Box Fill Calculator

Check a device or junction box against NEC 314.16. Enter the conductors, devices, clamps, support fittings, and grounds, and the calculator totals the required cubic-inch volume and compares it to your box — with the largest conductor count that fits.

Box & Contents

Box Type (314.16(A))

Box Volume (in³)

Or enter the stamped volume

Conductors (B)(1)

Devices (recept./switch)

2× largest conductor

Support Fittings

1× largest each

Clamps

EGC Size

# EGCs

All = 1×

Box Fill — NEC 314.16

Required Volume22.5 in³

Box Volume18 in³

Spare Volume-4.5 in³

✗ Over fill — use a larger box or fewer conductors

NEC 314.16(A) box volumes; 314.16(B) allowances — each conductor at its own size, devices 2× / clamps & fittings 1× the largest conductor, all EGCs = 1×.

Method: per-conductor volume allowances from NEC Table 314.16(B). Each device (receptacle/switch) counts as two conductors; all internal clamps together count once; each support fitting counts once; all grounding conductors together count once. Verify against the governing NEC edition.

Run your whole job on the same numbers

These NORDIX tools are a taste of the full platform — bid pipeline, estimating, and job costing that carry your numbers from the first bid to the final invoice.

See what NORDIX does →