TryBuildCalcMixed Wire Size Conduit Fill Calculator (Multiple Different Conductor Sizes, One Conduit)
Calculate fill for mixed wire sizes.
🕒 Last updated: August 29, 2026
Inputs
Conductors
Add every conductor being pulled through this conduit — mix as many different wire sizes as needed.
Conductor 1
Conductor 2
Conductor 3
Conductor 4
ℹ️EMT, PVC Schedule 40, and RMC have slightly different internal areas at the same trade size — the result compares all three.
Recommended Conduit Size: 3/4" EMT (Electrical Metallic Tubing)
9 conductors, 36.6% fill (max allowed 40%)
Conductor Breakdown
| Conductor | AWG | Qty | Area |
|---|---|---|---|
| Large Hot | 6 AWG | × 2 | 0.1014 in² |
| Branch Circuit Hot | 12 AWG | × 4 | 0.0532 in² |
| Control Wire | 14 AWG | × 2 | 0.0194 in² |
| Ground | 10 AWG | × 1 | 0.0211 in² |
| Total | 9 conductors | 0.1951 in² |
Fill Calculation
Total conductor area: 0.1951 in²
Allowed fill (NEC Table 1, 9 conductors): 40%
3/4" EMT (Electrical Metallic Tubing) internal area: 0.533 in² (0.2132 in² allowed at 40%)
Actual fill achieved: 36.6%
Trade Size by Conduit Type
| Conduit Type | Required Trade Size |
|---|---|
| EMT (Electrical Metallic Tubing) | 3/4" |
| PVC Schedule 40 | 3/4" |
| RMC (Rigid Metal Conduit) | 3/4" |
Assumptions Used
Conductor areas per NEC Chapter 9 Table 5 (THHN/THWN-2 insulation). Fill limits per NEC Chapter 9 Table 1 (53% for 1 conductor, 31% for 2, 40% for 3 or more). This is a reference estimate — confirm with a licensed electrician before installation.
Need to check whether each conductor is correctly sized for its load first? Wire Size Calculator →
Sizing the breaker for this circuit next? Circuit Breaker Size Calculator →
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Conduit Fill Calculator.
Mixed wire size conduit fill
This page is pre-set to a genuinely mixed scenario — larger feeder conductors, smaller branch circuit wires, control wiring, and a ground, all sharing one conduit run.
This is the exact use case this calculator was built for — the Wire Size Calculator's own built-in conduit fill toggle can't model a mix like this.
- Add one row per distinct conductor size — no limit to how many different sizes you can mix.
- The total fill percentage is based on the sum of every conductor's individual area, not an average.
- Confirm all the different circuits/voltage classes you're combining are actually permitted to share one conduit before finalizing.
Conduit Fill Formula: How Is It Calculated?
Three NEC Chapter 9 tables work together: conductor areas, allowable fill percentage, and conduit internal areas.
Step 1 — Total Conductor Area
Total Area (in²) = Sum of every conductor's (AWG area × quantity)
Each conductor's cross-sectional area comes from NEC Chapter 9 Table 5 (THHN/THWN-2 insulation).
Step 2 — Allowable Fill Percentage
1 conductor: 53% max fill
2 conductors: 31% max fill
3+ conductors: 40% max fill
Per NEC Chapter 9 Table 1 — based purely on total conductor count, regardless of size.
Step 3 — Required Trade Size
Find smallest trade size where: Conduit Area × Fill % ≥ Total Conductor Area
Checked against NEC Chapter 9 Table 4's internal area for your chosen conduit type (EMT, PVC Schedule 40, or RMC).
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Conductors | 4 distinct sizes, 9 total | Sets total area and fill percentage tier |
| Conduit Type | EMT (Electrical Metallic Tubing) | Sets internal area per trade size |
Step 1 — Conductor Area per Row
| Conductor | Calculation | Area |
|---|---|---|
| Large Hot | 6 AWG area × 2 | 0.1014 in² |
| Branch Circuit Hot | 12 AWG area × 4 | 0.0532 in² |
| Control Wire | 14 AWG area × 2 | 0.0194 in² |
| Ground | 10 AWG area × 1 | 0.0211 in² |
| Total | 0.1951 in² |
Step 2 — Allowed Fill Percentage
Set once by your total conductor count, per NEC Chapter 9 Table 1.
| Allowed fill (9 conductors, 3+ tier) | 40% |
Step 3 — Checking Each Trade Size in Order
Starting from the smallest EMT (Electrical Metallic Tubing) size, each one is checked until the first that has enough allowed area is found.
| Trade Size | Calculation | Allowed Area | Fits 0.1951 in²? |
|---|---|---|---|
| 1/2" | 0.304 × 40% | 0.1216 in² | No — too small |
| 3/4" | 0.533 × 40% | 0.2132 in² | Yes — this is the answer |
Therefore, for 9 conductors (0.1951 in² total) in EMT (Electrical Metallic Tubing), you need 3/4" (0.533 in² total, 0.2132 in² allowed at 40%), running at 36.6% actual fill.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.