Conduit fill calculator and exam trainer
Two roads, one gate. Answer one question first: are all the wires the same size and insulation? Then it takes you down the right road, shows every step against the 40% line, and drills you with exam-style questions below.
Built on the NEC Chapter 9 method. On the Texas exam you get about 4 min 14 s per Calculations question; a conduit fill question should take you half that once the method is automatic.
Same wires or mixed?
Enter each conductor size as its own row, grounds included. Take the area of one conductor from Chapter 9, Table 5 of your book.
This is the road Annex C was built on. Work it once by hand and you can check any Annex C answer in seconds.
Use the total internal area for your raceway type and trade size from Chapter 9, Table 4. Limits from Table 1: one conductor 53%, two conductors 31%, three or more 40%.
Try it like the exam
0:00New question every time. Answer, see the working, and watch your streak.
Ready for the whole Calculations portion?
Conduit fill is one of the question types on the Texas Calculations portion. Our free 20-question diagnostic covers all of them on the 2026 NEC and shows which areas cost you points.
Take the free diagnostic See the full exam packMore free trainers: Voltage drop trainer · Amps, kW and kVA trainer · Box fill trainer