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Pull Box Size Calculator (NEC 314.28)

Enter the raceways on each wall. Get the box's minimum length and width, each step with its NEC cite.

Field brief
Straight pulllength at least 8 times the largest straight-through raceway's trade size.NEC 314.28(A)(1)
Angle or U pull, or splice6 times the largest raceway in a row, plus every other entry in that row, to the opposite wall.NEC 314.28(A)(2)
Applies toraceways with conductors of 4 AWG or larger required to be insulated, and cables with conductors of 4 AWG or larger.NEC 314.28(A)
Left wall
Row 1
Right wall

No raceway on this wall.

Top wall

No raceway on this wall.

Bottom wall
Row 1

A raceway added from a reading enters as an angle, U or splice entry; change it to straight through if its conductors pass to the opposite wall unspliced. A fill reading also sets the largest conductor when its conductors are larger.

Length, left wall to right wall14 in.
Width, top wall to bottom wall14 in.
  • Length: at least 14 in. (314.28(A)(2)).
  • Width: at least 14 in. (314.28(A)(2)).
  • Entries enclosing the same conductor, the larger raceway 2 in.: at least 12 in. apart (314.28(A)(2)).

From NFPA 70, 2023 edition, 314.28. The NEC 2020 (pages 70-187 and 70-188) and the NEC 2026 (page 70-241) print the same minimum dimensions: the eight and six times, the 4 AWG scope, the row rule and the same-conductor spacing. These are minimums; the box you install may be larger.

NEC 2020: it numbers the over-1000-volt rules Part IV.

NEC 2026: its 314.28(A)(2) Exception reads "opposite a cover" and cites Table 312.9(A); its 314.28(B) reads "secured in an approved manner"; its over-1000-volt part starts "over 1000 Volts ac, 1500 Volts dc".

What else 314.28 says

  • Applies to raceways containing conductors of 4 AWG or larger that are required to be insulated, and to cables containing conductors of 4 AWG or larger, on systems of 1000 volts or less; in a raceway, a conductor not required to be insulated does not count (314.28(A); over 1000 volts, Part III and 314.71).
  • A trade size counts as its inch figure: 1-1/4 is 1.25 in. (314.28(A)).
  • A straight-through entry's conductors leave by the opposite wall: enter that raceway on the opposite wall too (314.28(A)(1)).
  • A cable entry counts as the smallest raceway trade size the number and size of conductors in the cable require (314.28(A)(2)).
  • The depth is not sized here. Where an entry is in the wall opposite a removable cover, the distance from that wall to the cover may be the one-wire-per-terminal distance of Table 312.6(A) (314.28(A)(2), Exception).
  • A listed box or listed conduit body smaller than these is permitted for combinations of conductors less than the conduit or tubing fill Chapter 9 Table 1 permits (314.28(A)(3)).
  • A listed conduit body smaller than the angle-pull distance, with a centerline radius not less than Chapter 9 Table 2's for one-shot and full-shoe benders, is permitted for the conductor combinations Chapter 9 Table 1 permits, where it is marked as evaluated for this (314.28(A)(3)).
  • A box or conduit body listed for fewer conductors than Chapter 9 Table 1 permits is marked with their maximum number and size; for other conductors, the fill's area does not exceed the area of the conductors its marking names (314.28(A)(3)).
  • A box with any dimension over 6 ft: all conductors cabled or racked up in an approved manner (314.28(B)).
  • Covers compatible with the box and suitable for the conditions of use; a metal cover grounded as 250.110 requires (314.28(C)).
  • A box with permanent barriers: each section is a separate box (314.28(D)).
  • Power distribution blocks are permitted in boxes over 100 cubic inches, as 314.28(E)(1) through (E)(5) set out; an equipment grounding terminal bar is permitted in a smaller box (314.28(E) and its Exception).
  • A terminal housing supplied with a motor follows 430.12 instead (314.28, Exception).
  • The box is also of an approved size to provide free space for all enclosed conductors (314.16).
Show the math
  1. GIVENEdition: NEC 2023
  2. GIVENLargest conductor required to be insulated: 3/0 AWG
  3. GIVENLeft wall: row 1, 2 in. angle, U or splice, 2 in. angle, U or splice
  4. GIVENBottom wall: row 1, 2 in. angle, U or splice, 2 in. angle, U or splice
  5. MATHLeft wall to the opposite wall, row 1: 6 × 2 in. + 2 in. = 14 in.NEC 2023 314.28(A)(2)
  6. MATHBottom wall to the opposite wall, row 1: 6 × 2 in. + 2 in. = 14 in.NEC 2023 314.28(A)(2)
  7. MATHEntries enclosing the same conductor, the larger raceway trade size 2: 6 × 2 in. = 12 in. apartNEC 2023 314.28(A)(2)
  8. RESULTLength (left wall to right wall): at least 14 in.NEC 2023 314.28(A)(2)
  9. RESULTWidth (top wall to bottom wall): at least 14 in.NEC 2023 314.28(A)(2)
Where this number comes fromIntry Verified
Calculated from
NEC 2023 314.28(A)(1) and (A)(2) (NFPA 70, 2023 edition, page 70-200). The box's minimum length and width from NEC 314.28(A)(1) (eight times the largest straight-through raceway) and 314.28(A)(2) (six times the largest raceway in a row plus every other entry in that row), from the NEC 2023; the 2020 and 2026 editions print the same minimum dimensions. See the full receipt ↓
Run with
  • Edition2023
  • Largest conductor required to be insulated3/0 AWG
  • Raceways4
Checked
Every figure an Intry calculator computes comes from a locked source module, not hand-typed. 32786 automated checks, one suite for the whole site rather than a per-tool count, re-derive the numbers before each deploy from the tables this site holds, read from the cited NEC section. This is our own deterministic gate, not a third-party audit.
Final say
Your AHJ and local amendments have final say. Confirm before rough-in.
What Intry Verified means

