WeekendCalc

Conduit Fill Calculator: How Many Wires Fit in EMT or PVC

Choose the conduit, the wire size and how many wires you are pulling. You get the percent fill against the NEC limit, the most wires of that size the conduit holds, and the smallest conduit that fits.

Jump to your result ↓

Your project

Results

Example job shown. Change the numbers to match yours.

Conduit fill
17.5 %
The limit is 40% for 7 wires
Within the NEC limit?Fits in 3/4 in EMT
Yes
Most 12 AWG wires this conduit holdsNot counting the ground wire
15 wires
Smallest EMT that fits your wiresTrade size 1/2 in
0.50 in
Total area of the wires
0.093 in²
Area allowed in this conduitAt 40% of 0.533 in²
0.213 in²
  • This follows NEC Chapter 9: Table 1 (53% fill for one wire, 31% for two, 40% for three or more), Table 4 (the inside area of the conduit) and Table 5 (the area of THHN and THWN-2 wire). It does not apply to NM-B (Romex) cable, and other insulation types such as XHHW have different areas.
  • More than three current-carrying wires in one conduit lower the ampacity of every wire (adjustment factors in NEC 310.15), so a conduit that is physically big enough may still need larger wire. Keep bends to 360 degrees between pull points.
  • Conduit nipples of 24 inches or less may be filled to 60%. Your local code and inspector decide what is acceptable.

Before you buy: round up to whole packs, check the size printed on the label, and add a little spare. Your supplier has the final say.

How this calculator works

The National Electrical Code limits how much of a conduit's inside area the wires may fill, so that they can be pulled and do not overheat. One wire may fill 53% of the area, two wires 31%, and three or more 40%. The area of each wire (with its insulation) comes from Chapter 9, Table 5, and the inside area of each conduit size from Table 4. Add up the wire areas and divide by the conduit area to get the percent fill.

fill % = (number of wires × area of one wire) ÷ inside area of the conduit × 100 must not exceed 40% for three or more wires

Worked example: six 12 AWG THHN wires and a 12 AWG ground in 3/4 inch EMT are seven wires of 0.0133 in², a total of 0.0931 in², in a conduit of 0.533 in². That is 17.5% fill, well inside the 40% limit, and the conduit would hold up to 16 wires of that size in all. A 1/2 inch EMT holds 9 of them, a 3/4 inch EMT 16, a 1 inch EMT 26 and a 3/4 inch PVC Schedule 40 conduit 15. Nine 12 AWG wires and a ground make 25.0% in the 3/4 inch conduit. Ten wires of 12 AWG are over the limit for a 1/2 inch EMT (43.8% fill), and the smallest EMT for them is 3/4 inch.

Most THHN wires in EMT (a wire count with no separate ground)

The same numbers as the NEC Annex C chart, worked out by this calculator.

Wire1/2 in3/4 in1 in1-1/4 in1-1/2 in2 in
14 AWG1222356184138
12 AWG916264561101
10 AWG51016283863
8 AWG369162236
6 AWG247121626
4 AWG12471016

Tips before you buy

  • Count every wire you pull: each hot, each neutral and each ground. A ground wire takes up room too, so count it as well.
  • Pulling gets harder well before the code limit. For a long run or several bends, stay near 30% fill or go up a size.
  • Choose the next size up when you may add circuits later: conduit is cheap compared with opening a wall to replace it.
  • Use THHN or THWN-2 wire in the conduit. Romex (NM-B) cable is for inside walls and is not pulled through conduit as a fill problem.
  • More wires per conduit means more heat, so check the ampacity adjustment for more than three current-carrying wires.

Tools & materials for this project

Affiliate links As an Amazon Associate we earn from qualifying purchases. These links do not change what you pay.

EMT conduit 10 ftTHHN wire 12 AWGWire fish tapeWire pulling lubricantEMT bender

Frequently asked questions

How many 12 gauge wires fit in 1/2 inch conduit?

9 wires of 12 AWG THHN fit in 1/2 inch EMT, 16 in 3/4 inch EMT and 26 in 1 inch EMT. The ground wire counts too.

How many 10 gauge wires fit in 3/4 inch conduit?

10 wires of 10 AWG THHN fit in 3/4 inch EMT. In 3/4 inch PVC Schedule 40 it is 9.

What is the maximum conduit fill?

The NEC allows 40% for three or more wires, 31% for two wires and 53% for one wire. Short conduit nipples of 24 inches or less may be filled to 60%.

Does the ground wire count in conduit fill?

Yes: every conductor in the conduit counts, including the ground. Seven wires of 12 AWG (six plus a ground) are 17.5% of a 3/4 inch EMT.

Why does 8 AWG fit one more wire than the 40% area suggests?

When all the wires are the same size and the fit comes to 0.8 or more of the next whole number, the code lets you round up. 3/4 inch EMT holds 6 wires of 8 AWG that way, as the Annex C chart shows.

Add this calculator to your website

Running a blog, a contractor site or a class page? You can put this calculator on it for free. Copy the code below, and please leave the link underneath the calculator in place. The small script just resizes the frame to fit the results; if your site strips scripts, the calculator still works inside a scrolling frame.

Get the embed code

Related calculators & guides

Wire Size Calculator (AWG for Amps and Distance)The smallest copper or aluminum wire for a load in amps, and for a 3% voltage drop.Breaker Size CalculatorThe circuit breaker size for a load in amps or watts, and the wire to match.Voltage Drop CalculatorVoltage drop in a wire run, and the smallest wire for 3% or less.Circuit Capacity Calculator: How Many Watts?How many watts a 15, 20, 30 or 50 amp circuit can handle, and how many appliances.How Many Wires Fit in Conduit? EMT and PVC Fill ChartGuidePlanner: Sizing a circuit: watts, amps, wire and breakerLoad, current, breaker, wire size, voltage drop and capacity

Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.