Free Calculator
Conduit Fill Calculator & Wire Fill Chart
Check percent conduit fill against the NEC Chapter 9 limits — enter your conductors and raceway, and get the fill percentage, a pass or fail against the 53% / 31% / 40% rule, and the smallest trade size that will take the pull.
Built by SubcontractorHub — the software electrical contractors use to quote, finance, and run every job.
Book a DemoCheck Your Conduit Fill in Seconds
Pick the raceway, add each group of conductors, and see percent fill, the applicable NEC limit, and the minimum conduit size that works.
Internal area: 0.533 sq in
Conductors in the raceway
Add each group of conductors — phases, neutral, and the equipment grounding conductor all count. Set a quantity to 0 to skip a row.
📋 Important: All calculator results are ballpark estimates
The figures shown are approximate estimates based on the published NEC Chapter 9 tables and should be used for general planning purposes only. They are not a substitute for the National Electrical Code, local amendments, or a professional electrical design. Actual raceway sizing varies with manufacturer jacket dimensions, bare grounding conductors, nipple lengths, and conductors already occupying the raceway. Always confirm conduit sizing with a licensed electrician before purchasing, permitting, or installing.
How NEC Conduit Fill Works
The fill limit depends on how many conductors you pull
Most electricians know the “40% rule,” but NEC Chapter 9, Table 1 actually sets three different limits, and the middle one catches people out. Two conductors are held to a stricter limit than three or more, because two round conductors waste more space inside a round raceway than a tighter bundle does.
| Number of conductors | Maximum fill |
|---|---|
| 1 conductor | 53% |
| 2 conductors | 31% |
| 3 or more conductors | 40% |
| Nipple, 24 in. or shorter | 60% |
Percent fill is always calculated against the conduit's total internal area from Table 4 — you do not derate the conduit area first and then compare.
Insulation type changes the answer as much as wire size
Conductor area comes from Chapter 9, Table 5, and it is the area including insulation. The same 12 AWG copper occupies 0.0133 sq in as THHN but 0.0260 sq in as THW — nearly double. Sizing a raceway from wire gauge alone, without checking the insulation, is one of the most common ways a pull fails inspection.
| Conductor | THHN / THWN-2 | XHHW | THW |
|---|---|---|---|
| 14 AWG | 0.0097 | 0.0139 | 0.0209 |
| 12 AWG | 0.0133 | 0.0181 | 0.0260 |
| 10 AWG | 0.0211 | 0.0243 | 0.0333 |
| 8 AWG | 0.0366 | 0.0437 | 0.0556 |
| 6 AWG | 0.0507 | 0.0590 | 0.0726 |
| 4 AWG | 0.0824 | 0.0814 | 0.0973 |
Areas in square inches, NEC Chapter 9, Table 5.
Trade size is not internal diameter
A 1-inch raceway does not hold 1 inch of anything. Trade size is a nominal label, and the usable area behind it swings by roughly 20% across conduit types. That is why a design that passes in EMT can fail after a field change to Schedule 80 PVC.
| Trade size | EMT | RMC | PVC 40 | PVC 80 |
|---|---|---|---|---|
| 1/2" | 0.304 | 0.314 | 0.285 | 0.217 |
| 3/4" | 0.533 | 0.549 | 0.508 | 0.409 |
| 1" | 0.864 | 0.887 | 0.832 | 0.688 |
| 1-1/4" | 1.496 | 1.526 | 1.453 | 1.237 |
| 1-1/2" | 2.036 | 2.071 | 1.986 | 1.711 |
| 2" | 3.356 | 3.408 | 3.291 | 2.874 |
Total internal area in square inches, NEC Chapter 9, Table 4.
Conduit fill chart: how many wires fit in 1/2 inch, 3/4 inch and larger conduit
The question that comes up on nearly every rough-in is some version of “how many 12 AWG THHN fit in 3/4 EMT?” This conduit fill chart answers it directly for a uniform pull — every conductor the same size and insulation. Read down to your wire size, across to the trade size, and the cell is the maximum conductor count. For mixed conductor sizes, use the calculator above instead, because a mixed bundle is judged on total area rather than on these tables.
EMT — THHN / THWN-2 conductors
| Wire size | 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 | — | 1 | 1 | 3 | 4 | 7 |
| 2/0 AWG | — | 1 | 1 | 2 | 3 | 6 |
| 3/0 AWG | — | 1 | 1 | 1 | 3 | 5 |
| 4/0 AWG | — | — | 1 | 1 | 1 | 4 |
Read the common pulls straight off the chart: nine 12 AWG THHN fit in 1/2 inch EMT, sixteen fit in 3/4 inch EMT, and twenty-six fit in 1 inch EMT. Ten 10 AWG THHN fit in 3/4 inch EMT, and six 8 AWG fit the same raceway. A single 4/0 conductor needs at least 1 inch EMT.
