How to use this calculator
- Enter Conduit (EMT).
- Enter Wire (THHN).
- Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.
Formula & constants
NEC caps fill at 40% of conduit area for 3+ wires. Typical THHN capacity: 1/2 in EMT holds 9 × 12 AWG; 3/4 in holds 16 × 12 AWG; 1 in holds 26 × 12 AWG. Every default in the fields above is editable — when your supplier’s spec sheet lists a different density, coverage rate or price, enter that number instead. The waste and compaction allowances follow common trade practice; see our methodology page for the derivation of each formula and the standards it references.
Where this fits in the project
Electrical sizing works backwards from load: total demand sets service size, circuit amperage sets wire gauge, and conductor count sets conduit fill. HVAC equipment is sized from the BTU load, never from floor area alone.
How this connects to your project
No quantity stands alone — each material in the chain depends on the ones around it. These are the planning steps that pair with the conduit fill calculator:
- Wire Size Calculator — Conduit carries electrical wires of specific gauges.
- Electrical Load Calculator — Circuit design affects how many wires share conduit.
- Recessed Lighting Calculator — Lighting circuits run through conduit.
Frequently asked questions
Why only 40% fill?
Heat dissipation and pull-friction — overstuffed conduit overheats conductors and makes pulls damage insulation.
Do grounds count toward fill?
Yes — every conductor including the equipment ground counts in the fill calculation.
Last verified: — prices reflect current national averages. See our methodology.
Estimates are for planning. Material densities, coverage rates and prices vary by region and supplier — confirm final quantities before ordering, and check local code where structural or electrical work is involved.