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Conduit Fill Calculator

Pick EMT or Schedule 40 PVC, a trade size, and how many THHN or THWN-2 conductors of each gauge you plan to pull. The calculator compares the wires’ combined cross-section to the conduit’s internal area and to the Code’s 53, 31 and 40 percent fill limits.

THHN / THWN-2 copper — enter a count for each size you are pulling. Leave unused sizes at 0.

Your estimate

Fill

14.9%

Under the 40% limit for 6 conductors.

Wire area

0.08 in²

6 conductors

Conduit area

0.533 in²

EMT 3/4 in

Allowed fill

0.213 in²

40% of the internal area

Remaining

0.134 in²

Headroom under the limit

The 53 / 31 / 40 percent limits are the National Electrical Code Chapter 9, Table 1 rules for 1, 2, and 3 or more conductors. Outside diameters are manufacturer THHN/THWN-2 figures; internal diameters are manufacturer EMT and Schedule 40 PVC figures. This is a planning check, not a substitute for the Code, an electrician, or the inspector. It does not size the conductors or check voltage drop.

Estimates only — confirm with your supplier and local code. First published · Last reviewed by CalcTheJob.

How to use the conduit fill calculator

  1. Choose the raceway — EMT or Schedule 40 PVC — and the trade size.
  2. Enter a count for each conductor size you will pull (THHN / THWN-2 copper). Leave unused sizes at zero. A ground counts as a conductor for fill.
  3. Read the fill percentage, the allowed percentage, and whether the pull is under the limit. Remaining area is the headroom under that limit.

This is a planning check. It does not select the wire size or test voltage drop — use the voltage drop calculator for run length and gauge.

How fill is computed, without copying Code tables

Each conductor’s area is π × (outside diameter ÷ 2)². Diameters are manufacturer figures for copper THHN/THWN-2 (for example 12 AWG is 0.130 in, 10 AWG is 0.164 in). The conduit area uses the manufacturer internal diameter (¾ in EMT is 0.824 in; ¾ in Schedule 40 PVC is 0.804 in).

The National Electrical Code, Chapter 9, Table 1, sets the maximum fill at 53% for one conductor, 31% for two, and 40% for three or more. Those three percentages are the rule this page applies. It does not reproduce the Code’s conductor-count tables; it computes fill from the dimensions instead, so a mixed pull of several sizes is handled the same way as a pull of one size.

A worked example: six 12 AWG THHN in ¾ in EMT

One 12 AWG THHN has an area of π × (0.130 ÷ 2)² = 0.01327 in². Six of them are 0.07964 in². A ¾ in EMT has an internal area of π × (0.824 ÷ 2)² = 0.5333 in². Fill = 0.07964 ÷ 0.5333 = 14.9%. With six conductors the limit is 40%, or 0.213 in², so the pull is well under the limit and about 0.134 in² of area remains.

Sources & assumptions

How this calculator gets its numbers. Full method: our methodology.

  • Wire area is computed from manufacturer THHN/THWN-2 outside diameters; conduit area from manufacturer EMT or Schedule 40 PVC internal diameters.
  • Maximum fill is 53% (1 conductor), 31% (2) or 40% (3 or more), from NEC Chapter 9, Table 1.
  • The page does not reproduce copyrighted NEC conductor-count tables.
  • A passing fill result does not size the conductors or check voltage drop.

Sources

  1. NFPA, National Electrical Code (2023), Chapter 9, Table 1. Maximum percent fill: 53% (1 conductor), 31% (2), 40% (3 or more). The table itself is not reproduced here.
  2. Southwire, Building Wire — THHN/THWN-2 copper specifications. Manufacturer outside diameters used for copper THHN/THWN-2 (for example 12 AWG 0.130 in, 10 AWG 0.164 in).
  3. Allied Tube & Conduit, EMT electrical metallic tubing data. Manufacturer internal diameters for EMT trade sizes (¾ in EMT ID 0.824 in).
  4. Carlon / Atkore, Schedule 40 PVC conduit specifications. Manufacturer internal diameters for Schedule 40 PVC conduit (¾ in ID 0.804 in).

Last reviewed . Product figures vary by brand; the label on what you buy wins.

Frequently asked questions

What is the NEC fill limit for three or more conductors?

40% of the conduit’s internal cross-section, from NEC Chapter 9, Table 1. One conductor is allowed 53%, and two conductors 31%.

Can I pull six 12 AWG THHN wires in ¾ inch EMT?

Yes, as a fill check: six 12 AWG THHN occupy about 14.9% of ¾ in EMT, under the 40% limit. Always confirm the pull with your electrician and the inspector, and check voltage drop separately.

Why doesn’t this page show a table of maximum wires per pipe?

Those count tables are copyrighted Code material. Computing fill from manufacturer diameters and the 53/31/40 percent rule gives the same check for mixed sizes without reproducing the tables.

Does a passing fill result mean the wire size is correct?

No. Fill only asks whether the conductors fit. Ampacity, voltage drop, derating and the equipment grounding conductor are separate checks.

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