300 kcmil Conduit Fill by Conduit Size
How many 300 kcmil THHN conductors fit in EMT, IMC, RMC and PVC conduit, 1/2 inch through 4 inch, with the 40% fill rule applied.
Quick answer
300 kcmil conductors per conduit trade size
Same-size conductors only, at 53% for one, 31% for two and 40% for three or more.
| Conduit | 1/2" | 3/4" | 1" | 1-1/4" | 1-1/2" | 2" | 2-1/2" | 3" | 3-1/2" | 4" |
|---|---|---|---|---|---|---|---|---|---|---|
| EMT | — | — | — | 1 | 1 | 2 | 5 | 7 | 10 | 12 |
| IMC | — | — | 1 | 1 | 1 | 3 | 4 | 6 | 9 | 11 |
| RMC | — | — | 1 | 1 | 1 | 2 | 4 | 6 | 8 | 11 |
| PVC Sch 40 | — | — | — | 1 | 1 | 2 | 4 | 6 | 8 | 10 |
| PVC Sch 80 | — | — | — | 1 | 1 | 1 | 3 | 5 | 7 | 9 |
Source & method: Counts are the largest whole number where n × conductor area stays inside the raceway area times the applicable fill percentage. Mix conductor sizes in the calculator.
Fill behaviour at 300 kcmil: bend radius drives the design
300 kcmil conductors are stiff enough that minimum bending radius, sweep selection and pull box placement dominate the layout. The fill counts above set the floor, but almost no 300 kcmil raceway is installed at that floor.
A common design pattern at this size is one conductor per raceway or per tray position for very long runs, which removes fill from the equation entirely and replaces it with support spacing, thermal considerations and, in metal raceway, induced-current concerns when a single conductor of an alternating-current circuit is isolated in ferrous conduit.
Source & method: Counts referenced above come from the computed table on this page — how these numbers are derived.
What each raceway type means
- EMT — EMT (electrical metallic tubing)
- IMC — IMC (intermediate metal conduit)
- RMC — RMC (rigid metal conduit)
- PVC Sch 40 — PVC Schedule 40
- PVC Sch 80 — PVC Schedule 80
Full fill charts by raceway
Per-type counts for every trade size, plus the cross-type comparison and reverse lookup.
- EMT conduit fill chart — 1/2" to 4"Electrical metallic tubing, thinnest wall, highest count per trade size.
- Conduit fill chart — all raceway types comparedEMT, IMC, RMC, PVC 40 and PVC 80 side by side with reverse lookup.
- PVC conduit fill chart — Schedule 40 and 80Thicker walls, roughly 15 to 25% fewer conductors than tubing.
- Rigid conduit fill chart — RMC and IMCThreaded metal raceway counts and usable areas.
Frequently asked
- How many 300 kcmil wires fit in 1/2 inch EMT?
- None — this size does not fit 1/2 inch EMT; step up a trade size.
- How many 300 kcmil wires fit in 3/4 inch EMT?
- 0 conductors, using a nominal THHN outside diameter of 0.766 in and the 40% fill rule for three or more conductors.
- Do neutrals and grounds count toward fill?
- Yes, every conductor in the raceway counts for fill. Grounds are excluded only from the count of current-carrying conductors used for ampacity adjustment.
- What is the cross-sectional area of 300 kcmil THHN?
- About 0.4608 square inches, from A = π × (OD / 2)² with a nominal insulated OD of 0.766 in.
More on 300 kcmil
Conduit fill for nearby sizes
Same 40% fill rule applied to the sizes either side of this one, wrapping around the range so every size is reachable.
Related charts & calculators
- Allen Wrench Size ChartHex key sizes with SAE and metric cross-reference.
- Voltage Drop CalculatorPercent drop, end voltage and minimum conductor for any run length.
- Conduit Fill CalculatorFill percentage and maximum conductor count for EMT, RMC, IMC and PVC.
- Breaker Size CalculatorOvercurrent device rating and minimum conductor from load current.
- Wire Ampacity CalculatorDerated ampacity for ambient temperature and bundled conductors.
- Box Fill CalculatorVolume allowances for conductors, clamps, devices and grounds per NEC 314.16.