Preliminary numbers for estimating and for checking a quote or a plan. The NEC edition your local authority having jurisdiction adopted comes first. A licensed electrician sizes and installs the raceway.

Maintained by BuildSolver · Updated October 20, 2026

Calculator · Electrical

Conduit fill calculator

Three 500 kcmil XHHW wires and a 1/0 AWG XHHW ground wire add up to 2.2777 sq in. In PVC Schedule 80 they need a 3 in. conduit, which allows 2.5768 sq in at 40 %. This page adds up the wire areas of Table 5, takes the limit that Table 1 sets for that many wires, and finds the smallest trade size of the conduit type that passes. It also gives the most wires of one size that fit, with the Note 7 rounding. Two wires get only 31 %, less than the 40 % for three, so check a pair first. It checks fill, not ampacity. For the wire use the AC wire size calculator.

Choose the conduit or tubing type, a trade size or the smallest that passes, and say whether it is a nipple of 24 in. or less between boxes.
Pick the insulation, size and number of wires for each group, up to three groups, and add the ground wire as its own group. Every wire counts, the ground wire too.
The result shows the total wire area, the area the conduit allows at the Table 1 percent, how full the conduit is, and the smallest trade size of that type that passes.

Fill for single building wires, 14 AWG to 1000 kcmil, in EMT, IMC, RMC, PVC Schedule 40 or 80, ENT or FMC. Not ampacity, cable or bare wire. A licensed electrician installs the raceway.

Conduit or tubing type

Table 4 gives a different inside area to each type. PVC Schedule 80 has a thicker wall than Schedule 40 and holds less. ENT is made to 2 in., EMT, IMC and FMC to 4 in., RMC and PVC to 6 in.

Trade size

Pick a size to test it, or let the page find the smallest size of this type that passes. The page also shows the smallest size when you pick one.

Nipple of 24 in. or less between boxes

Note 4 lets a short nipple between boxes, cabinets or similar enclosures be filled to 60 %. A longer conduit takes the Table 1 limits.

Group 1 insulation

Insulation type of the first group of wires. Table 5 gives each type its own area.

Group 1 wire size

Group 1 number of wires

A whole number. Count every wire of this size and type that runs through the conduit.

Group 2 insulation

A second size or type in the same conduit. Leave as none if there is no second group.

Group 3 insulation

A third size or type. Leave as none if there is no third group.

Ground wire insulation

Note 3 counts the equipment grounding and bonding wires in the fill. Pick the insulation of an insulated ground wire, and set the number to 0 if there is no ground wire. A bare ground wire is smaller than the insulated size shown here, so the page overstates it slightly.

Ground wire size

Number of ground wires

A whole number, 0 when the conduit carries no ground wire (a metal raceway used as the ground, for example).

Example result for the default inputs

PVC Schedule 80, trade size 3 (smallest that passes), 4 conductors. NEC Chapter 9.

Conductor area

2.2777 in²

Allowed at 40 %

2.5768 in²

Conduit fill

35.4 %

Smallest PVC Schedule 80

3 in.

Calculation details
3 x 500 kcmil XHHW	3 x 0.6984 = 2.0952 sq in (Table 5).
1 x 1/0 AWG XHHW ground	1 x 0.1825 = 0.1825 sq in (Table 5).
Total conductor area	2.2777 sq in for 4 conductors, the ground wire included (Note 3).
Fill limit	40 % for 4 conductors, more than two (Table 1).
PVC Schedule 80, trade size 3, smallest that passes	6.442 sq in inside (Table 4, Article 352). 40 % of that is 2.5768 sq in.
Result	2.2777 sq in is within the 2.5768 sq in allowed. The conduit is 35.4 % full.
Smallest PVC Schedule 80 that passes	Trade size 3.

The conductors are not all one size, so Note 7 does not apply and the plain area is used.

For estimation purposes only. Consult a licensed engineer for final designs.

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How conduit fill is worked

Conduit fill is a limit on how much of the inside of a conduit the wires may take up. NEC Chapter 9 sets it as a percent of the inside cross-section: 53 % for one wire, 31 % for two, 40 % for more than two. You add up the area of every wire, ground wires included, and compare the sum with that percent of the conduit area. When every wire is the same size, Note 7 lets the count round up. This is a fit rule. It does not tell you how many wires the circuit may carry.

