TryBuildCalcConduit Fill Calculator (NEC Chapter 9 Tables 1, 4 & 5)
Calculate conduit fill instantly.
🕒 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
ℹ️EMT, PVC Schedule 40, and RMC have slightly different internal areas at the same trade size — the result compares all three.
Recommended Conduit Size: 1/2" EMT (Electrical Metallic Tubing)
4 conductors, 17.5% fill (max allowed 40%)
Conductor Breakdown
| Conductor | AWG | Qty | Area |
|---|---|---|---|
| Hot | 12 AWG | × 2 | 0.0266 in² |
| Neutral | 12 AWG | × 1 | 0.0133 in² |
| Ground | 12 AWG | × 1 | 0.0133 in² |
| Total | 4 conductors | 0.0532 in² |
Fill Calculation
Total conductor area: 0.0532 in²
Allowed fill (NEC Table 1, 4 conductors): 40%
1/2" EMT (Electrical Metallic Tubing) internal area: 0.304 in² (0.1216 in² allowed at 40%)
Actual fill achieved: 17.5%
Trade Size by Conduit Type
| Conduit Type | Required Trade Size |
|---|---|
| EMT (Electrical Metallic Tubing) | 1/2" |
| PVC Schedule 40 | 1/2" |
| RMC (Rigid Metal Conduit) | 1/2" |
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.
General conduit fill estimate
This page gives the full combined result — total conductor area, allowed fill, and required trade size across all three supported conduit types — from one conductor list.
It's the same calculator behind every other conduit-sizing variant on this site, just without a specific scenario pre-selected — useful for a general check before finalizing your actual conductor list.
- Supports a genuinely mixed conductor list — different AWG sizes together in one conduit.
- Applies the correct NEC Table 1 fill percentage automatically based on your conductor count.
- Compares required trade size across EMT, PVC Schedule 40, and RMC simultaneously.
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 | 3 distinct sizes, 4 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 |
|---|---|---|
| Hot | 12 AWG area × 2 | 0.0266 in² |
| Neutral | 12 AWG area × 1 | 0.0133 in² |
| Ground | 12 AWG area × 1 | 0.0133 in² |
| Total | 0.0532 in² |
Step 2 — Allowed Fill Percentage
Set once by your total conductor count, per NEC Chapter 9 Table 1.
| Allowed fill (4 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 0.0532 in²? |
|---|---|---|---|
| 1/2" | 0.304 × 40% | 0.1216 in² | Yes — this is the answer |
Therefore, for 4 conductors (0.0532 in² total) in EMT (Electrical Metallic Tubing), you need 1/2" (0.304 in² total, 0.1216 in² allowed at 40%), running at 17.5% 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.