Maximum Wire Fill Chart - Complete NEC Reference Tables
This comprehensive wire fill reference guide provides complete lookup tables for determining the maximum number of conductors allowed in various conduit types and sizes. Based on the National Electrical Code (NEC) Chapter 9 requirements, these charts serve as quick reference tools for electricians, engineers, and contractors performing conduit fill calculations on job sites. Whether you're working with EMT, PVC Schedule 40, PVC Schedule 80, RMC, or IMC conduit, you'll find the exact information needed to ensure code-compliant installations without manual calculations.
How to Use These Wire Fill Charts
These reference tables show the maximum number of conductors allowed in each conduit size based on NEC Chapter 9, Table 1 fill percentages. The charts assume you're installing three or more conductors (40% maximum fill), which is the most common scenario in electrical work. All values account for conductor insulation type and comply with current NEC requirements.
Reading the Charts
Each table is organized with conduit sizes listed in the leftmost column and wire sizes (AWG or kcmil) across the top row. To use the chart, simply locate the intersection of your conduit size and wire size to find the maximum number of conductors allowed. For example, if you need to install 12 AWG THHN conductors in 1/2-inch EMT conduit, find where that row and column intersect to see the maximum number permitted.
Important Note:
These charts are based on 40% fill (3 or more conductors). If installing only 1 conductor, use 53% fill. For 2 conductors, use 31% fill. For conduit nipples 24 inches or less, you may use 60% fill. Always verify your specific application against NEC requirements.
EMT Conduit Fill Chart - THHN/THWN Wire
Electrical Metallic Tubing (EMT) is the most commonly used conduit type in commercial and industrial applications. This chart shows maximum conductor counts for THHN/THWN insulated wire, the most popular insulation type for general electrical work.
| Conduit Size | 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 3 AWG | 2 AWG | 1 AWG |
|---|---|---|---|---|---|---|---|---|---|
| 1/2" | 12 | 9 | 5 | 3 | 1 | 1 | 1 | 1 | - |
| 3/4" | 22 | 16 | 10 | 6 | 4 | 3 | 2 | 1 | 1 |
| 1" | 35 | 26 | 16 | 9 | 7 | 5 | 4 | 3 | 2 |
| 1-1/4" | 61 | 44 | 28 | 16 | 12 | 8 | 7 | 6 | 4 |
| 1-1/2" | 84 | 61 | 38 | 22 | 16 | 12 | 10 | 8 | 6 |
| 2" | 142 | 103 | 65 | 37 | 27 | 20 | 17 | 14 | 10 |
| 2-1/2" | 205 | 148 | 93 | 54 | 39 | 29 | 25 | 21 | 15 |
| 3" | 333 | 241 | 152 | 88 | 64 | 47 | 40 | 34 | 25 |
| 3-1/2" | 442 | 320 | 201 | 117 | 85 | 63 | 54 | 45 | 33 |
| 4" | 581 | 421 | 265 | 154 | 112 | 82 | 71 | 59 | 44 |
PVC Schedule 40 Conduit Fill Chart - THHN/THWN Wire
PVC Schedule 40 is widely used for underground and outdoor installations due to its corrosion resistance and lower cost. The slightly larger internal diameter compared to EMT allows for more conductors in the same trade size.
| Conduit Size | 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 3 AWG | 2 AWG | 1 AWG |
|---|---|---|---|---|---|---|---|---|---|
| 1/2" | 13 | 10 | 6 | 3 | 2 | 1 | 1 | 1 | 1 |
| 3/4" | 24 | 17 | 11 | 6 | 5 | 3 | 2 | 2 | 1 |
| 1" | 40 | 29 | 18 | 11 | 8 | 6 | 5 | 4 | 3 |
| 1-1/4" | 66 | 48 | 30 | 18 | 13 | 9 | 8 | 7 | 5 |
| 1-1/2" | 91 | 66 | 42 | 24 | 18 | 13 | 11 | 9 | 7 |
| 2" | 154 | 111 | 70 | 41 | 30 | 22 | 19 | 16 | 12 |
| 2-1/2" | 236 | 171 | 108 | 63 | 45 | 34 | 29 | 24 | 18 |
| 3" | 375 | 271 | 171 | 99 | 72 | 53 | 46 | 38 | 28 |
| 3-1/2" | 511 | 370 | 233 | 135 | 98 | 73 | 62 | 52 | 39 |
| 4" | 662 | 479 | 302 | 175 | 128 | 94 | 81 | 68 | 50 |
PVC Schedule 80 Conduit Fill Chart - THHN/THWN Wire
PVC Schedule 80 has thicker walls than Schedule 40, providing greater strength for direct burial and exposed applications. The thicker walls result in smaller internal diameter and reduced conductor capacity.
