NEC Electrical Box Fill Calculator
Box fill is a volume allowance check. The working calculator totals insulated conductors, grounds, device yokes, clamps and fittings against the marked box volume.
electrical box fill calculator nec nec box fill calculator junction box fill calculator
Required volume
Vreq = Vconductors + Vgrounds + Vyokes + Vclamps + Vsupports
Fill percent
fill_percent = 100 * Vreq / Vbox
Code caution
The calculator is an arithmetic screen for common conductor sizes. Pull boxes, conduit bodies, special devices and local amendments need adopted-code review.
Related pages
- Transformer kVA calculator - load kVA, design margin and standard size rounding.
- Conduit fill calculator - raceway fill from conductor count, area and conduit size.
- Voltage drop calculator - feeder voltage drop and conductor-size screening.
- Short-circuit current calculator - available fault current from transformer impedance.