Southwire conduit-fill calculator report fill and jam probability separately, which shows that they are related but distinct checks. Do not use a universal safe jam ratio without a suitable technical source.

Fill percentages do not authorize unlimited bends or remove pulling considerations. Straight runs, 90-degree bends, multiple bends and pull points all change how hard a pull is. A future Conduit Bending Chart would cover bend geometry, so this page treats bends conceptually.

1. List all conductors.
2. Identify the exact insulation and construction of each.
3. Include grounding and bonding conductors.
4. Determine the occupied area.
5. Determine the applicable fill percentage.
6. Compare with each candidate raceway.
7. Select the smallest code-compliant candidate.
8. Check ampacity separately.
9. Check pulling and bending practicality.
10. Verify the adopted code and AHJ requirements.

The smallest legal raceway and the best practical raceway are not always the same. The mixed-conductor example above needed 2-in. EMT to satisfy fill.

The checker uses THHN/THWN/THWN-2 areas from Table 5 and a direct area comparison. Annex C may allow one more same-size conductor under the Note 7 rounding rule. Use it for practice, not for permit approval.

NEC maximum fill is a limit, not necessarily a design target. A designer or contractor may choose a larger raceway for easier pulling, long runs, multiple bends, future circuits, maintenance or cable replacement. Do not assume a mandatory design fill such as 25% or 30% unless the project specification sets one.

Limitations

The tables reproduce a focused subset of NEC Chapter 9 data as published in recent editions, and some counts are calculated from those tables. Confirm every value against the edition your AHJ has adopted. See the Construction Charts hub for related references and the Engineering Calculators for calculation tools.