THHN/THWN-2 conductors — mix up to four sizes — in EMT or PVC Schedule 40, checked against the NEC Chapter 9 fill limits. The meter shows your fill percentage and names the smallest conduit that legally fits the pull.
Part of The Talking Toolbox. The meter generates the pull; you name the pipe. Endless problems, graded on the spot — five straight and the trade is yours.
Press New Problem to start the drill.
Streak: 0 · Best: 0
The NEC doesn't let you stuff a pipe. Chapter 9, Table 1 limits how much of a conduit's cross-section your conductors may occupy: 53% for one conductor, 31% for two, and 40% for three or more. The two-wire limit is the strictest because a pair lies side by side and binds on bends; three or more nest and pull cleaner.
With mixed sizes, you total the actual areas of every conductor and compare against the allowance — no shortcuts. Overfilled conduit means scraped insulation, brutal pulls, and a failed inspection. Undersized by one trade size is the most common rookie mistake on rough-in.
One conductor: 53%. Two conductors: 31%. Three or more: 40%. Nipples 24 inches or shorter are allowed 60%. These come from NEC Chapter 9, Table 1 and its notes.
Two conductors ride side by side and wedge against each other in bends. Three or more settle into a bundle that pulls more predictably, so the code gives them more room.
Yes — total the actual cross-sectional areas of every conductor and compare against the allowed percentage. That is exactly the arithmetic this tool performs.
No. It uses standard published THHN/THWN-2 and conduit dimensions for estimating. Verify against the current NEC Chapter 9 tables, local amendments, and your inspector before installing.
Job-Site Math: The Sovereign Tradesman's Field Companion by Dr. Gene A. Constant teaches this exact math — the fill limits, the mixed-size method, worked pulls, and a full answer key — for $3.99 on Kindle. And GENO, the GSU AI tutor, has memorized the entire book: he'll talk you through any chapter out loud, 24/7, in 83 languages.
Get Job-Site Math — $3.99 Ask GENO to Explain ItEducational tool provided free by Global Sovereign University, a program of The Foundation for Global Instruction (501(c)(3)). Areas are standard published dimensions for THHN/THWN-2, EMT, and PVC Schedule 40; other insulations and raceways differ. Verify every result against the current NEC Chapter 9 tables, local amendments, and a licensed electrician or inspector. When in doubt, hire a professional.