Conductor area: sum of (number of wires x area of one wire from Table 5)Insulation counts, so the area depends on the type. A 12 AWG THHN is 0.0133 sq in, a 12 AWG XHHW is 0.0181 sq in. On the default, 3 x 500 kcmil XHHW and a 1/0 AWG XHHW ground give 2.2777 sq in.
Fill limit: 53 % for 1 wire, 31 % for 2, 40 % for more than 2, 60 % for a nipple of 24 in. or lessTable 1 and Note 4. Count every wire, the ground wire too (Note 3). In 1/2 in. EMT, with 0.3040 sq in inside, that is 0.1611 sq in for one wire, 0.0942 for two, 0.1216 for three or more and 0.1824 for a nipple.
Allowed area: limit percent x total inside area of the conduit, Table 4The default conduit, PVC Schedule 80 in trade size 3, has 6.4420 sq in inside. At 40 % it allows 2.5768 sq in. Table 4 prints its percent columns to three decimals and the copies differ by a thousandth, so this page takes the percent of the total itself.
Same-size rounding, Note 7: allowed area / area of one wire, rounded up when the decimal is 0.8 or moreOnly when every wire has the same area. 1.3164 sq in / 0.2642 sq in = 4.98, so 5 wires of 3/0 AWG XHHW fit in 2 in. PVC Schedule 40 although their area, 1.3210 sq in, is a little over the limit. Annex C lists this count.
Smallest trade size: first size of the chosen type, smallest up, where the wires fitThe page tries each size of the type in turn. The same five 3/0 AWG wires need 2 in. in Schedule 40 and 2-1/2 in. in Schedule 80, because Schedule 80 has the thicker wall.

Eight sets of wires through the same formula

The first seven rows are worked examples from David Snyder's PDHonline course and Mike Holt in EC&M, and the page gives the same trade sizes. The last row shows the two-wire limit: a 1/0 AWG and a 2 AWG THHN pair needs 1-1/4 in. EMT, and with an 8 AWG ground wire in the conduit it fits 1 in.

Wires, conduit, wire area, fill limit and smallest trade size for eight sets of wires
Circuit	Conduit	Wires	Area, sq in	Limit, %	Smallest trade size, in.
3 x 500 kcmil and a 1/0 ground, XHHW, PVC 80 (Snyder)	PVC Schedule 80	4	2.2777	40	3
3 x 500, 1 x 250 and 1 x 3 AWG THHN, PVC 40 (Mike Holt)	PVC Schedule 40	5	2.6162	40	3
5 x 3/0 XHHW, PVC 40, Note 7 (Snyder)	PVC Schedule 40	5	1.3210	40	2
5 x 3/0 XHHW, PVC 80 (Snyder)	PVC Schedule 80	5	1.3210	40	2-1/2
3 x 8 AWG and 2 x 10 AWG THWN, PVC 80 (Snyder)	PVC Schedule 80	5	0.1520	40	3/4
6 x 4/0 XHHW and 2 x 6 AWG ground, RMC nipple (Snyder)	RMC	8	2.0196	60	2
2 x 8 AWG THWN, EMT (Snyder)	EMT	2	0.0732	31	1/2
1/0 and 2 AWG THHN with an 8 AWG ground, EMT	EMT	3	0.3379	40	1

Five 3/0 AWG XHHW wires add up to 1.3210 sq in, a little over the 1.3164 sq in of 2 in. Schedule 40 PVC, and they still fit because the wires are all one size and the quotient, 4.98, rounds up under Note 7. In Schedule 80 the same wires need 2-1/2 in. The RMC nipple passes in 2 in. at 60 % and needs 3 in. as a longer run. In 1 in. EMT the pair is 34.9 % full, over its 31 % limit.

Standards and data sources

NEC 2023, Chapter 9 Tables 1, 4, 5 and the Notes to Tables, and Annex C - the fill percentages, the conduit areas, the wire areas, the notes on ground wires, nipples and same-size wires, and the Annex C counts. The NEC text was read as others print it, not in NFPA's viewer.
David A. Snyder, PE, PDHonline course E276, Conduit Fill Calculations - Table 1 and Notes 3, 4, 5, 7 and 9 as he restates them, conduit tables for EMT, IMC, RMC and both PVC schedules, a Table 5 extract up to 500 kcmil, and the worked examples that this page opens on.
Mike Holt Enterprises, Electrical Exam Preparation unit 5.7 (2020 NEC), and EC&M Code Q&A, Sizing a Raceway - answers printed from Annex C (8 THHN in 3/4 in. EMT is 6, 12 THHN in 1 in. EMT is 26, 6 XHHW in 1 in. ENT is 5) and the 3 x 500 kcmil, 250 kcmil and 3 AWG THHN example in Schedule 40 PVC.
Elliott Electric Supply conduit fill charts and Texas Residential Code 2024 Tables E3904.6 - 2,812 published Annex C counts that the page is tested against: THHN for six conduit types, and THHN, XHHW and THW for six types in sizes 1/2 to 2 in. The two sources agree except where a count sits on the 0.8 rounding line.
NECA Table 4 copy, conduit.site and the ICC study sample of Table 5 - the total inside area and inside diameter of each conduit size, and the wire areas for THHN, XHHW and THW from 14 AWG to 1000 kcmil. Two copies agree on every value used.

