NEC Article 314.16 Sizing Tool

NEC Box Fill Calculator

Calculate conductor volume, device yokes, internal clamps, support fittings, and equipment grounds to verify enclosure volume compliance.

Code Standard:

NEC 2020 / 2023 Standard NEC 2017 & Prior (Legacy)

Jurisdiction Advisory: NEC edition adoption and local amendments vary by state and municipality. Confirm adopted code requirements with your local Authority Having Jurisdiction (AHJ).

Sample setup loaded below (4x 12 AWG conductors, 1 device, 2 grounds in a 4" square box). Adjust any value or tap Reset.

Enclosure & Extension Ring

Determine total available cubic-inch volume per NEC 314.16(A)

Enclosure Category

Standard Metal Box Size

Typical Marked Plastic Box Volume Non-metallic boxes must use the cubic-inch capacity stamped inside the enclosure by the manufacturer (NEC 314.16(A)(2)).

Marked Enclosure Volume (cu. in.)

Add Plaster / Mud Ring or Extension Ring

Reference Ring Volume (Verify Stamped Mark)

Stamped Ring Volume (cu. in.)

Always verify the manufacturer's volume stamped directly on the installed ring per NEC 314.16(A).

Conductors Entering Box

18 AWG through 6 AWG. Pigtails that do not leave the box count as 0.

Conductors passing through without splice or termination count as 1 allowance. Each unbroken loop or coil not less than 12 inches in length counts as 2 allowances per NEC 314.16(B)(1).

Devices & Internal Fittings

Device yokes/straps, internal cable clamps, and support fittings

Device Yokes / Straps Each yoke containing 1 or more devices counts as double (2x) volume allowance. The selected wire gauge applies to all yokes entered here (NEC 314.16(B)(4)).

Largest Conductor on Device

Internal Cable Clamps Present in Box All internal clamps combined count as a single (1) volume allowance based on the largest conductor in the box (NEC 314.16(B)(2)). External connectors on the outside of the box count as 0.

Support Fittings (NEC 314.16(B)(3)) A single allowance is made for each type of support fitting present, based on the largest conductor in the box (NEC 314.16(B)(3)).

Equipment Grounding Conductors

Grounding conductors entering the enclosure (ground pigtails inside the box count as 0)

Total Ground Wires Entering Box

Largest Ground Wire Gauge

NEC Grounding Rule: First 4 grounds count as 1 allowance (2.25 cu. in.). Each ground beyond 4 adds 1/4 allowance (+0.56 cu. in.).

Recommended Enclosure Upsizing

Volume Utilization 0.0%

Total Fill Required 0.00 cu. in.

Available Box Volume 21.00 cu. in.

Remaining Capacity +21.00 cu. in.

Utilization 0.0%

Itemized Volume Breakdown (NEC 314.16)

Circuit Conductors (314.16(B)(1)) 0.00 cu. in.
Internal Cable Clamps (314.16(B)(2)) 0.00 cu. in.
Support Fittings (314.16(B)(3)) 0.00 cu. in.
Device Yokes / Straps (314.16(B)(4)) 0.00 cu. in.
Equipment Grounding (314.16(B)(5)) 0.00 cu. in.
Total Required Enclosure Volume: 0.00 cu. in.

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Methodology & Code References

Calculations on this page are based on NEC Article 314.16 and the supported NEC editions shown above. This calculator is an educational sizing aid. Verify the applicable NEC edition, product markings, and local AHJ requirements before installation.

Understanding Electrical Box Fill: The Technical Basis of NEC Article 314

Electrical box fill calculations ensure that an electrical enclosure provides adequate internal space for all installed conductors, wiring devices, cable clamps, and support fittings. Governed by Article 314 of the National Electrical Code (NEC / NFPA 70), specifically Section 314.16, box fill rules establish minimum volume allowances to prevent physical crowding inside outlet, device, and junction boxes.

When switches, receptacles, GFCIs, and dimmers are installed in an enclosure that lacks adequate cubic-inch capacity, overcrowding makes installation difficult and increases the risk of damage. Forcing conductors into an undersized box can damage wire insulation against box edges, place mechanical stress on device terminals, loosen wire splices, and restrict heat dissipation from current-carrying conductors and electronic devices. Proper box sizing ensures conductors can be installed without damage and have sufficient room for safe maintenance and operation.