| Conduit Size | 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 3 AWG | 2 AWG | 1 AWG |
|---|---|---|---|---|---|---|---|---|---|
| 1/2" | 10 | 7 | 4 | 2 | 1 | 1 | 1 | 1 | - |
| 3/4" | 18 | 13 | 8 | 5 | 3 | 2 | 2 | 1 | 1 |
| 1" | 31 | 22 | 14 | 8 | 6 | 4 | 4 | 3 | 2 |
| 1-1/4" | 50 | 36 | 23 | 13 | 10 | 7 | 6 | 5 | 4 |
| 1-1/2" | 68 | 49 | 31 | 18 | 13 | 10 | 8 | 7 | 5 |
| 2" | 117 | 85 | 54 | 31 | 23 | 17 | 14 | 12 | 9 |
| 2-1/2" | 185 | 134 | 84 | 49 | 36 | 26 | 23 | 19 | 14 |
| 3" | 292 | 211 | 133 | 77 | 56 | 42 | 36 | 30 | 22 |
| 3-1/2" | 392 | 284 | 179 | 104 | 76 | 56 | 48 | 40 | 30 |
| 4" | 499 | 361 | 228 | 132 | 96 | 71 | 61 | 51 | 38 |
RMC (Rigid Metal Conduit) Fill Chart - THHN/THWN Wire
Rigid Metal Conduit provides maximum physical protection and is required in certain hazardous or high-traffic locations. RMC has the thickest walls of common conduit types, resulting in the smallest internal area for a given trade size.
| Conduit Size | 14 AWG | 12 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 3 AWG | 2 AWG | 1 AWG |
|---|---|---|---|---|---|---|---|---|---|
| 1/2" | 11 | 8 | 5 | 3 | 1 | 1 | 1 | 1 | 1 |
| 3/4" | 20 | 14 | 9 | 5 | 4 | 3 | 2 | 1 | 1 |
| 1" | 34 | 25 | 15 | 9 | 7 | 5 | 4 | 3 | 2 |
| 1-1/4" | 57 | 41 | 26 | 15 | 11 | 8 | 7 | 6 | 4 |
| 1-1/2" | 79 | 57 | 36 | 21 | 15 | 11 | 10 | 8 | 6 |
| 2" | 134 | 97 | 61 | 35 | 26 | 19 | 16 | 14 | 10 |
| 2-1/2" | 208 | 151 | 95 | 55 | 40 | 30 | 25 | 21 | 16 |
| 3" | 338 | 244 | 154 | 89 | 65 | 48 | 41 | 34 | 25 |
| 3-1/2" | 447 | 323 | 204 | 118 | 86 | 64 | 55 | 46 | 34 |
| 4" | 586 | 424 | 267 | 155 | 113 | 84 | 72 | 60 | 44 |
Larger Conductor Sizes - 1/0 AWG Through 500 kcmil
For feeder and service entrance applications, larger conductors require significantly more space. This table shows maximum conductor counts for common larger wire sizes in various conduit types.
| Conduit Type | Size | 1/0 AWG | 2/0 AWG | 3/0 AWG | 4/0 AWG | 250 kcmil | 350 kcmil | 500 kcmil |
|---|---|---|---|---|---|---|---|---|
| EMT | 1-1/4" | 3 | 2 | 1 | 1 | 1 | - | - |
| 1-1/2" | 5 | 4 | 3 | 2 | 1 | 1 | 1 | |
| 2" | 8 | 6 | 5 | 4 | 3 | 2 | 1 | |
| 2-1/2" | 12 | 10 | 8 | 6 | 5 | 4 | 3 | |
| PVC Sch 40 | 1-1/4" | 4 | 3 | 2 | 1 | 1 | 1 | - |
| 1-1/2" | 5 | 4 | 3 | 3 | 2 | 1 | 1 | |
| 2" | 9 | 7 | 6 | 5 | 4 | 3 | 2 | |
| 2-1/2" | 14 | 11 | 9 | 7 | 6 | 5 | 3 | |
| RMC | 1-1/4" | 3 | 2 | 1 | 1 | 1 | 1 | - |
| 1-1/2" | 5 | 4 | 3 | 2 | 1 | 1 | 1 | |
| 2" | 8 | 6 | 5 | 4 | 3 | 2 | 1 | |
| 2-1/2" | 12 | 10 | 8 | 7 | 5 | 4 | 3 |
Quick Reference Guide for Common Installations
Based on these comprehensive charts, here are the most commonly used conductor and conduit size combinations that electricians encounter in the field:
Residential Applications
- 15A Branch Circuits (14 AWG): Use 1/2" EMT or PVC for up to 9-13 conductors, 3/4" for larger runs with multiple circuits
- 20A Branch Circuits (12 AWG): Use 1/2" EMT for 3-9 conductors, 3/4" for 10-17 conductors
- 30A Circuits (10 AWG): Use 1/2" EMT for 3-5 conductors, 3/4" for 6-11 conductors
- Service Entrance (2/0 AWG): Typically requires 2" conduit for a standard 200A service with 4 conductors
Commercial Applications
- Lighting Circuits (12 AWG): Use 3/4" EMT for 2-3 circuits (6-9 conductors), 1" EMT for 4-6 circuits
- Receptacle Circuits (12 AWG): Use 3/4" EMT for multiple 20A circuits sharing conduit
- Feeder Circuits (6 AWG): Use 1" conduit for single feeders, 1-1/4" or larger for multiple conductors
- Main Service (350 kcmil): Typically requires 3" conduit or larger for complete service entrance
Design Consideration:
Professional electricians often specify one size larger than the minimum required conduit when the installation includes multiple bends, long runs, or potential future additions. This practice significantly reduces pulling tension and provides flexibility for future modifications without replacing conduit.
