Formula and method
Conduit area = π × inside diameter² ÷ 4. Occupied area = sum of each conductor-group quantity × π × outside diameter² ÷ 4. Fill percentage = occupied area ÷ conduit area × 100.
Worked example
With a 1 in conduit inside diameter and three conductors each 0.2 in outside diameter, occupied area is 0.09425 in², conduit area is 0.78540 in², and fill is 12%. The three-conductor Table 1 reference band is 40%.
Assumptions
The NFPA 70 Chapter 9 Table 1 reference shown is 53% for one, 31% for two, and 40% for more than two conductors; exceptions and adopted editions vary. The calculator uses your measured or manufacturer-specified diameters and does not supply nominal-size tables.
Important limitations
Not a code, inspection, electrical-safety, ampacity, derating, voltage-drop, grounding, breaker, or installation approval. Verify the current adopted code, conductor and raceway specifications, local requirements, and project conditions with a qualified professional.
Frequently asked questions
Does nominal conduit size equal inside diameter? No. Use the actual inside diameter for the exact raceway. Do grounding or bonding conductors count? The referenced NFPA table notes include them; this tool does not identify or classify conductors for you.
Privacy
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