PVC Schedule 40 — THHN / THWN-2 conductors
| Wire size | 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 | — | 1 | 1 | 3 | 5 | 8 |
| 1/0 AWG | — | 1 | 1 | 3 | 4 | 7 |
| 2/0 AWG | — | 1 | 1 | 2 | 3 | 6 |
| 3/0 AWG | — | 1 | 1 | 1 | 3 | 5 |
| 4/0 AWG | — | — | 1 | 1 | 1 | 4 |
Counts are computed at the 40% limit from the NEC Chapter 9, Table 4 and Table 5 figures shown above, with the Note 7 rounding allowance applied to uniform bundles — which is what reproduces the published NEC Annex C, Table C.1 and C.10 values. Where only one or two conductors fit, the stricter 53% and 31% limits govern instead, which is why 6 AWG shows one conductor in 1/2 inch EMT rather than two. Schedule 80 PVC, IMC, RMC and flexible conduit (FMC) have different internal areas — select them in the calculator above for an exact count. Verify against the NEC and your local amendments before permitting.
Conduit fill by trade size: 1/2 inch, 3/4 inch, 1 inch and 1 1/4 inch
On site the question is almost never phrased as a fill percentage. It is “what is the 3/4 EMT conduit fill for 12 THHN” or “how many wires in 1/2 inch conduit”. These are the answers for the pulls that come up most, taken from the charts above at the 40% limit for three or more current-carrying conductors.
1/2 inch conduit fill
1/2 inch EMT conduit fill: twelve 14 AWG THHN, nine 12 AWG, five 10 AWG, three 8 AWG, or one 6 AWG. 1/2 inch PVC Schedule 40: eleven 14 AWG, eight 12 AWG, five 10 AWG, three 8 AWG. Half inch is the smallest trade size in general use, and a 1/2 inch raceway runs out of room faster than people expect once 10 AWG or larger is involved — three 8 AWG conductors is the practical ceiling.
3/4 inch conduit fill
3/4 inch EMT conduit fill: twenty-two 14 AWG THHN, sixteen 12 AWG, ten 10 AWG, six 8 AWG, or four 6 AWG. 3/4 inch PVC Schedule 40: twenty-one 14 AWG, fifteen 12 AWG, nine 10 AWG, five 8 AWG, four 6 AWG. Three quarter inch EMT carrying sixteen 12 AWG is the single most common residential and light commercial branch-circuit pull in the country, which is why it is worth knowing without looking it up.
1 inch conduit fill
1 inch EMT conduit fill: thirty-five 14 AWG THHN, twenty-six 12 AWG, sixteen 10 AWG, nine 8 AWG, seven 6 AWG, or four 4 AWG. 1 inch PVC Schedule 40: thirty-four 14 AWG, twenty-five 12 AWG, fifteen 10 AWG, nine 8 AWG, six 6 AWG.
1 1/4 inch conduit fill
1 1/4 inch EMT conduit fill: sixty-one 14 AWG THHN, forty-five 12 AWG, twenty-eight 10 AWG, sixteen 8 AWG, twelve 6 AWG, or seven 4 AWG. 1 1/4 inch PVC conduit fill chart: sixty 14 AWG, forty-three 12 AWG, twenty-seven 10 AWG, sixteen 8 AWG, eleven 6 AWG, seven 4 AWG. One and a quarter inch is usually where a feeder rather than a branch circuit starts, so the governing figure is more often the large-conductor row than the count of small ones.
Does conduit type change the answer?
Yes, and the order is consistent. At any given trade size, IMC has the most usable area, then RMC, then EMT, then PVC Schedule 40, with PVC Schedule 80 the most restrictive because its thicker wall eats the bore — Schedule 80 in 1/2 inch has roughly 24% less internal area than RMC in the same trade size. That is why a pull that passes in 3/4 inch EMT can fail in 3/4 inch Schedule 80. Switch the conduit type in the calculator above rather than assuming the trade size carries across. Flexible conduit (FMC, and liquidtight LFMC) has its own Table 4 areas that differ again, and is not currently covered by this calculator — size those pulls from the NEC table directly.
Passing fill does not mean passing inspection
Conduit fill and conductor ampacity are two separate tests, and a pull can clear one while failing the other. Once a raceway carries more than three current-carrying conductors, NEC 310.15(C)(1) requires an ampacity adjustment: 80% for 4 to 6 conductors, 70% for 7 to 9, and 50% for 10 to 20. Bundle enough circuits into one conduit and the wire that fit comfortably is no longer large enough for its breaker.
Check fill here, then size the conductors themselves with the wire size calculator and confirm the run length with the voltage drop calculator.
Why estimators care about fill, not just installers
Conduit size drives material cost, fitting count, labor units, and hanger spacing. Discovering during rough-in that a run needs to step from 3/4" to 1" is a change order at best and absorbed margin at worst. Estimators who check fill during takeoff — rather than after the bid is submitted — protect the number they quoted. That is the same reason it pays to keep takeoff, proposal, and job costing in one system: see how electrical contractor software connects the estimate to the job it becomes.
From Load Calculations to a Signed Proposal
SubcontractorHub helps electrical contractors build accurate estimates, send professional proposals, collect deposits, and manage jobs from lead to payment.
Book a Free DemoFrequently Asked Questions
What is the maximum conduit fill allowed by the NEC?
