Pull Box and Junction Box Sizing Calculator
Estimate minimum interior dimensions for straight, angle, U, and splice pulls involving 4 AWG and larger conductors.
Pull arrangement
Article 314.28 sizing is for pulls involving conductors 4 AWG and larger.
Raceway row 1
Use the same run letter for raceway entries enclosing the same conductors.
Use the same run letter for raceway entries enclosing the same conductors.
Raceway row 2
Use the same run letter for raceway entries enclosing the same conductors.
Minimum pull-box dimensions
| Raceway row | Dimension | Largest raceway | Other raceways in row | Minimum |
|---|---|---|---|---|
| 1 | length | 2 in | 1 in | 13 in |
| 2 | width | 1.25 in | 0 in | 7.5 in |
About this calculator
Estimate minimum interior box dimensions for straight, angle, U, and splice pulls involving conductors 4 AWG and larger. Enter the raceway trade sizes and how each row enters the box.
The largest conductor size determines whether Article 314.28 applies. Raceway trade sizes determine the required dimensions. This is a geometric pull-box screen, not a box-fill calculation.
Method and assumptions
For straight pulls, the minimum interior length is 8 times the trade size of the largest raceway entering the box.
For each angle, U, or splice-pull row, the required distance from the raceway entry wall to the opposite wall is 6 times the largest raceway trade size in the row, plus the sum of the trade sizes of the other raceways in that row. The calculator takes the largest requirement for each selected box dimension.
When entries marked with the same conductor path contain the same conductors, the calculator reports a separate minimum spacing of 6 times the larger raceway trade size. Confirm the actual layout and measurement reference in the adopted code.
Example
An angle pull with a 2 in. and a 1 in. raceway in one row requires 6 × 2 + 1 = 13 in. from that entry wall to the opposite wall. A single 1-1/4 in. raceway in a second row on the other box axis requires 6 × 1-1/4 = 7.5 in. A conductor path shared by 2 in. and 1 in. entries requires 12 in. minimum entry spacing.
These calculations do not determine the box’s complete physical size or verify conductor bend radius, equipment access, or installation suitability.
Interpret the result
Use the reported length and width as minimum interior dimensions for the entered pull arrangement. If the calculator reports only one dimension, the entered rows did not establish the other dimension.
Raceway rows, entry locations, and conductors must match the actual box. Confirm the full raceway arrangement, same-conductor paths, conductor bending space, enclosure listing, and locally adopted code before installation.
FAQs
Why does the calculator ask for conductor size?
The selected largest conductor determines whether the Article 314.28 pull-box sizing formulas apply. The dimensions themselves use raceway trade sizes, not conductor AWG or kcmil size.
How are raceway rows used?
For angle, U, and splice pulls, enter each row of raceway entries on a wall. Select whether the dimension measured from that wall to the opposite wall is the box length or width. The calculator reports the largest row requirement for each dimension.
Why do I assign the same-conductor path?
Raceway entries marked with the same path carry the same conductors through the box. The calculator reports the minimum separation for those entries separately from the box dimensions.
Does this calculate box fill volume?
No. Pull-box dimensions under Article 314.28 are separate from box-fill volume allowances. Use the Box Fill Calculator for conductor volume in outlet and device boxes.
Does this calculate bending space for every conductor?
No. It calculates the minimum dimensions from the entered raceway arrangement. Confirm conductor bending space, box listing, access, supports, and other installation requirements for the actual pull.
Sources
- NFPA 70, National Electrical Code, 2026 edition — Section 314.28 pull and junction box dimensions. Verify the edition adopted by the authority having jurisdiction.
- NFPA 70 Chapter 9 First Draft Report, preliminary report — public code-development material for pull-box sizing provisions.
- NFPA 70 Chapter 3 Second Draft Report, preliminary report — public code-development material on conductor size scope and same-conductor raceway spacing.