Conduit Fill Calculator

Add the THHN/THWN conductors you're pulling (including the equipment grounding conductor), pick a conduit type and size, and check the total conductor area against the governing NEC fill limit. If you're over, the tool recommends the smallest conduit that fits.

Conduit

Conduit Type

Conduit Size

Nipple (≤24" between boxes) — 60% fill, Table 1 Note 4

Conductors

Equipment Ground (EGC)

Non-THHN insulations (XHHW, RHW, …) and PVC Sch 80 show as “pending” until their NEC Table 5 / Table 4 areas are verified.

Results

Total Wire Area0.0399 in²

Conductors (incl. EGC)3

Fill Used4.6%

NEC limit (40%)0.3456 in²

Per-conductor area

3× 12 AWG THHN0.0399 in²

✓ EMT 1" meets the NEC 40% fill

NEC Ch. 9 — Table 1 (max fill: 53% one / 31% two / 40% over two / 60% nipple), Table 4 (raceway area), Table 5 (conductor area).

Method: conductor areas from NEC Chapter 9, Table 5 (THHN/THWN) are summed and compared to the maximum fill from NEC Chapter 9, Table 1 — 53% for one conductor, 31% for two, 40% for three or more (60% for a nipple ≤24"; Note 4) — of the raceway area from Table 4. The equipment grounding conductor counts toward fill. Verify against the governing edition of the NEC for your jurisdiction.

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