Run 1Straight pull
Left wall → Right wall. The largest paired conduit governs the 8× dimension.
Pull Box Size Calculator
Pull Box Size Calculator
Place paired conduit entries on the four box walls to calculate minimum pull-box dimensions for straight, angle, and U pulls.
Four-wall layout
Conduit runs
Each run represents conductors entering through one conduit and leaving through its paired conduit.
Wall group identifies openings aligned together on the same box wall. Use the same group for one row of openings and a different group for a separate row.
Complete enclosure check
Proposed inside box dimensions
Enter the usable inside dimensions of a proposed enclosure. Length and width are checked against the conduit layout.
Depth is recorded as a project input, not calculated from the 314.28 plan-view multipliers. Verify it for conductor bending space, splices, hubs, cover orientation, and the selected enclosure.
Layout preview
Pull box and connected conduits
Pull box
Minimum inside planL ≥ 8 inW 8 in proposedD 4 in proposed
1B1″ conduitRight wall · Group 1
1A1″ conduitLeft wall · Group 1
Calculated result
Minimum enclosure dimensions
Inside length≥ 8 inConduit run 1: straight pull between left and right wallsProposed length passes
Inside width8 in proposedNo top/bottom rule is triggered by this layout; review the proposed dimension for physical fitProposed width passes
Inside depth4 in proposedVerify conductor bending space, splices, entries, and enclosure constructionProject verification required
All dimension checks
Conduit run 1: straight pull between left and right wallslength: 8 × 1 = 8 in
The proposed box is 8 in × 8 in × 4 in inside. Calculated length and width minima come from the entered pull layout; depth remains a separately verified project input. Compare usable inside dimensions—not nominal catalog dimensions.
How the calculation works
Mixed pull types in one box
Opposite walls create a straight pull. Adjacent walls create an angle pull. Two entries on the same wall create a U pull. The calculator checks all runs and reports the largest requirement governing each plan dimension.
For straight pulls, eight times the largest paired conduit governs. For angle and U pulls, each wall group is checked using six times its largest conduit plus the other conduit trade sizes in that same aligned row. Separate wall groups keep unrelated rows from being combined.
Terminology and scope
NEC 314.28 uses the broader term “raceway.” This interface says “conduit” because its current inputs are conduit trade sizes. The calculation is intended for raceways containing insulated conductors 4 AWG and larger. Verify conductor bending space, splices, taps, shields, removable covers, local amendments, and the final listed enclosure with the authority having jurisdiction.
Planning conduits first? Use the Conduit Size Calculator before laying out the pull box.
Pull-box sizing FAQ
Common pull-box calculation questions
How do you size a pull box for a straight pull?
For conductors covered by NEC 314.28(A)(1), the minimum inside dimension in the straight-pull direction is eight times the trade size of the largest conduit in that pull.
How are angle and U pull boxes sized?
For each applicable aligned row (called a wall group in this calculator), use six times the largest conduit trade size plus the trade sizes of the other conduit entries in that group. The governing wall calculation sets the corresponding inside dimension.
Why is pull-box depth entered separately?
The straight, angle, and U-pull multipliers establish plan-view clearances but do not create one universal enclosure depth. Depth must be checked for conductor bending space, splices, hubs, covers, and the usable dimensions of the selected enclosure.
Can the calculator handle multiple conduits?
Yes. Add paired conduit runs, assign each entry to a box wall and wall group, and the calculator evaluates the straight, angle, U-pull, and paired-entry spacing requirements together.