Conduit Fill Calculator
Find the smallest raceway that fits your conductors per NEC Chapter 9. Mix insulation types and sizes, and the calculator applies the right fill percentage, shows the areas it used and flags jam-ratio risk.
Take this math to the job site.
The JobVolt app runs the same verified engines offline, keeps every calculation in History, and turns them into inspector-ready PDF submittals on your letterhead.
How conduit fill works
Conductor areas come from Chapter 9 Table 5, raceway areas from Table 4, and the allowed fill percentage from Table 1: 53% for one conductor, 31% for two, 40% for three or more, and 60% for nipples 24 inches or shorter per Note 4. The calculator walks trade sizes from 1/2 inch up and returns the first one that fits.
What is the jam ratio?
When exactly three conductors go around a bend, they can line up side by side and wedge if the conduit inner diameter divided by the conductor diameter lands near 3.0. The calculator checks Chapter 9 Note 7 territory and warns you, so you can bump the trade size before the pull fights back.
Prefer the raw numbers? The conduit fill chart is on the site too, rendered from the same verified dataset this calculator reads.