Conduit Fill Calculator
Your estimate
Conduit fill14.97%
Max wires of this size16
- Allowed fill
- 40%
- Code check
- OK
EMT or PVC Schedule 40 with THHN/THWN-2 wires — percent fill and how many wires fit.
Updated 2026-10-20 · Based on: NEC Chapter 9 Table 8 and 310.16; DIN VDE 0100-520 for metric.
How to use the Conduit Fill Calculator
- Choose the conduit type and trade size.
- Choose the wire size and count.
- Stay at or under 40 % fill for three or more wires.
Formula
Fill = total wire area ÷ conduit internal area (NEC Chapter 9, Tables 4 and 5).
Limits: 53 % for one wire, 31 % for two, 40 % for three or more.
Worked example
With the values preset in the calculator above:
- Conduit type
- EMT
- Trade size
- 3/4
- Wire size (THHN)
- 12
- Number of wires
- 6
- Conduit fill
- 14.97%
- Allowed fill
- 40%
- Max wires of this size
- 16
- Code check
- OK
Related guides
Frequently asked questions
How many 12 AWG wires in ¾ EMT?
16 THHN conductors at 40 % fill.
How many 10 AWG in ½ EMT?
5 THHN conductors.
Do ground wires count toward fill?
Yes — every conductor, including equipment grounds, counts.
More calculators
Estimates only — check quantities with your supplier and local building code before you order.