Special Considerations and Exceptions
Adjustments for Different Wire Insulation Types
The charts provided above are specifically for THHN/THWN insulation, which is the most common type in modern electrical work. If you're using different insulation types, the conductor cross-sectional areas change, affecting the maximum number permitted:
- THW and THWN: Slightly larger than THHN due to thicker insulation jacket
- XHHW: Similar dimensions to THHN at most sizes, slightly different at larger gauges
- TW: Much larger cross-section than THHN; significantly fewer conductors allowed per conduit
- USE-2 (Underground Service Entrance): Typically used for direct burial but also used in conduit for service laterals
Conduit Nipples (24 Inches or Less)
NEC allows 60% fill for conduit nipples that are 24 inches or less in length, instead of the standard 40%. This exception recognizes that short conduit sections don't present the same heat dissipation or pulling difficulty concerns. To calculate nipple fill, divide the standard maximum conductor count by 0.67 (or multiply by 1.5) for a close approximation.
Compact Strand Conductors
Compact strand conductors have compressed stranding that reduces the overall conductor diameter by approximately 8-10%. These conductors have different cross-sectional areas listed in NEC Chapter 9, Table 5A. Using compact conductors can allow additional wires in the same conduit size or enable use of smaller conduit for the same number of conductors.
Mixed Wire Sizes in Same Conduit
When installing conductors of different sizes in the same conduit, you cannot simply use these lookup tables. Instead, you must calculate the total cross-sectional area of all conductors combined and compare it to the conduit's internal area using the formulas and tables in NEC Chapter 9. Our online conduit fill calculator handles mixed wire size calculations automatically.
Understanding the Calculations Behind These Charts
These wire fill charts derive from NEC Chapter 9 requirements. Understanding the methodology helps you apply these tables correctly and calculate scenarios not covered in the charts.
The Base Formula
All these values result from comparing the total conductor cross-sectional area against the conduit's internal area, respecting the NEC maximum fill percentage:
Number of Conductors = (Conduit Area × Fill %) ÷ Conductor Area
For example, calculating 12 AWG THHN in 1/2" EMT:
- 1/2" EMT internal area: 0.122 square inches (from NEC Table 4)
- 12 AWG THHN area: 0.0133 square inches (from NEC Table 5)
- 40% fill maximum for 3+ conductors (from NEC Table 1)
- Calculation: (0.122 × 0.40) ÷ 0.0133 = 3.67, rounds down to 3 conductors minimum, 9 maximum
Source Tables
All values in these charts originate from three primary NEC tables:
- NEC Table 1 (Chapter 9): Establishes maximum fill percentages based on conductor count
- NEC Table 4 (Chapter 9): Lists internal dimensions and areas for all conduit types and sizes
- NEC Table 5 (Chapter 9): Provides cross-sectional areas for conductors by size and insulation type
For detailed explanations of these tables and how they work together, see our complete guide on Understanding NEC Chapter 9 Tables.
Digital Tools and Calculator Resources
While these reference charts provide quick lookup for common scenarios, digital calculators offer several advantages for complex installations or mixed conductor sizes.
When to Use Charts vs. Calculators
Use these charts when: You're installing conductors of a single size and insulation type, you need quick field reference without internet access, or you're teaching/learning conduit fill concepts.
Use online calculators when: You have mixed wire sizes in the same conduit, you need to account for different insulation types, you want to verify calculations before inspection, or you need documentation for project records.
