Conduit Fill Calculator
10 × 12 AWG in 3/4" EMT: 25.0% fill. Within the 40% limit.
- Fill
- 25.0%
- Allowed (Ch. 9 Table 1)
- 40%
- Maximum conductors of this size
- 16
- Conduit area (Table 4)
- 0.533 in²
- Conductor area (Table 5)
- 0.0133 in² each
Add each group of conductors (quantity, size and insulation type), choose the raceway type, and the calculator returns the total conductor area, the percent fill for each trade size, and the smallest raceway that stays within NEC limits.
How conduit fill is calculated
The NEC sets conduit fill limits in Chapter 9. Three tables do the work:
- Table 1 sets the maximum percent of the raceway's internal area that conductors may occupy.
- Table 4 gives the internal area of each raceway type and trade size (EMT, IMC, RMC, PVC Schedule 40 and 80, ENT, flexible conduits).
- Table 5 gives the approximate area of each insulated conductor, by insulation type and size. Compact conductors use Table 5A.
The maximum fill depends on how many conductors are in the raceway:
| Number of conductors | Maximum fill |
|---|---|
| 1 | 53% |
| 2 | 31% |
| Over 2 | 40% |
Two conductors get the lowest percentage because two round cables can jam against each other during a pull. Short nipples up to 24 inches long may be filled to 60% (Chapter 9, Note 4). Equipment grounding and bonding conductors count toward the fill.
Worked example: a mixed set in EMT
You need to pull three 6 AWG THHN, one 8 AWG THHN and one 10 AWG THHN ground in EMT.
- Conductor areas (Table 5): 6 AWG THHN = 0.0507 in²; 8 AWG = 0.0366 in²; 10 AWG = 0.0211 in².
- Total area: (3 × 0.0507) + 0.0366 + 0.0211 = 0.2098 in².
- Allowed fill: five conductors, so 40%.
- Pick the raceway (Table 4, 40% column for EMT): ½" = 0.122 in² (too small); ¾" = 0.213 in² (0.2098 fits, at 39.4% fill). ¾" EMT passes.
The same set does not fit ¾" PVC Schedule 40, whose 40% area is only 0.203 in²; it needs 1" PVC (0.333 in² allowed, 25.2% fill). Check the raceway type before you copy a size from an EMT run.
The ¾" EMT is close to its limit. It is legal, but the pull will be tight. Many electricians go up a size when fill is above about 35%, especially with bends.
How many wires fit in a conduit? (quick charts)
When all conductors are the same size and type, NEC Annex C lists the maximum number directly. These counts are computed from Chapter 9 Tables 1, 4 and 5 for THHN/THWN-2, including Note 7 (when the calculation ends in a decimal of 0.8 or more, you may round up one conductor).
EMT (electrical metallic tubing):
| THHN/THWN-2 | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" |
|---|---|---|---|---|---|---|
| 14 AWG | 12 | 22 | 35 | 61 | 84 | 138 |
| 12 AWG | 9 | 16 | 26 | 45 | 61 | 101 |
| 10 AWG | 5 | 10 | 16 | 28 | 38 | 63 |
| 8 AWG | 3 | 6 | 9 | 16 | 22 | 36 |
| 6 AWG | 1 | 4 | 7 | 12 | 16 | 26 |
| 4 AWG | 1 | 2 | 4 | 7 | 10 | 16 |
| 3 AWG | 1 | 1 | 3 | 6 | 8 | 13 |
| 2 AWG | 1 | 1 | 3 | 5 | 7 | 11 |
| 1 AWG | 1 | 1 | 1 | 4 | 5 | 8 |
| 1/0 AWG | 0 | 1 | 1 | 3 | 4 | 7 |
| 2/0 AWG | 0 | 1 | 1 | 2 | 3 | 6 |
| 3/0 AWG | 0 | 1 | 1 | 1 | 3 | 5 |
| 4/0 AWG | 0 | 0 | 1 | 1 | 1 | 4 |
PVC Schedule 40:
| THHN/THWN-2 | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" |
|---|---|---|---|---|---|---|
| 14 AWG | 11 | 21 | 34 | 60 | 82 | 135 |
| 12 AWG | 8 | 15 | 25 | 43 | 59 | 99 |
| 10 AWG | 5 | 9 | 15 | 27 | 37 | 62 |
| 8 AWG | 3 | 5 | 9 | 16 | 21 | 36 |
| 6 AWG | 1 | 4 | 6 | 11 | 15 | 26 |
| 4 AWG | 1 | 1 | 4 | 7 | 9 | 16 |
| 3 AWG | 1 | 1 | 3 | 6 | 8 | 13 |
| 2 AWG | 1 | 1 | 3 | 5 | 7 | 11 |
| 1 AWG | 0 | 1 | 1 | 3 | 5 | 8 |
| 1/0 AWG | 0 | 1 | 1 | 3 | 4 | 7 |
| 2/0 AWG | 0 | 1 | 1 | 2 | 3 | 6 |
| 3/0 AWG | 0 | 1 | 1 | 1 | 3 | 5 |
| 4/0 AWG | 0 | 0 | 1 | 1 | 1 | 4 |
For the same charts with common feeder and circuit combinations worked out, see the conduit fill chart. For PVC Schedule 80 and other insulation types, use the calculator above.
Conduit fill is not the only limit
Passing the fill check does not mean the installation is complete:
- Ampacity adjustment. More than three current-carrying conductors in one raceway require ampacity adjustment under 310.15(C)(1): 80% for 4–6 conductors, 70% for 7–9, 50% for 10–20. A raceway that passes fill can still force you to upsize the wire.
- Bends. No more than 360° of bends between pull points.
- Pulling tension. Long pulls with several bends may need a larger conduit than fill alone suggests, to keep tension and sidewall pressure within the cable manufacturer's limits.
- Future capacity. Spare room in a raceway is cheap during rough-in and expensive later.
Frequently asked questions
How many 12 gauge wires can go in a 1/2 inch conduit?
In ½" EMT, up to 9 conductors of 12 AWG THHN. In ½" PVC Schedule 40, up to 8. Remember to derate ampacity when more than three are current-carrying.
How many 12 gauge wires can go in 3/4 conduit?
Up to 16 conductors of 12 AWG THHN in ¾" EMT and 15 in ¾" PVC Schedule 40.
Does the ground wire count toward conduit fill?
Yes. Every conductor in the raceway, including equipment grounding and bonding conductors, counts toward fill. Grounding conductors do not count as current-carrying conductors for ampacity adjustment.
What is the 40% rule for conduit?
When a raceway contains more than two conductors, their total cross-sectional area may not exceed 40% of the raceway's internal area (NEC Chapter 9, Table 1).
Can I use the same chart for Romex (NM cable) in conduit?
No. Cables are treated differently: a multiconductor cable is counted as one conductor using its overall area, and an oval cable is treated as a round cable with a diameter equal to its major dimension (Chapter 9, Note 9).
Related
Counting runs and raceways on a whole set of plans? SparkQuote measures conduit runs and counts devices on PDF drawings, then turns them into a priced material list. See electrical takeoff in SparkQuote.
Last updated: October 6, 2026. Based on NEC 2023 Chapter 9; values unchanged in Table 4 since the 2020 edition. Check results against the code edition and local amendments your jurisdiction enforces and with the AHJ; electrical work should be done by qualified people.