Limitations of this calculator

This page gives preliminary numbers for estimating and for checking a quote or a plan. A licensed electrician sizes and installs the raceway under the permit and the inspection of the local authority having jurisdiction (AHJ). Nothing here is an approval of an installation.
Fill is not ampacity. With more than three current-carrying wires in a conduit, 310.15(C)(1) lowers the allowed current, and that often calls for larger wire. Use the AC wire size calculator for the wire and the voltage drop calculator for the run. A nipple of 24 in. or less is exempt from that adjustment under Note 4.
The NEC text was read as Snyder, Mike Holt, EC&M and the published tables print it, not in NFPA's own viewer, and the tables are those of the 2020 NEC or an older edition. The 2023 pages of Tables 4 and 5 were not read, so the values here are those of the 2020-era copies. Check the edition your AHJ adopted.
Wire areas are for round, concentric-lay-stranded wire with the insulation types listed: THHN, THWN, THWN-2, XHHW, XHHW-2, XHH, TW, THW, THW-2 and THHW, 14 AWG to 1000 kcmil. Compact-stranded wire (Table 5A), RHH and RHW, fixture wire, bare wire (Table 8) and sizes above 1000 kcmil are not included. A bare ground wire is smaller than the insulated size shown, so the page overstates it.
Multiconductor cable, flexible cord and fiber cable count as one conductor with their actual dimensions (Notes 5 and 9). The page does not take cable. Armored cable, NM cable and conduit bodies are outside it.
Conduit types are EMT, IMC, RMC, PVC Schedule 40 and 80, ENT and FMC. LFMC and LFNC are left out because the copies of Table 4 and the published counts did not agree on their areas. ENT is made to 2 in., EMT, IMC and FMC to 4 in., RMC and PVC to 6 in. HDPE, PVC Type A and Type EB are not included.
Table 1 applies to a complete conduit system. Note 2 says it does not apply to a short sleeve that only protects exposed wiring from physical damage. The page does not tell the two apart.
The page does not check the jam ratio, the length of the pull, the bends, the pulling tension or the minimum size a specification requires, and it picks sizes as small as 1/2 in. when they pass. Where a published count sits within 0.003 of the 0.8 rounding line, the two readings of Table 4 give different counts, and the page reports the lower one.

Common mistakes with conduit fill

Leaving the ground wire out. Note 3 counts equipment grounding and bonding wires in the fill. Three 2 AWG THHN wires are 0.3474 sq in and fit 1 in. EMT, a count Annex C prints. Add the 8 AWG ground wire that goes with them and the conductors are no longer one size: 0.3840 sq in, over the 0.3456 sq in that 1 in. EMT allows, and the smallest EMT is 1-1/4 in.
Using 40 % for two wires. Two wires are held to 31 %, less than the 40 % for three. A 1/0 AWG and a 2 AWG THHN are 0.3013 sq in, over the 31 % of 1 in. EMT, so the pair needs 1-1/4 in. With an 8 AWG ground wire in the same conduit there are three conductors at 40 %, the total is 0.3379 sq in, and 1 in. passes. The extra wire made a smaller conduit legal.
Rounding up when the wires are different sizes. Note 7 applies only when every wire has the same area. Five 3/0 AWG XHHW wires fit 2 in. PVC Schedule 40 by Note 7 although the sum is 1.3210 sq in against 1.3164 sq in allowed. Add one more wire of another size and the plain sum is the test, and the answer changes.
Using an Annex C count for mixed sizes. Annex C tables are for wires that are all the same size. For a mix, Chapter 9 sends you to Table 5 for the wire areas and Table 4 for the conduit, which is what this page does. A count read off an Annex C table for one of the sizes in a mix says nothing about the others.
Taking THHN areas for XHHW wire. Insulation thickness changes the area. In 1 in. EMT 26 wires of 12 AWG THHN fit but only 19 of 12 AWG XHHW, because XHHW is 0.0181 sq in against 0.0133 sq in. In Table 5, XHHW is the thicker wire from 14 to 6 AWG and from 600 kcmil up, and slightly thinner from 4 AWG to 500 kcmil. Pick the type printed on the wire.
Giving a long run the nipple limit. The 60 % limit is for a nipple of 24 in. or less between boxes or enclosures. The RMC nipple on this page, 6 x 4/0 AWG XHHW and two 6 AWG ground wires, passes in 2 in. at 60 %. The same wires in a longer conduit take 40 % and need 3 in.