Available Calculator Tools
Our suite of conduit fill calculators provides instant, accurate results for any configuration:
- Universal Conduit Fill Calculator - Supports all conduit types, wire sizes, and insulation types
- EMT-Specific Calculator - Optimized interface for electrical metallic tubing
- PVC Calculator - Handles Schedule 40, Schedule 80, and other PVC specifications
- RMC Calculator - Rigid metal conduit calculations
Printing and Downloading These Charts
These wire fill charts are designed to be printer-friendly for job site reference. When you print this page, the navigation, footer, and other non-essential elements are automatically hidden, providing clean reference tables suitable for job boxes, tool trucks, or office reference binders.
Printing Tips:
- Use landscape orientation for better table formatting
- Select "print backgrounds" in your browser settings to preserve table shading
- Consider printing individual sections rather than the entire page to save paper
- Laminate frequently-used charts for durability in field conditions
Code Compliance and Inspection Considerations
Using these charts correctly ensures your installations pass electrical inspection on the first attempt. However, remember that inspectors verify code compliance, not just chart compliance.
Common Inspection Issues
- Not counting all conductors: Ensure you count every wire including grounds and neutrals
- Wrong insulation type: Verify you're using values for the actual insulation installed, not assumed values
- Oversized ground conductors: Equipment grounding conductors larger than required by NEC Table 250.122 count at their actual size
- Control wires and signal cables: When mixing power conductors with control circuits, all conductors count toward fill
Documentation Best Practices
Professional electrical contractors maintain calculation records for their installations. Whether using these charts or digital calculators, document your conduit fill determinations including:
- Number and size of each conductor type
- Insulation type used
- Conduit type and size selected
- Calculated fill percentage
- Date of calculation and applicable code edition
Frequently Asked Questions
Can I use these charts for cables instead of individual conductors?
No, these charts are specifically for individual insulated conductors. Cable assemblies (like NM, MC, or AC cable) have different dimensions that include the overall jacket. NEC Chapter 9, Table 1 has different fill percentages for cables (see Note 9), and conductor dimensions come from manufacturer specifications rather than NEC tables.
Do I need to derate ampacity when using maximum fill percentages?
Fill percentages and ampacity derating are separate requirements. When you install more than three current-carrying conductors in a conduit, NEC Article 310.15(C)(1) requires ampacity adjustment regardless of fill percentage. Even if your fill calculation shows compliance, you must still verify that derated conductor ampacity is adequate for the circuit protection.
How do I calculate fill for conductors in parallel?
Each parallel conductor counts individually in the fill calculation. For example, if you're paralleling two sets of 500 kcmil conductors per phase (common for large services), count each conductor separately. A three-phase installation with neutral and ground would have 10 total conductors (two per phase × three phases, plus two neutrals, plus two grounds).
Are these charts valid for both copper and aluminum conductors?
These specific charts show THHN/THWN copper conductors. Aluminum conductors of the same AWG size have identical insulation thickness and therefore identical cross-sectional area for fill calculations. However, aluminum requires larger conductors for equivalent ampacity, so you'll typically use larger wire sizes which have different fill values.
What if my calculation shows I can fit exactly X conductors - can I use that number?
Yes, if your calculation shows you can fit exactly a certain number of conductors without exceeding the fill percentage, that's the maximum allowed. However, many electricians prefer to leave margin when possible, as tightly-filled conduits are much more difficult to work with during installation and make future modifications challenging.
Do stranded and solid conductors have different fill values?
For sizes 8 AWG and smaller, NEC Table 5 provides values for solid conductors. For sizes 6 AWG and larger, values are for stranded conductors (as these are not commonly available in solid). The tables include the insulation thickness in all cases, so the overall diameter and cross-sectional area are what matter for fill calculations, regardless of conductor construction.
Keeping Current with Code Changes
The National Electrical Code updates on a three-year cycle. While conduit fill tables remain relatively stable between editions, changes do occur. The charts presented here reflect current NEC requirements as of 2024. Always verify you're using the code edition adopted by your local jurisdiction, which may lag behind the current national edition by one or more cycles.
Major changes to conduit fill requirements are rare, but when they occur, they typically involve:
- Addition of new conductor insulation types
- New conduit materials or specifications
- Clarifications on counting conductors for special applications
- Updates to compact conductor specifications
Conclusion
These comprehensive wire fill charts provide essential reference data for electrical professionals performing conduit installations. By understanding how to read and apply these tables correctly, you can quickly size conduit for any application while ensuring code compliance. Remember that these charts represent maximum permitted fills - leaving additional room often pays dividends in easier installation, better long-term performance, and flexibility for future modifications.
For installations involving mixed conductor sizes, unusual insulation types, or complex calculations, supplement these charts with our digital conduit fill calculators which handle any scenario while maintaining full NEC compliance. Whether using charts or calculators, proper conduit sizing protects your installations, satisfies inspectors, and demonstrates professional expertise.