Conduit Fill Chart: Complete NEC Wire Fill Table Guide

Every conduit fill calculation starts with the same question: how many wires can you legally pull through this pipe? The answer lives in NEC Chapter 9, specifically Tables 1, 4, and 5. This conduit fill chart puts those NEC wire fill tables in one place so you can size your raceway correctly the first time.

Below you'll find the conduit fill percentage rules, complete conduit fill tables for EMT, IMC, rigid metal (RMC), and PVC conduit, plus a THHN wire fill chart that tells you exactly how many conductors of each gauge fit in each trade size. If you want instant results instead of manual lookups, our conduit fill calculator does the math for you.

NEC Conduit Fill Percentage Rules (Table 1)

Before you touch a conduit fill table, you need to know the fill limits. NEC Chapter 9, Table 1 sets the maximum percentage of a conduit's internal area that conductors can occupy. The percentages change based on the number of conductors.

The 40% conduit fill rule is the one you'll use most often. Most circuits run a hot, neutral, and equipment grounding conductor at minimum, which puts you at three or more conductors. That 40% limit accounts for heat dissipation (wires packed too tightly overheat) and practical pulling (you need room to snake conductors through without damaging insulation).

EMT Conduit Fill Chart (Table 4)

Electrical metallic tubing (EMT) is the most common raceway on commercial and residential projects. The table below shows the internal area and allowable fill areas for each EMT trade size, pulled directly from NEC Chapter 9, Table 4.

To use this table: look up your conduit trade size, then check the column that matches your conductor count. The value in that cell is the maximum total cross-sectional area of all conductors combined. Compare that against the sum of your individual conductor areas from Table 5 (covered below).

Rigid Metal Conduit (RMC) Fill Chart

Rigid metal conduit has thicker walls than EMT, which means a slightly smaller internal diameter for the same trade size. Here are the fill areas for RMC.

IMC Conduit Fill Chart

Intermediate metal conduit (IMC) splits the difference between EMT and rigid. It's lighter than RMC but stronger than EMT. Its internal dimensions fall between the two.

PVC Conduit Fill Chart (Schedule 40)

PVC Schedule 40 is common in underground and exposed outdoor installations. Its internal dimensions differ from metal conduit types, so you need the right table.

THHN Wire Fill Chart (Annex C)

This is the table most electricians actually want: the maximum number of THHN/THWN-2 conductors allowed in each conduit size at the standard 40% fill. THHN is the most common building wire insulation type, and these counts come from NEC Annex C. No math required.

THHN in EMT

THHN in Rigid Metal Conduit (RMC)

THHN in PVC Schedule 40

Conductor Cross-Sectional Areas (Table 5)

When you're working with mixed wire sizes, you can't use the Annex C tables. Instead, you need the cross-sectional area of each individual conductor from NEC Table 5. Add them up, then compare the total against the appropriate column in Table 4. Here are the areas for the most common insulation types.

Key detail: THHN has a thinner insulation layer than THW, which is why its cross-sectional area is smaller for the same gauge. This means you can fit more THHN conductors in a given conduit than THW. It's one reason THHN is the go-to wire for commercial work.

How to Calculate Conduit Fill (Step by Step)

Here's the process for sizing conduit when you're pulling wire. You can do this by hand with the tables above or let the conduit fill calculator handle it instantly.

Step 1: Count Your Conductors

List every conductor going into the raceway. Include hot conductors, neutrals, equipment grounding conductors, travelers, and any other wires. Remember: the grounding conductor counts toward fill.

Step 2: Determine Your Fill Percentage

Use NEC Table 1 (see above). One conductor = 53%. Two conductors = 31%. Three or more = 40%. Nipples 24" or shorter = 60%.

Step 3: Find Conductor Areas

Look up each conductor's cross-sectional area in NEC Table 5. If all conductors are the same gauge and insulation type, you can skip to the Annex C tables and get a direct wire count. For mixed sizes, add up the individual areas.

Step 4: Select Conduit Size

Find the conduit type you're using in Table 4. Scan down the appropriate fill percentage column until you find a value that equals or exceeds your total conductor area. That's your minimum conduit size.

Worked Examples

Example 1: Simple Circuit in EMT

You need to run three 12 AWG THHN conductors (hot, neutral, ground) through EMT. How small can your conduit be?

