Conduit Fill Calculator
NEC Chapter 9 Table 1 limits conduit fill to prevent overheating and to allow conductors to be pulled and removed without damage. The limits are 53% for one conductor, 31% for two conductors, and 40% for three or more. This calculator uses NEC Table 4 (conduit internal area by type and size) and Table 5 (THHN conductor area by AWG) to compute fill percentage for EMT, Schedule 40 PVC, or Rigid Metal Conduit. Enter conduit type, trade size, wire gauge, and conductor count to get fill percentage, NEC compliance status, maximum number of conductors of that gauge that fit, and the next conduit size up if your configuration is over-filled. PVC conduit has slightly smaller internal area than EMT of the same trade size.
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How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
What is the maximum conduit fill per NEC?
NEC Table 1, Chapter 9: 53% for 1 conductor, 31% for 2 conductors, and 40% for 3 or more conductors. These percentages apply to the internal cross-sectional area of the conduit. Exceeding fill limits makes wire pulling difficult and generates excessive heat.
How many 12 AWG wires fit in 3/4" EMT conduit?
A 3/4" EMT conduit has an internal area of 0.533 sq in. At 40% fill (3+ conductors), the allowed area is 0.213 sq in. Each 12 AWG THHN wire occupies 0.0133 sq in, so you can fit floor(0.213 / 0.0133) = 16 conductors maximum.
What is the difference between EMT, PVC, and Rigid conduit?
EMT (Electrical Metallic Tubing) is thin-wall steel — lightweight, easy to cut and bend, and the most common choice for interior commercial and residential wiring. PVC Schedule 40 conduit is plastic — used underground, in wet locations, and where corrosion resistance is needed. Rigid Metal Conduit (RMC) is heavy-wall steel — used in industrial settings and where maximum protection is required. EMT has slightly more interior area than PVC of the same trade size.
Does the ground wire count toward conduit fill?
Yes — all conductors including the equipment grounding conductor (EGC) count toward conduit fill. Count every wire including the bare copper ground when calculating fill. For a typical 20A 120V circuit in conduit, you have 3 conductors: hot, neutral, and ground.