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🚇 Conduit Fill

How big a conduit do you need for your wires? Enter what you're pulling, get the smallest legal size.

EMT is the common thin-wall metal tubing. PVC Sch 40 is the gray plastic conduit.

Wire size (THHN / THWN) Quantity

Sizes are for standard THHN/THWN insulated building wire — the most common single-conductor wire pulled in conduit.

Count every insulated wire in the pipe, including the neutral and an insulated ground. Use a separate row for each size.

The fill rules, in plain English

Wires need free space in a conduit — jam it full and you can't pull them through, and they can overheat. The standard U.S. limits (NEC Chapter 9): one wire may fill 53% of the pipe's inside area, two wires 31%, and three or more 40%. We do that area math for you using the official wire and conduit dimensions.

Good to know: long runs with lots of bends are easier with a size bigger than the legal minimum — many electricians upsize on purpose.

Want to know why you should trust this result? Read how VoltDrop checks its numbers.