Conduit Fill Calculator
NEC Chapter 9 Table 1 limits conduit fill to 53% for one conductor, 31% for two, and 40% for three or more. Enter conduit type/size and wire gauge/count to get fill percentage and whether your installation is NEC-compliant.
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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.