NEC Code Rule

The Core Requirement of NEC Section 314.16

Boxes and conduit bodies must provide sufficient free space for all enclosed conductors. The total volume of a wiring enclosure is the combined volume of its assembled parts, including plaster rings, extension rings, and covers that are marked with their volume or made from dimensions listed in NEC Table 314.16(A). The total required volume calculated under Section 314.16(B) must never exceed the total available box volume.

NEC Box Fill Allowances and Additional Considerations

To verify whether an electrical enclosure meets code requirements, the calculation accounts for five standard volume allowances plus statutory provisions. Every component occupying space inside the enclosure receives an allowance in cubic inches ($\text{cu. in.}$) or cubic centimeters ($\text{cm}^3$) based on conductor size per NEC Table 314.16(B).

Allowance 1

Conductor Fill (NEC 314.16(B)(1))

Each conductor that originates outside the box and terminates or is spliced within the box counts as one (1) volume allowance. Each conductor that passes through the enclosure without splice or termination also counts as one (1) volume allowance.

Unbroken Loops or Coils (NEC 300.14 & 314.16(B)(1)):

Each looped or coiled conductor pulled through a box without splice or termination is counted once, except that each looped conductor not less than 300 mm (12 in.) in unbroken length must be counted as two (2) volume allowances (counted once for each 300 mm [12 in.] or fraction thereof per 314.16(B)(1)).

Pigtail Treatment (NEC 314.16(B)(1)):

Conductors that originate and terminate entirely within the box are not counted as additional conductor volume under NEC 314.16(B)(1). For example, short pigtails running from a wire connector to a receptacle terminal screw, switch terminal, or box grounding screw do not add to the calculation because the incoming conductors feeding the splice are already accounted for.

Allowance 2

Internal Cable Clamp Fill (NEC 314.16(B)(2))

Where one or more internal cable clamps (factory metal clamps located inside the enclosure) are present, a single (1) volume allowance is made based on the largest conductor present in the box.

Important Code Distinction:

Whether the box contains one, two, or four internal cable clamps, the deduction is always exactly one volume allowance. External cable connectors mounted through knockouts on the exterior of the box count as zero (0) allowances.

Mixed Gauge Rule in Action:

If a box contains both 14 AWG ($2.00\text{ cu. in.}$) and 12 AWG ($2.25\text{ cu. in.}$) conductors, the clamp deduction is $2.25\text{ cu. in.}$ (based on the largest conductor), even if the clamp physically clamps only the 14 AWG cable.

Space-Saving Field Tip:

Using external Romex connectors or EMT conduit fittings through knockouts consumes 0 allowances, saving $2.00\text{–}2.50\text{ cu. in.}$ of critical box volume compared to internal factory clamps.

Allowance 3

Support Fittings Fill (NEC 314.16(B)(3))

Where one or more luminaire studs or hickeys are present in the box, a single (1) volume allowance is made for each type of fitting present, based on the largest conductor present in the box.

If a box contains one luminaire stud (or two luminaire studs), that represents one type of fitting and counts as one allowance. If a box contains both a luminaire stud and a hickey, that represents two types of fittings and counts as two allowances.

Allowance 4

Device or Equipment Yoke Fill (NEC 314.16(B)(4))

For each yoke or strap containing one or more devices or equipment, a double (2x) volume allowance is made based on the largest conductor connected to device(s) supported by that yoke.

Device Mounting Dimensions:

Equipment or devices wider than a single 2-inch device box as described in Table 314.16(A) require double volume allowances for each gang required for mounting. For standard installations where two separate devices are mounted on two separate yokes in a 2-gang box, each yoke is counted individually (2 allowances per yoke, for 4 total allowances).

Allowance 5

Equipment Grounding Conductor Fill (NEC 314.16(B)(5))

All equipment grounding conductors entering an enclosure are pooled together. The volume deduction depends on the adopted code standard:

NEC 2020 / 2023 Standard:

Up to four (1 to 4) equipment grounding conductors count as one (1) single volume allowance based on the largest ground wire. Each additional ground wire beyond four adds one-quarter (0.25) volume allowance of that largest ground wire.

NEC 2017 & Prior (Legacy Rule):

All equipment grounding conductors combined count as one (1) single volume allowance based on the largest ground wire, regardless of whether there are two or ten ground wires.