• Conductor count: 3 (use 40% fill)
• Area per conductor: 12 AWG THHN = 0.0133 sq in (from Table 5)
• Total area: 3 x 0.0133 = 0.0399 sq in
• EMT Table 4, 40% column: 1/2" EMT allows 0.1220 sq in
• Result: 1/2" EMT works. You have plenty of room.

Quick check: the THHN in EMT chart shows 9 conductors of 12 AWG fit in 1/2" EMT. You only need 3. Confirmed.

Example 2: Mixed Wire Sizes

You're pulling through rigid conduit: four 10 AWG THHN, two 6 AWG THHN, and one 10 AWG THHN ground. What size RMC do you need?

• Conductor count: 7 (use 40% fill)
• 10 AWG THHN area: 5 x 0.0211 = 0.1055 sq in
• 6 AWG THHN area: 2 x 0.0507 = 0.1014 sq in
• Total area: 0.1055 + 0.1014 = 0.2069 sq in
• RMC Table 4, 40% column: 3/4" RMC allows 0.2200 sq in. That's more than 0.2069.
• Result: 3/4" RMC is your minimum. It's tight though. Consider 1" RMC to make the pull easier.

Example 3: Using the Nipple Exception

You have an 18-inch conduit nipple between two boxes. Can you pull six 10 AWG THHN conductors through 1/2" EMT?

• It's a nipple (under 24"): Use 60% fill
• Total area: 6 x 0.0211 = 0.1266 sq in
• 1/2" EMT total area: 0.3040 sq in
• 60% of total area: 0.3040 x 0.60 = 0.1824 sq in
• Result: 0.1266 is less than 0.1824. Yes, it's code compliant.

Common Conduit Fill Mistakes

Inspectors catch these on a regular basis. Avoid them.

• Forgetting the ground wire. Equipment grounding conductors count toward fill and toward conductor count. A "two-wire" circuit actually has three conductors.
• Using the wrong conduit table. EMT, IMC, RMC, and PVC all have different internal areas. Don't use the EMT table when you're pulling through rigid.
• Ignoring insulation type. THW insulation is thicker than THHN. The same gauge wire has a larger cross-sectional area with THW insulation. Using THHN numbers for THW wire will undersize your conduit.
• Mixing up trade size with actual diameter. A 1/2" EMT has an internal diameter of 0.622 inches, not 0.5 inches. Trade sizes are nominal, not actual dimensions.
• Applying 40% to nipples. Nipples under 24 inches get 60% fill. Using 40% is conservative but may cause you to upsize unnecessarily.
• Using Annex C for mixed sizes. Annex C tables only work when every conductor in the raceway is the same size and insulation type. For mixed sizes, you must calculate from Tables 4 and 5.

Understanding NEC Chapter 9

NEC Chapter 9 contains the notes and tables that govern conduit fill calculations. The tables work together as a system. Here's how they connect.

The critical notes at the beginning of Chapter 9 include the nipple exception (Note 4) and the requirement that all conduit areas are based on the dimensions published in applicable product standards. This is why conduit manufacturers' specifications should match what you see in Table 4.

Using the Conduit Fill Calculator

Looking up tables and doing arithmetic by hand works, but it's slow and error-prone on a busy job site. The conduit fill calculator in the Conduit Bending app handles all of this automatically.

Select your conduit type and trade size, add your conductors (mix sizes freely), and the calculator returns the fill percentage, remaining area, and a pass/fail result against the NEC limit. It uses the same NEC Chapter 9 data shown in the tables above. You can also adjust for nipple runs to apply the 60% limit.

Download Conduit Bending free on the App Store to run conduit fill calculations in the field, along with offset bends, saddles, 90s, and every other conduit math problem you'll run into.

Related Guides

• EMT vs Rigid vs IMC Conduit breaks down wall thickness, fittings, and NEC articles for each conduit type. Different types have different internal areas, which directly affects fill capacity.
• Conduit Bending Formulas & Deduct Charts covers the deduct, multiplier, and shrink values you'll need once the conduit is sized.
• How to Bend Conduit is the full beginner's guide to every bend type, from 90s to rolling offsets.

Conduit Bending App 16 bend types, bender library, fraction calculator. Free on iOS.