Disclaimer: RacewayIQ is an informational engineering tool only. All calculations must be independently verified by the user. Do not rely on these results as the sole basis for design, procurement, installation, construction, permitting, or code compliance decisions.

Box Fill Calculator

Evaluate insulated conductors, equipment grounding conductors, internal clamps, support fittings, device-yoke allowances, and available box volume.

Project and Box Information

Project nameLocationPrepared byDateCalculation modeCheck an actual listed box volume, or find the minimum required volume without choosing a box yet.Code-basis review settingThis does not switch to a different volume table. Any non-2023 selection marks the result Review Required and adds a verification warning.Box volume sourceUsed for reporting and review notes.Available box volume (cu in.)Use the volume marked on the box or listed by the manufacturer. Include plaster rings, extension rings, or covers only when their usable volume is listed and applicable.Notes

Insulated Conductors

Count each conductor that enters, leaves, is spliced, or terminates in the box as applicable. Do not count pigtails entirely contained within the box unless required by the selected code basis or project requirements.

Group nameOptional. Example: branch conductors, travelers, switched legs.Conductor sizeListed box-fill allowance size.QuantityWhole number.Conductor counting basisFor report notes; quantity controls the current math.

Grounds, Clamps, and Fittings

Equipment grounding conductors entering the boxUsed to determine the grounding conductor volume allowance. Verify grounding and bonding conductor counting rules against the selected code basis.Largest equipment grounding conductor sizeGrounding conductor allowance is based on the largest equipment grounding conductor entered.Internal clamps are presentSupport fitting type countCount support fitting types that require a volume allowance, such as fixture studs or hickeys. Count by fitting type, not by the number of identical fittings.

Device Yokes

Count device yokes or straps, not individual screws. A device yoke/strap volume allowance is based on the largest conductor connected to the device. Examples: receptacle, switch, dimmer, GFCI, or combination device.

Barriers, Dividers, and Other Allowances

Barrier/divider present

Barrier/divider volume impact must be verified with manufacturer data or applicable code requirements.

Result

Pass

Available box volume exceeds required volume.

Required volume

15.75 cu in.

Available box volume

24.00 cu in.

Remaining volume

8.25 cu in.

Utilization

65.6%

Verify conductor counting rules for splices, loops, pass-through conductors, and cable assemblies before use.

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Calculation Breakdown

Insulated Conductors

12 AWG insulated conductors: 6 x 2.25 cu in. = 13.50 cu in.

Grounding Conductors

Equipment grounding conductor allowance: 1.00 allowance(s) x 2.25 cu in. = 2.25 cu in.

Device Yokes

No device yoke allowance included.

Support Fittings

No support fitting allowance included.

Internal Clamps

No internal clamp allowance included.

Barriers, Dividers, and Other Allowances

No barrier, divider, or manual added allowance included.

Total

Required volume: 15.75 cu in.
Available volume: 24.00 cu in.
Remaining volume: 8.25 cu in.
Utilization: 65.6%
Box volume source: Marked box volume
Code-basis review setting: 2023 NEC

Code and Design References

NEC 314.16(B)

Box-fill calculations account for conductor, equipment-grounding conductor, clamp, support-fitting, and device-yoke volume allowances as applicable.

Verify wording, local amendments, and the adopted code edition before release.

NEC Table 314.16(B)(1)

Conductor volume allowances are selected by conductor size and expressed in cubic inches.

Keep conductor-volume data edition-controlled and independently verified.