Common questions about conduit fill

How many 12 gauge wires fit in 1/2 inch conduit?

9 wires of 12 AWG THHN fit 1/2 in. EMT, 16 fit 3/4 in. and 26 fit 1 in. (Annex C, Table C.1). For 14 AWG THHN the counts are 12 and 22, and for 10 AWG THHN 5 and 10. These are fill counts at 40 %. They do not mean the circuit may carry that many current-carrying wires; ampacity drops once there are more than three. In 1/2 in. PVC Schedule 40 the 12 AWG THHN count is 8, and in Schedule 80 it is 6.

What percent can a conduit be filled to?

Chapter 9 Table 1 allows 53 % of the inside area for one wire, 31 % for two wires and 40 % for more than two. A nipple of 24 in. or less between boxes or enclosures may be filled to 60 % (Note 4). The ground wire counts as a wire. Table 4 gives the inside area of each conduit type and trade size, and Table 5 gives the area of each wire.

Why is the limit lower for two wires than for three?

Table 1 sets 31 % for two wires, less than the 40 % it allows for three or more. A 1/0 AWG and a 2 AWG THHN pair fills 34.9 % of 1 in. EMT and is over the 31 % limit, but with a third wire, an 8 AWG ground wire, the limit is 40 % and the same conduit passes at 39.1 %. The jam ratio is covered in the Informative Notes to Table 1 and this page does not check it.

Does the ground wire count in conduit fill?

Yes. Note 3 includes equipment grounding and bonding wires. Three 2 AWG THHN wires fit 1 in. EMT (Annex C prints 3), but with an 8 AWG ground wire in the same conduit the smallest EMT is 1-1/4 in. Use the equipment grounding conductor size calculator for the ground wire size. A bare ground wire is counted with Table 8, which this page does not include, so the page treats a bare wire as insulated and overstates its area.

What does the 0.8 rule in Note 7 mean?

When every wire in the conduit is the same size, you divide the allowed area by the area of one wire. If the decimal is 0.8 or more, you may round up to the next whole number. In 2 in. PVC Schedule 40, 1.3164 / 0.2642 = 4.98, which rounds up to 5 wires of 3/0 AWG XHHW. In Schedule 80, 2 in. gives 4.35. The decimal is under 0.8, so the count rounds down to 4, so the same five wires need 2-1/2 in. The rule is for wires of one size only.

What size conduit for 3 x 500 kcmil and a 1/0 ground?

All XHHW, in PVC Schedule 80, the answer is 3 in. The wires add up to 2.2777 sq in, and 3 in. Schedule 80 allows 2.5768 sq in at 40 %. This is a worked example in David Snyder's PDHonline course, and it is the example this page opens on. In Schedule 40 the 3 x 500 kcmil THHN, 250 kcmil and 3 AWG THHN example from Mike Holt also takes 3 in.

Can a short nipple be filled to 60 percent?

Yes, a nipple of 24 in. or less installed between boxes, cabinets or similar enclosures, under Note 4. The note also says the ampacity adjustment factors do not apply to the nipple. An RMC nipple with 6 x 4/0 AWG XHHW and two 6 AWG ground wires takes 2 in.; in a longer run it takes 3 in. Even 1/2 in. EMT holds 13 wires of 12 AWG THHN as a nipple, against 9 in a longer run.

Is conduit fill the same as the wire count I can run?

No. Fill only says the wires fit. The number of current-carrying wires also lowers the ampacity once there are more than three (310.15(C)(1)), and a long pull or many bends can call for a bigger conduit than fill alone. Use the AC wire size calculator for the wire after those adjustments.

Does this work for NM cable or other cable?

No. A multiconductor cable counts as one conductor with its actual dimensions (Notes 5 and 9), and an oval cable is measured on its longer side. This page takes single building wires in the types listed. Enter the cable dimensions by hand against the Table 4 areas.

Does this replace an electrician?

No. This page is for estimating and for checking numbers on a quote or a plan. A licensed electrician sizes and installs the raceway under a permit, and the local authority having jurisdiction inspects it.