NEC Chapter 9, Table 1 sets the limit by how many conductors are in the raceway: 53% for a single conductor, 31% for exactly two conductors, and 40% for three or more. The two-conductor case is the one people get wrong — it is stricter than the three-or-more case, because two round conductors pack inefficiently inside a round raceway. The calculator applies the correct limit automatically based on the total conductor count you enter.
How do you calculate conduit fill?
Add up the cross-sectional area of every conductor (NEC Chapter 9, Table 5, which varies by insulation type), then divide by the total internal area of the conduit (Table 4, which varies by conduit type and trade size). Multiply by 100 to get percent fill, and compare that against the Table 1 limit for your conductor count. Note that fill is calculated on the conduit's TOTAL internal area, not on the already-derated allowable area.
Does the equipment grounding conductor count toward conduit fill?
Yes. Every conductor in the raceway counts toward fill, including the equipment grounding conductor and the neutral, whether insulated or bare. A bare ground uses the bare-conductor dimensions from Chapter 9, Table 8 rather than Table 5. Add the ground as its own row in the calculator so it is included in both the area total and the conductor count that selects the fill limit.
Why does the same wire fill EMT and PVC differently?
Trade size names the nominal size, not the internal diameter. A 1-inch EMT has 0.864 sq in of internal area while 1-inch PVC Schedule 80 has only 0.688 sq in — about 20% less room — because Schedule 80 has thicker walls. Swapping conduit type late in a job is a common way to turn a compliant pull into a violation, so re-check fill any time the raceway type changes.
Do I have to derate conductors when a conduit has more than three current-carrying wires?
Yes, and it is a separate requirement from fill. NEC 310.15(C)(1) requires an ampacity adjustment once a raceway holds more than three current-carrying conductors — 80% for 4 to 6, 70% for 7 to 9, and 50% for 10 to 20. A pull can pass conduit fill and still fail because the conductors are no longer large enough after derating. Check fill and ampacity adjustment separately.
What is the 40% conduit fill rule?
It is the most commonly cited limit because most real pulls contain three or more conductors, which caps fill at 40% of the conduit's internal area. It exists to leave room for heat dissipation and to keep pulling tension low enough that insulation is not damaged during installation. It is a maximum, not a target — many contractors design to roughly 30% to leave room for future adds.
Why do the NEC Annex C tables sometimes allow one more conductor than 40% appears to?
Because of Note 7 to NEC Chapter 9. Where every conductor in the raceway is the same size, the next higher whole number of conductors is permitted when the fill calculation results in a decimal of 0.80 or larger. That is why Annex C lists 26 conductors of 12 AWG THHN in 1-inch EMT even though 26 conductors work out marginally above 40% by raw area. The allowance applies only to a uniform bundle — a pull with mixed conductor sizes is judged on total area alone. This calculator applies Note 7 automatically when every conductor you enter is the same size and insulation, and tells you when it did.
How many 12 AWG THHN wires fit in 3/4 inch EMT?
Sixteen. A 3/4 inch EMT raceway has 0.533 square inches of total internal area, and the 40% limit that applies to three or more conductors leaves 0.213 square inches. At 0.0133 square inches each, sixteen 12 AWG THHN conductors fit. The same raceway takes twenty-two 14 AWG, ten 10 AWG, six 8 AWG, or four 6 AWG THHN. Remember that every conductor counts, including the neutral and the equipment grounding conductor, so a four-wire circuit with a ground uses five of those sixteen slots.
How many wires can you put in 1/2 inch conduit?
In 1/2 inch EMT, twelve 14 AWG THHN, nine 12 AWG, five 10 AWG, or three 8 AWG conductors. In 1/2 inch PVC Schedule 40 the counts drop slightly to eleven, eight, five and three, because PVC has thicker walls and less usable internal area for the same trade size. At 6 AWG only one conductor is permitted in 1/2 inch conduit, not two, because a two-conductor pull is held to the stricter 31% limit rather than 40%.
What size conduit do I need for 4/0 wire?
A single 4/0 THHN conductor needs at least 1 inch conduit, and three 4/0 conductors need 2 inch EMT or PVC. Because a 4/0 THHN conductor is 0.3237 square inches, the usual 200 amp service pull of three 4/0 conductors plus a grounded conductor will generally land at 2 inch or larger once the neutral and ground are counted. Enter the exact conductor mix in the calculator above rather than sizing from the chart, since service pulls are rarely a uniform bundle.
Is there a conduit fill chart for PVC and flex conduit?
The chart on this page covers EMT and PVC Schedule 40, which are the two raceways most commonly asked about. Schedule 80 PVC, IMC, RMC and flexible metal conduit (FMC) each have different internal areas for the same trade size, so their conductor counts differ, and Schedule 80 in particular is noticeably tighter than Schedule 40. Select the conduit type in the calculator above to get the count for those raceways, and confirm against NEC Chapter 9, Annex C before ordering material.
Win More Electrical Jobs
Send professional proposals, collect digital signatures, and track every job in one platform built for electrical contractors.
Get a Free DemoAll calculations are ballpark estimates based on the published NEC Chapter 9 tables and should be verified against the National Electrical Code, local amendments, and a licensed electrician in your area before making any purchasing or installation decisions. All calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements.