Conduit fill calculator
A 3/4 inch EMT conduit holds up to 16 THHN wires of 12 AWG. Wires may fill at most 40% of a conduit's inside area when there are three or more, 31% for two and 53% for one. Pick the conduit, add the wires and see how full it is.
Fits within the 40% limit for three or more wires.
- Wires
- 5
- Wire area
- 0.0665 in²
- Inside 3/4 in. EMT
- 0.533 in²
- Smallest that fits
- 1/2 in. EMT
How it is calculated
- 4 × 12 AWG THHN
- 1 × 12 AWG THHN
- Fill = 0.0665 ÷ 0.533 = 12.5%
How to calculate conduit fill
Conduit fill compares the cross-section of the insulated wires with the inside area of the conduit. The worked numbers use the calculator's default: 5 THHN wires of 12 AWG in 3/4 inch EMT.
Step 1: total area of the wires
Wire area = sum of (number of wires × area of one insulated wire), ground included
Example 5 × 0.0133 in² (12 AWG THHN) = 0.0665 in²
Step 2: percent of the conduit filled
Fill % = wire area ÷ inside area of the conduit × 100
Example 0.0665 in² ÷ 0.533 in² (3/4 in EMT) × 100 = 12.5%
Inside areas differ by conduit type: PVC has a thicker wall than EMT, so the same trade size holds less.
Step 3: compare with the fill limit
Limit = 53% for one wire, 31% for two, 40% for three or more
Example 5 wires: limit 40%. 12.5% is within it, so the conduit holds them.
Example The smallest EMT that holds them is 1/2 in, at 21.9%.
Step 4: most wires of one size
Wires = inside area × 40% ÷ area of one wire
When every wire is the same size, a decimal of 0.8 or more rounds up to the next whole wire
Example 0.533 in² × 40% ÷ 0.0133 in² = 16.03 → 16 wires of 12 AWG in 3/4 in EMT
Wire area allowed in a conduit by trade size
At the 40% limit for three or more wires, 3/4 inch EMT allows 0.213 in² of wire, and 3/4 inch PVC Sch 80 allows 0.164 in². Add up the areas of your wires (step 1 above) and pick the first size whose allowed area is larger. Wire counts by size for every conduit: Conduit fill chart.
| Trade size | EMT, in² | PVC Sch 40, in² | PVC Sch 80, in² | RMC, in² |
|---|---|---|---|---|
| 1/2 in | 0.122 | 0.114 | 0.087 | 0.126 |
| 3/4 in | 0.213 | 0.203 | 0.164 | 0.22 |
| 1 in | 0.346 | 0.333 | 0.275 | 0.355 |
| 1-1/4 in | 0.598 | 0.581 | 0.495 | 0.61 |
| 1-1/2 in | 0.814 | 0.794 | 0.684 | 0.828 |
| 2 in | 1.342 | 1.316 | 1.15 | 1.363 |
- EMT
- PVC Sch 40
- PVC Sch 80
- RMC
What conduit fill does not cover
Fill is about pulling wire without damaging it. With more than three current-carrying wires in one conduit, each one must also be derated, which can force a larger wire size. Long pulls and many bends need more room than the limit allows.