Conduit 1Left side
Pull Box Size Calculator
Pull Box Size Calculator
Add each physical conduit by its enclosure-entry surface and trade size, including back entries opposite the cover. New here? Read the quick guide.
Pull Box Size Calculation
Project and proposed enclosure
- Project
- Not provided
- Location
- Not provided
- Prepared by
- Not provided
- Display units
- Imperial — inches
- Application
- Power conductors — NEC 314.28
- Proposed inside box
- 8 in × 8 in × 4 in
Physical conduits
| Conduit | Entry | Size | Back-entry conductor (optional) |
|---|---|---|---|
| 1 | Left side | 1″ | — |
| 2 | Right side | 1″ | — |
Conduit connections
| Connection | Rule | From | To |
|---|---|---|---|
| 1 | Straight | Conduit 1 | Conduit 2 |
Project details (optional)Add details
Calculation setup
Choose the cable application
Conduit trade sizes and power-conductor clearances govern the calculation.
Physical enclosure-entry layout
Conduits and conductor connections
Add each physical conduit once. One conduit can connect to one or several other conduits.
Start with the conduits. The connection list is created automatically and can be changed for an unusual layout.
Part 1
Conduits
Conduit 2Right side
Advanced routing (optional)Only open this when the conductors do not run from Conduit 1 to each added conduit.
Conduit connections
The calculator creates these connections automatically. Change them only for unusual routing, or to identify a splice or tap in the box.
Connection 1Straight pull
Opposite plan-view sides use the straight-pull rule.
Complete enclosure check
Proposed inside box dimensions
Start with a standard enclosure plan below or enter custom usable inside dimensions. Calculated minima come from the entered power-conductor pull layout; ungoverned dimensions still require project verification.
No conduit enters through the Back, so depth remains a separately verified project input. Verify conductor bending space, splices, hubs, cover orientation, and the selected enclosure.
Reports and sharing
Save or share this calculation
Exports are created locally when requested and do not delay the calculator's initial page load.
Layout preview
Pull box and connected conduits
Selected standard enclosure · proportional 8 in × 8 in plan view
Pull boxL 8 inW 8 in
Selected standard enclosure8 in × 8 inL ≥ 8 inW ≥ 1.31 inD 4 in proposedD minimum 1.31 in
C21″ conduitRight side
C11″ conduitLeft side
Calculated result
Minimum enclosure planning dimensions
Sets each inside dimension to its numeric screening floor. This is not a standard-box selection or a fitting-layout approval.
Inside length≥ 8 inConnection 1: straight pull between left and right box sidesProposed length passes
Inside width≥ 1.31 in1 bare raceway opening across the left box side. Bare-raceway screen only; verify fittings and usable wall area.Proposed width passes
Inside depth≥ 1.31 inLargest bare raceway outside diameter entering a box side. A fitting or hub normally needs more wall area.Proposed depth passes
This is the smallest nominal planning size in the calculator's common reference list that clears the bare-raceway opening screen and the other numeric dimensions calculated by this workflow.
Reference dimensions are nominal and may differ from usable inside dimensions. The opening screen uses bare-raceway outside diameters; verify connector or hub dimensions, knockout placement, usable wall area, and a specific enclosure before specification.All dimension checks
Connection 1: straight pull between left and right box sideslength: 8 × 1 = 8 in
Physical raceway-opening screen
1 bare raceway opening across the left box sidewidth: 1.315 = 1.31 in
1 bare raceway opening across the right box sidewidth: 1.315 = 1.31 in
Largest bare raceway outside diameter entering a box sidedepth: max(1.315, 1.315) = 1.31 in
Bare-raceway outside diameters establish only a geometric floor. Verify the actual connector or hub, locknut, knockout spacing, edge clearance, and usable enclosure wall area.
The proposed box is 8 in × 8 in × 4 in inside. Calculated minima come from the entered power-conductor pull layout. Back entries can govern depth through the cover-clearance exception; otherwise 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
A continuous conductor path between opposite plan-view sides creates a straight pull. Different non-opposite entry surfaces create an angle pull, and two conduits entering through the same surface create a U pull. Select splice or tap whenever conductors are joined in the box; that rule applies even when the connected conduits are on opposite plan-view sides.
Straight pulls use eight times the largest connected conduit. For angle pulls, U pulls, and splices or taps, all conduits on each affected plan-view side are grouped conservatively using six times the largest conduit plus the other conduit trade sizes. The largest applicable requirement governs length or width. For a Back entry opposite the cover, optional largest-conductor data enables the NEC 314.28(A)(2) and Table 312.6(A) one-wire-per-terminal depth check. Omitted entries receive no assumed conductor size and remain clearly marked for project verification.
Connected-entry spacing is reported as a required minimum, not a verified layout result. Confirm actual knockout-center spacing on the selected enclosure.
Scope and verification
This calculation is intended for conduits containing insulated conductors 4 AWG and larger. Back-entry depth uses the conservative all-other-conductors column; compact AA-8000 aluminum requires separate verification. Verify conductor bending space, splices, taps, shields, 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 pulls, U pulls, and splices sized?
All conduits entering through each affected box side are grouped conservatively using six times the largest conduit trade size plus the trade sizes of the other conduits on that side. Select splice or tap when conductors are joined in the box, even if the connected conduits enter through opposite sides.
What does entry surface mean?
Entry surface means where the conduit penetrates the enclosure. Left, right, top, and bottom are the four plan-view sides. Back means the mounting surface opposite the cover; it does not mean a second building wall.
Do conduits entering through the back affect pull-box depth?
They can. The largest power conductor is optional for each Back entry. When every Back entry includes it, the calculator uses NEC 314.28(A)(2) and the Table 312.6(A) one-wire-per-terminal value to check minimum front-to-cover depth. If the data is omitted, the plan remains usable but shows REVIEW and leaves depth unverified; partial data produces only a provisional depth. No conductor size is assumed.
Can the calculator handle multiple conduits?
Yes. Add each physical conduit, choose the side of the box it enters and its trade size, and the calculator automatically connects new conduits to Conduit 1. One conduit can connect to several outgoing conduits, and the connection can be changed when the actual routing is different.
Can I plan a pull box for communications or low-voltage cable?
Yes. Choose Communications / low-voltage cable for a quick-planning REVIEW using the proposed enclosure and conduit layout. When manufacturer data is available, optionally add the governing cable or bundle outside diameter, installation and installed bend radii, routing clearance, and bend plane for a conservative bend-radius check.
Can I plan a pull box for fiber-optic cable?
Yes. Fiber mode supports quick planning without cable details. Optionally add the actual cable's installation and long-term bend radii and outside diameter to calculate a conservative full-bend envelope. Verify manufacturer instructions, maximum pulling tension, splice trays, service loops, entry locations, and project requirements before selecting an enclosure.
Can I download or share a pull-box calculation?
Yes. You can print a branded report, save it as PDF, download a branded SVG or PNG diagram, download the calculation as CSV, or copy a link that restores the entered conduit layout and proposed box dimensions.