Special Provisions

Terminal Blocks & Isolated Grounds

Two specialized enclosure volume considerations for commercial, industrial, and updated NEC installations:

Terminal Block Assemblies (NEC 2023 314.16(B)(6)):

Under the 2023 NEC, where listed terminal block assemblies are installed, add one (1) volume allowance for each block based on the largest conductor terminated to it. (Note: Standard wire nuts and push-in connectors are splicing devices and count as 0 allowances).

Isolated Equipment Grounds (NEC 250.146(D)):

Where an isolated equipment grounding conductor (IG) is installed for sensitive electronic equipment, it is pooled with all equipment grounds entering the enclosure under NEC 314.16(B)(5).

Conductor Volume Allowances: NEC Table 314.16(B)

The core mathematical reference for electrical box sizing is NEC Table 314.16(B). This table establishes the required volume allowance in cubic inches and cubic centimeters for conductor sizes 18 AWG through 6 AWG.

Conductor Size (AWG)	Free Space Required per Conductor	Metric Equivalent Volume	Example Application
18 AWG	1.50 cu. in.	24.6 cm³	Thermostats, HVAC controls, signalling circuits
16 AWG	1.75 cu. in.	28.7 cm³	Luminaire fixture wires, chime circuits
14 AWG	2.00 cu. in.	32.8 cm³	15-Amp residential lighting and branch circuits
12 AWG	2.25 cu. in.	36.9 cm³	20-Amp commercial outlets, kitchen small appliance circuits
10 AWG	2.50 cu. in.	41.0 cm³	30-Amp water heaters, electric dryers, AC compressors
8 AWG	3.00 cu. in.	49.2 cm³	40-Amp electric ranges, subpanel feeders
6 AWG	5.00 cu. in.	82.0 cm³	50-Amp/60-Amp EV chargers, subfeeders

Scope Boundary

Conductors 4 AWG and Larger: NEC Section 314.28

This calculator evaluates Table 314.16(B) conductor volume allowances for sizes 18 AWG through 6 AWG. Boxes and conduit bodies containing 4 AWG or larger conductors must also comply with NEC 314.28. This calculator does not evaluate the additional dimensional requirements of NEC 314.28.

Standard Metal Box Capacities: NEC Table 314.16(A)

For standard metal boxes, NEC Table 314.16(A) defines standard trade dimensions and minimum internal volumes. When using standard metallic boxes, electricians can reference these code-established volume ratings directly.

Box Trade Size (Inches)	Box Type / Description	Minimum Volume	Max 14 AWG (No Devices)	Max 12 AWG (No Devices)	Max 10 AWG (No Devices)
4 × 1-1/4 Square	Shallow 4-Inch Square Metal Box	18.0 cu. in.	9	8	7
4 × 1-1/2 Square	Standard 4-Inch Square Metal Box (Most Common)	21.0 cu. in.	10	9	8
4 × 2-1/8 Square	Deep 4-Inch Square Metal Box	30.3 cu. in.	15	13	12
4-11/16 × 1-1/2 Square	Standard 4-11/16" Square Box (Commercial)	29.5 cu. in.	14	13	11
4-11/16 × 2-1/8 Square	Deep 4-11/16" Square Box (High Density)	42.0 cu. in.	21	18	16
3 × 2 × 2 Device	Shallow Single-Gang Switch Box	10.0 cu. in.	5	4	4
3 × 2 × 2-1/2 Device	Standard Single-Gang Switch Box	12.5 cu. in.	6	5	5
3 × 2 × 3-1/2 Device	Deep Single-Gang Switch Box	18.0 cu. in.	9	8	7
4 × 2-1/8 × 1-7/8 Handy	Exposed Work Utility / Handy Box	13.0 cu. in.	6	5	5
4 × 1-1/2 Octagonal	Ceiling Luminaire / Junction Box	15.5 cu. in.	7	6	6
4 × 2-1/8 Octagonal	Deep Ceiling Luminaire Box	21.5 cu. in.	10	9	8

Plaster Rings, Mud Rings & Box Extensions (NEC 314.16(A))

Under NEC Section 314.16(A), the total available capacity of an electrical enclosure includes the base box volume plus the marked volume of any attached plaster rings, mud rings, extension rings, and industrial equipment covers.

