Conduit Fill Calculator

Inputs

Conductor groups

Use one group for same-size conductors, or add second/third groups for mixed wire sizes.

Primary conductor

Conductor insulation type and size. Fill uses the outside area of the insulated conductor, not bare copper area.

Primary count (N)

Count each conductor occupying conduit area. Mixed sizes should be summed separately; this calculator screens same-size conductors.

Conduit

Conduit type and trade size. Use the exact internal area for the raceway actually being installed.

Fill rule

Standard raceway fill uses conductor-count limits. Short nipples can use the 60% screen when the code condition applies.

Default result

Conduit fill(F)

22.5%

Pass

3/4 EMT (0.533 in²) passes for 9 conductors.

Also computed

Fill limit40%

three-or-more conductor rule

Max primary-size conductors16conductors

if all conductors are #12 THHN/THWN-2

Conductor area total77.23mm²

Allowable area137.5mm²

Remaining fill area60.32mm²

Method notes 3 notes

Groups included: 9 x #12 THHN/THWN-2. Selected conduit internal area: 0.533 in².
For mixed conductor sizes, fill is based on the summed insulation area. The maximum primary-size conductor output is a same-size reference only.
Conduit fill is not ampacity adjustment, box fill, bend radius, pulling tension or equipment-grounding-conductor sizing. Verify final work against the adopted NEC edition, local amendments and manufacturer dimensions.