Conduit Fill Calculator
Check conduit fill for EMT, IMC, rigid and PVC from ½ to 4 in under NEC Chapter 9, with the smallest size and the most wires that fit.
The National Electrical Code limits how much of a conduit's inside area the wires can take up: 53% for one wire, 31% for two and 40% for three or more (Chapter 9, Table 1). Four 12 AWG THHN wires take 0.0532 in², which is 17.5% of a ½ in EMT, so they fit. Three 3/0 and one 1/0 THHN take 0.989 in²: too much for 1½ in EMT, which allows 0.814 in², so they need 2 in. This calculator adds up the wires from Table 5 and checks them against EMT, IMC, rigid metal and PVC Schedule 40 and 80 conduit from Table 4, in every trade size from ½ to 4 in. It shows the smallest conduit that fits and, for wires all the same size, the most that fit in each size. A nipple of 24 in or less may be filled to 60%.
- Smallest conduit
- 1/2 in EMT
- 1/2 in EMT
- Fits
- Wire area
- 0.0532 in²
- Allowed area
- 0.1216 in²
17.5% full
17.5% full, 40% allowed
4 conductors
of 0.304 in² inside
| Trade size | Fill | Most of these wires | 40% allowed | Inside area |
|---|---|---|---|---|
| 1/2 in | 17.5% (fits) | 9 | 0.1216 in² | 0.304 in² |
| 3/4 in | 10% (fits) | 16 | 0.2132 in² | 0.533 in² |
| 1 in | 6.2% (fits) | 26 | 0.3456 in² | 0.864 in² |
| 1-1/4 in | 3.6% (fits) | 45 | 0.5984 in² | 1.496 in² |
| 1-1/2 in | 2.6% (fits) | 61 | 0.8144 in² | 2.036 in² |
| 2 in | 1.6% (fits) | 101 | 1.3424 in² | 3.356 in² |
| 2-1/2 in | 0.9% (fits) | 176 | 2.3432 in² | 5.858 in² |
| 3 in | 0.6% (fits) | 266 | 3.5384 in² | 8.846 in² |
| 3-1/2 in | 0.5% (fits) | 347 | 4.618 in² | 11.545 in² |
| 4 in | 0.4% (fits) | 443 | 5.9012 in² | 14.753 in² |
How it was worked out
- 4 × 12 AWG THHN / THWN-2 at 0.0133 in² = 0.0532 in²
- Total 4 conductors: 0.0532 in², so the limit is 40% (more than two)
- 1/2 in EMT: 0.304 in² × 40% = 0.1216 in² allowed; 0.0532 in² is 17.5% of the conduit
From NEC Chapter 9: Table 1 (fill limits), Table 4 (conduit areas) and Table 5 (wire areas). Count every wire, including an insulated equipment grounding conductor; bare wires and cables in conduit have their own areas and aren't covered here. "Most of these wires" applies Note 7, which rounds up when the answer's decimal is 0.8 or more. A full conduit is hard to pull through, especially with long runs and several bends. With more than three current-carrying wires together, their allowed current must be reduced (310.15(C)).
Common use cases
- Choose the conduit size for a new circuit or feeder
- Check whether another circuit will fit in an existing conduit
- Find the most THHN wires of one size a conduit can take
- Compare EMT, rigid and PVC for the same set of wires
How to use
- Choose the conduit type and the trade size to check.
- Enter each wire: insulation type, size and how many, including an insulated ground.
- Tick the nipple box for a run of 24 in or less.
- Read whether the conduit fits, how full it is and the smallest size that works.
- Use the table to compare every trade size.
FAQ
How many 12 AWG wires fit in ½ in EMT?
Nine 12 AWG THHN wires: 40% of ½ in EMT is 0.1216 in², and each wire is 0.0133 in². ¾ in EMT takes 16. In ½ in PVC Schedule 40, which is smaller inside, the answer is 8.
What are the conduit fill limits?
53% of the inside area for one wire, 31% for two and 40% for three or more, from NEC Chapter 9 Table 1. A nipple 24 in long or less may be filled to 60%.
Do ground wires count in conduit fill?
Yes. Equipment grounding and bonding conductors count toward fill. An insulated ground uses the same area as any other wire of its type and size; bare wires have smaller areas in Table 8.
What is the 0.8 rule?
Chapter 9 Note 7: when all the wires are the same size and the number that fits works out with a decimal of 0.8 or more, you may round up. 40% of ¾ in EMT divided by the area of a 14 AWG THHN wire is 21.98, so 22 fit.
Why does PVC hold fewer wires than EMT of the same trade size?
Trade size is a name, not a measurement. PVC has thicker walls, so its inside area is smaller: ½ in Schedule 40 PVC is 0.285 in² inside, against 0.304 in² for ½ in EMT.
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Results are estimates worked out from the figures you enter and published tables, for planning only. They are not electrical, engineering or professional advice. Mains electricity can kill and start fires. Check cable and circuit sizes against the wiring rules where you live (the NEC and local amendments in the US, BS 7671 in the UK, AS/NZS 3000 and 3008 in Australia and New Zealand), and use a licensed electrician where the law requires one.