Total Available Enclosure Capacity Formula

Total Available Volume = Base Box Volume + Marked Mud Ring Volume + Marked Extension Ring Volume

Under NEC 314.16(A), rings and extensions must be durably marked with their volume in cubic inches by the manufacturer to be credited toward total box volume. Always use the manufacturer's marked volume for the specific ring, extension, or cover installed. Below are typical reference catalog values for standard listed mud rings:

Plaster / Mud Ring Type	Raised Depth (Inches)	Typical Catalog Reference Volume	Common Drywall Application
Single-Gang Raised Ring	1/4" Raised	~2.0 cu. in.	Wood paneling, thin drywall
Single-Gang Raised Ring	1/2" Raised	~3.5 cu. in.	Standard 1/2" residential gypsum board
Single-Gang Raised Ring	5/8" Raised	~4.3 cu. in.	5/8" Type X commercial fire-rated drywall
Single-Gang Raised Ring	3/4" Raised	~5.5 cu. in.	Tile backer board, double drywall
Two-Gang Raised Ring	1/2" Raised	~6.0 cu. in.	Standard 2-gang switch or duplex setup
Two-Gang Raised Ring	5/8" Raised	~7.3 cu. in.	5/8" Type X fire-rated assemblies
4" Square Extension Ring	1-1/2" Deep	~21.0 cu. in.	Surface conduit drops, commercial additions

4 Practical Field Worked Examples (Step-by-Step Verification)

The following four examples show how NEC 314.16 rules apply across common residential and commercial branch-circuit installations:

Example 1

Residential Kitchen Receptacle (Mixed Wire Sizes)

Installation Details: A standard 4" × 4" × 1-1/2" metal box (21.0 cu. in.) fitted with a 1/2" raised single-gang mud ring marked 3.5 cu. in. Total available volume: 24.50 cu. in. The box contains:

Two 12/2 NM-B cables entering the box (four 12 AWG conductors spliced to device).
One 14/2 NM-B cable entering the box to power under-cabinet lights (two 14 AWG conductors spliced).
Internal cable clamps securing the NM-B cables.
One 20A duplex receptacle connected to 12 AWG wire.
Three equipment grounding conductors (two 12 AWG, one 14 AWG).

12 AWG Conductors (4 × 2.25): 9.00 cu. in.

14 AWG Conductors (2 × 2.00): 4.00 cu. in.

Internal Clamps (1 × largest wire = 12 AWG): 2.25 cu. in.

Device Yoke (2 × largest wire on device = 12 AWG): 4.50 cu. in.

Grounding (3 grounds ≤ 4, largest = 12 AWG): 2.25 cu. in.

Total Required Volume: 22.00 cu. in.

Example 2

Commercial High-Ground Feeder Box (>4 Equipment Grounds)

Installation Details: A 4" × 4" × 1-1/2" metal box without mud ring (21.0 cu. in.). Used in a commercial branch feed:

Six 12 AWG insulated circuit conductors (3 hots, 3 neutrals).
One duplex receptacle connected to 12 AWG wire.
Internal cable clamps present.
Six 12 AWG equipment grounding conductors entering from conduits.

12 AWG Conductors (6 × 2.25): 13.50 cu. in.

Internal Clamps (1 × 2.25): 2.25 cu. in.

Device Yoke (2 × 2.25): 4.50 cu. in.

Grounds (NEC 2020/2023: 1st 4 = 2.25, 2 extra @ 0.25x = 1.125): 3.375 cu. in.

Total Required Volume: 23.625 cu. in.

Example 3

Pass-Through Junction Box with 12-Inch Service Loop

Installation Details: A 4" × 4" × 1-1/2" square metal junction box (21.0 cu. in.) with blank flat cover:

Four 12 AWG conductors spliced with twist-on connectors.
One 12 AWG unbroken conductor loop of 14 inches left for future feed.
One 12 AWG equipment grounding conductor passing through.
No internal clamps, no devices, no support fittings.

Spliced 12 AWG Wires (4 × 2.25): 9.00 cu. in.

Unbroken Loop ≥12" (2 allowances × 2.25 per 314.16(B)(1)): 4.50 cu. in.

Equipment Ground (1 × 2.25): 2.25 cu. in.

Total Required Volume: 15.75 cu. in.

