The conduit sizing page is based on the National Electrical Code (NEC), Chapter 9, Tables 4 and 5. The page was designed for people already familiar with those tables. I wanted to build the page so the results would be exactly the same as someone doing the work by hand. One important thing to note about Table 5 is that under many of the wire types, there are only a few choices in wire size. The web page mirrors that fact, and that makes it a little more difficult to use. If you choose a wire size and nothing appears under "AREA", then you know that that size of wire isn't found under that type. If you refer to the NEC, it makes sense. I added a note in the "TYPE" column, after the colon, that shows the range of wire sizes for each type of wire. Please pay attention the warnings that appear at the top of the page and adjust your choices so the warnings disappear.

I added cable sizes, shown in inches, and fractions of an inch. The program calculates the area of each cable by the outer diameter of the cable. So, if you want to use this function. Choose the measurement closest to your cable outer diameter, the program selects "CABLE" for you. Just remember, the NEC counts one cable as one conductor for the purposes of conduit fill. See "Notes to Tables", note 9, at the beginning of NEC Chapter 9.

The tables shows bold green numbers for conduit sizes that are large enough for all the conductors that you selected in the top table and skinny red numbers for conduits that are too small. On most browsers, you can highlight individual rows to help pick the right conduit size.

If you want to use this table when you don't know exactly what type of wire you are going to pull, choose type RHH, RHW, RHW-2. That type of conductor has the thickest insulation, which just means that it takes up the most space. Use #14 for any wires smaller than #14, since #18 and #16 are not listed under RHH, RHW, RHW-2. Also, chose a "safe" multiplier, 1.15 to 1.25, to make sure you have enough spare room in your conduit. When designing new systems, I use 1.25 for my multiplier. Use the table under PVC Sch. 40 to choose your conduit size. If you do that, you are pretty well covered and you will be safely under 40% fill with just about any combination of wire and conduit.

If you have any question, please feel free to contact me. The intent of all the calculations on this website is the educate new electricians, technicians, and installers, and make the lives of those who are experienced a little easier. Feedback helps me improve these pages.