Pull Box Sizing Calculator

Calculator Inputs

Project or panel name

Measurement unit

Pull type

Largest horizontal straight raceway

Largest vertical straight raceway

Largest paired U-pull raceway

Width controlling same-row raceways

Use the row on left or right walls that controls width.

Height controlling same-row raceways

Use the row on top or bottom walls that controls height.

Design margin percent

Round up increment

Existing or planned width

Existing or planned height

Optional box depth

Show area and volume values

Formula Used

Straight pull: minimum dimension equals 8 × largest raceway trade size on that pull axis.

Angle, U, or splice pull: minimum wall-to-opposite-wall distance equals 6 × largest raceway in the same row + the sum of the remaining raceways in that row.

Combination pull: calculate every applicable rule. Use the largest controlling width and height.

U-pull spacing: raceways enclosing the same conductors should be checked with 6 × the largest paired raceway.

Final recommendation: base requirement × (1 + margin percent) rounded up to your selected increment.

How to Use This Calculator

Select inches or millimeters.
Choose the pull type used in the box.
Enter the largest raceway for each straight pull axis.
Enter same-row raceway sizes for angle, U, or splice checks.
Add a design margin and rounding increment.
Enter existing box dimensions when you want a pass or review note.
Press the calculate button and review the result below the header.
Download the CSV or PDF report for records.

Example Data Table

Case	Input	Formula	Minimum Result
Straight feeder	4 in largest raceway	8 × 4	32 in
Angle row	3 in and 2 in raceways	6 × 3 + 2	20 in
U-pull spacing	2.5 in paired raceway	6 × 2.5	15 in
Combination width	Straight 24 in, angle 26 in	Use larger value	26 in before margin

Pull Box Sizing Guide

Pull box sizing protects conductors during installation. It also helps crews plan raceway layouts before a box is ordered. A pull box may handle straight pulls, angle pulls, U pulls, or splices. Each case needs a different check. This page keeps those checks in one place.

Why sizing matters

A straight pull is the simplest case. Conductors enter one wall and leave through the opposite wall. The minimum dimension in that pull direction is eight times the largest raceway trade size. When straight pulls run in two directions, check each axis separately. The width may be controlled by left and right raceways. The height may be controlled by top and bottom raceways.

Angle and U pull checks

Angle pulls and U pulls need more care. For a checked wall, find the row of raceways that creates the largest need. Multiply the largest raceway in that row by six. Then add the remaining raceway sizes in the same row. That value is the minimum distance from that wall to the opposite wall. For U pulls, also check spacing between the raceways that contain the same conductors.

Combination boxes

Combination boxes should use the largest controlling result. A box with both straight and angle pulls must satisfy both rules. The calculator compares width and height results. It then adds your chosen design margin. You can also enter an existing box size. The report shows whether the planned box appears large enough.

Field data tips

Use clean field data. Enter raceway trade sizes in the same unit. Keep each angle row separate. Do not combine raceways from different rows unless they actually share the same row. Use the largest row on each checked wall. Add a margin when future circuits may be installed. Round up to the next practical increment when ordering.

Final review

This tool is a planning aid. It does not replace code review, engineered drawings, or local inspection. Raceway arrangement, conductor size, covers, barriers, bends, and manufacturer limits can affect final approval. Always verify the layout with the authority having jurisdiction. Save the CSV or PDF report for estimating, review notes, and field discussion.

Good documentation also matters. A saved report gives estimators a simple record. It lists assumptions, units, margin, and controlling rules. That record helps compare bids, drawings, and field changes quickly later.

Frequently Asked Questions

What is a pull box sizing calculator?

It estimates minimum pull box dimensions from raceway sizes and pull type. It helps compare straight, angle, U, splice, and combination checks before final field review.

Which unit should I use?

Use one unit for every input. Do not mix inches and millimeters in the same calculation. The result will use the unit you selected.

How is a straight pull calculated?

For a straight pull, enter the largest raceway on the pull axis. The calculator multiplies that size by eight for the minimum dimension.

How is an angle pull calculated?

Enter the raceways in the same controlling row. The calculator multiplies the largest by six, then adds the remaining raceways in that row.

Does this calculator handle U pulls?

Yes. It uses the angle style row rule for box size. It also reports a separate spacing check for the paired U-pull raceways.

What does combination pull mean?

A combination pull has more than one pull condition. The calculator checks straight and row-based requirements, then uses the larger controlling dimension.

Why add a design margin?

A margin allows space for field tolerance, layout changes, and future raceways. It is added before rounding to the selected ordering increment.

Can this replace an inspection?

No. It is a planning tool. Always confirm final dimensions with project drawings, local rules, product instructions, and the authority having jurisdiction.