Example 4

Commercial 2-Gang Switch & Dimmer Box

Installation Details: A 4" × 4" × 2-1/8" deep square box (30.3 cu. in.) fitted with a 1/2" raised 2-gang mud ring marked 6.0 cu. in. Total available volume: 36.30 cu. in. Contains:

Six 14 AWG conductors (switch legs and feeds spliced).
Two 12 AWG conductors passing through without splice or termination.
Two separate devices installed (one 14 AWG 3-way switch, one 14 AWG dimmer).
Four 14 AWG equipment grounding conductors.
External EMT conduit connectors (no internal clamps).

14 AWG Conductors (6 × 2.00): 12.00 cu. in.

12 AWG Conductors (2 × 2.25): 4.50 cu. in.

Two Device Yokes (2 straps × 2 allowances × 2.00): 8.00 cu. in.

Grounding (4 grounds ≤ 4 = 1 allowance of 14 AWG): 2.00 cu. in.

Total Required Volume: 26.50 cu. in.

Box Fill vs. Conduit Fill: 5 Fundamental Differences

Apprentice electricians and estimators sometimes confuse box fill with conduit fill. While both limit conductor crowding, they are governed by separate sections of the National Electrical Code and serve different safety functions.

Engineering Parameter	Box Fill Calculations	Conduit Fill Calculations
Governing NEC Article	NEC Article 314 (Section 314.16 & Table 314.16(A)/(B))	NEC Chapter 9 (Tables 1, 4, 5, & Annex C)
Unit of Measurement	Cubic Inches ($\text{cu. in.}$) or Cubic Centimeters ($\text{cm}^3$)	Square Inches ($\text{sq. in.}$) or Square Millimeters ($\text{mm}^2$)
Primary Safety Purpose	Prevent physical crowding and damage to conductors and devices inside enclosures	Prevent excessive pulling tension and sidewall bearing pressure during wire pulls
Evaluation Basis	Calculated required cubic-inch volume must not exceed listed or marked available box volume	Total conductor cross-sectional area cannot exceed 40% of conduit interior area (for 3+ wires)
Ground Wire Treatment	1 allowance for first 4 grounds; +1/4 each beyond 4 (NEC 2020/2023)	Total cross-sectional area of bare/insulated wire counts against 40% raceway fill

For complete details on raceway pipe sizing, check out our companion tools: use our Interactive Conduit Fill Calculator for sizing EMT, PVC, and RMC, read our comprehensive guide on Conduit Fill vs. Box Fill Differences, and explore our reference on How Bare Ground Wires Count in Conduit Fill.

8 Common Box Fill Mistakes (And How to Avoid Them)

Below are eight practical box fill mistakes commonly encountered during branch-circuit rough-in and trim-out:

Mistake 1

Counting Internal Cable Clamps Individually

The Error: Deducting multiple allowances because a metal box contains two or more internal cable clamp screws.

The Code Rule: NEC 314.16(B)(2) states that one or more internal cable clamps count as one single volume allowance based on the largest conductor present, regardless of how many internal clamps exist.

Mistake 2

Omitting Equipment Grounding Conductors

The Error: Leaving bare or green grounding conductors out of the calculation entirely.

The Code Rule: Grounds occupy physical space. Under Section 314.16(B)(5), grounds must be included: 1 allowance for up to four grounds, plus 0.25 allowance for each ground beyond four.

Mistake 3

Installing Bulky Devices in Shallow Enclosures

The Error: Placing a deep GFCI, smart dimmer, or USB outlet into a shallow 10.0 or 12.5 cu. in. device box.

The Practical Fix: While the NEC specifies 2 volume allowances for standard device yokes, physically bulky devices leave very little room for wire folding. Use 18.0 cu. in. deep boxes or 4" square boxes with plaster rings for electronic devices.

Mistake 4

Counting Pigtails as Additional Conductor Fill

The Error: Adding extra volume allowances for short pigtail jumpers connecting a splice to an outlet screw.

The Code Rule: Conductors that originate and terminate entirely within the box count as zero (0) allowances per NEC 314.16(B)(1). Counting them results in unnecessarily oversized boxes.

Mistake 5

Overlooking Unbroken 12-Inch Conductor Loops

The Error: Counting a 14-inch loop of wire left in a junction box as a single conductor.

The Code Rule: Under NEC 314.16(B)(1) and 300.14, any unbroken conductor loop of 12 inches or longer must be counted as two (2) volume allowances.

Mistake 6

Applying Raceway Area Rules (Chapter 9) to Boxes

The Error: Trying to calculate box fill using conductor square inches from Chapter 9 Table 5 instead of cubic inches from Table 314.16(B).

The Code Rule: Cross-sectional area in square inches applies to raceways (conduit). Enclosures are always sized in cubic inches per Article 314.

Mistake 7

Forgetting to Credit Plaster Ring Volume

The Error: Sizing a 4" square box based solely on its 21.0 cu. in. base volume, forgetting that the 1/2" raised mud ring adds 3.5 to 6.0 cu. in.

The Practical Fix: Check the stamped volume on the mud ring and add its cubic inches to the box capacity under NEC 314.16(A).

Mistake 8

Using Box Fill on Conductors 4 AWG and Larger

The Error: Attempting to calculate cubic-inch volume allowances for 4 AWG, 2 AWG, or 1/0 AWG conductors in a pull box.

The Code Rule: Table 314.16(B) stops at 6 AWG. Boxes containing 4 AWG and larger conductors must also comply with the raceway spacing rules of NEC Section 314.28.

Frequently Asked Questions (NEC Box Fill)

How many 12 AWG wires can fit in a standard 4-inch square box?

Under NEC Table 314.16(A), a standard 4" × 4" × 1-1/2" metal square box (21.0 cu. in.) has a listed maximum capacity of nine (9) 12 AWG conductors. This maximum applies only under the baseline condition of a splice or junction box where no devices, internal cable clamps, support fittings, or equipment grounding conductors are installed (21.0 / 2.25 = 9.33, rounded down to 9). When internal clamps, grounds, or device yokes are added, allowable wire count decreases accordingly.

Do twist-on wire connectors or crimp sleeves count toward box fill?

No. Standard twist-on wire connectors, push-in connectors, and crimp sleeves do not receive an individual volume deduction under NEC Article 314.16. Where listed terminal block assemblies are installed under NEC 2023 Section 314.16(B)(6), they must be calculated separately.

Are pigtails counted in box fill calculations?

No, pigtails that remain inside the box count as zero (0) allowances. Conductors that originate and terminate entirely within the box are not counted as additional conductor volume under NEC 314.16(B)(1). A short wire connecting a splice to an outlet screw terminal consumes no additional box fill allowance.

How do equipment ground wires count under NEC 2020 and 2023?

Under Section 314.16(B)(5), up to four equipment grounding conductors entering an enclosure count as one (1) single volume allowance based on the largest ground wire present. Each additional ground wire beyond four adds an extra one-quarter (0.25) volume allowance based on that same largest ground wire.

How much volume does a standard duplex receptacle or light switch take?

Under NEC Section 314.16(B)(4), each mounting yoke or strap containing one or more devices counts as a double (2x) volume allowance based on the largest conductor connected to that device (4.00 cu. in. for 14 AWG; 4.50 cu. in. for 12 AWG).

Do external cable connectors (outside the box) count toward box fill?

No. External cable connectors (such as standard squeeze connectors or snap-in Romex connectors mounted through knockouts from the exterior) do not occupy internal enclosure space and count as zero (0) allowances. Only internal clamps located inside the box count under NEC 314.16(B)(2).

What size box is needed for four 12/2 Romex cables and a receptacle?

Four 12/2 cables bring eight 12 AWG circuit wires (8 × 2.25 = 18.0 cu. in.), four 12 AWG grounds (1 allowance = 2.25 cu. in.), one receptacle yoke (2 allowances = 4.5 cu. in.), and internal clamps (1 allowance = 2.25 cu. in.). Total required volume = 27.0 cubic inches. A standard 21.0 cu. in. box is insufficient. You must use a 4" × 4" × 2-1/8" deep box (30.3 cu. in.) or a 4" square box with a raised mud ring.

How do plastic (non-metallic) boxes differ from metal boxes in box fill?

Metal boxes are governed by standard minimum volume dimensions listed in NEC Table 314.16(A). Non-metallic (plastic or fiberglass) boxes vary by manufacturer design. Under NEC 314.16(A)(2), non-metallic boxes must have their cubic-inch volume durably marked on the interior by the manufacturer, and that marked capacity must be used for box fill evaluations.

Complete Electrical Raceway & Sizing Resource Hub

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