Intry Verified · NEC 2023 · Build D331505 · 2026-10-24

Pull boxAt least 14 in. long by 14 in. wide; entries enclosing the same conductor at least 12 in. apart (6 × 2 in.)

From NFPA 70, the 2023 edition, 314.28; the 2020 and 2026 editions print the same minimum dimensions (each reading notes where their words change a rule). Your inspector has the final word.

How to use the pull box calculator

  1. Set the largest conductor. Pick the largest conductor required to be insulated (in a cable, its largest conductor). The rule applies at 4 AWG or larger.
  2. Enter each wall's raceways. For each wall, add its raceways in rows, each with its trade size and whether its conductors pull straight through unspliced or turn, U-turn or splice.
  3. Read the minimums. The tool gives the minimum length (left to right) and width (top to bottom), the spacing between entries of the same conductors, and the rest of 314.28 that applies.

Rows and walls

314.28(A)(2) figures each row of raceways on a wall alone and uses the row that needs the most room. Once any entry turns, U-turns or is spliced, the code reads the distance from each raceway entry to the opposite wall, so every row on every wall is figured, straight-through entries included. A cable entry counts as the smallest raceway its conductors would need.

Worked examples

Example 1: a straight pull, two 3 in. conduits

Pull box at least 24 in. long; width not set by a straight pull or a row (NEC 2023 314.28(A)).

Show the math
  1. GIVENEdition: NEC 2023
  2. GIVENLargest conductor required to be insulated: 4/0 AWG
  3. GIVENLeft wall: row 1, 3 in. straight through
  4. GIVENRight wall: row 1, 3 in. straight through
  5. MATHStraight pull on the left or right wall: 8 × 3 in. (trade size 3, the largest straight-through raceway) = 24 in.NEC 2023 314.28(A)(1)
  6. RESULTLength (left wall to right wall): at least 24 in.NEC 2023 314.28(A)(1)
  7. RESULTWidth (top wall to bottom wall): not set by 314.28(A)(1) or (A)(2) here: no raceway enters the top or bottom wallNEC 2023 314.28(A)

Example 2: an angle pull, two 2 in. conduits each way

Pull box at least 14 in. long by 14 in. wide; entries enclosing the same conductor at least 12 in. apart (6 × 2 in.) (NEC 2023 314.28(A)).

Show the math
  1. GIVENEdition: NEC 2023
  2. GIVENLargest conductor required to be insulated: 3/0 AWG
  3. GIVENLeft wall: row 1, 2 in. angle, U or splice, 2 in. angle, U or splice
  4. GIVENBottom wall: row 1, 2 in. angle, U or splice, 2 in. angle, U or splice
  5. MATHLeft wall to the opposite wall, row 1: 6 × 2 in. + 2 in. = 14 in.NEC 2023 314.28(A)(2)
  6. MATHBottom wall to the opposite wall, row 1: 6 × 2 in. + 2 in. = 14 in.NEC 2023 314.28(A)(2)
  7. MATHEntries enclosing the same conductor, the larger raceway trade size 2: 6 × 2 in. = 12 in. apartNEC 2023 314.28(A)(2)
  8. RESULTLength (left wall to right wall): at least 14 in.NEC 2023 314.28(A)(2)
  9. RESULTWidth (top wall to bottom wall): at least 14 in.NEC 2023 314.28(A)(2)

Example 3: three conduits turning the corner

Pull box at least 22 in. long by 22 in. wide; entries enclosing the same conductor at least 6 × the larger raceway apart (12 in. where the larger is 2 in., 18 in. where the larger is 3 in.) (NEC 2023 314.28(A)).

Show the math
  1. GIVENEdition: NEC 2023
  2. GIVENLargest conductor required to be insulated: 500 kcmil
  3. GIVENLeft wall: row 1, 3 in. angle, U or splice, 2 in. angle, U or splice, 2 in. angle, U or splice
  4. GIVENTop wall: row 1, 3 in. angle, U or splice, 2 in. angle, U or splice, 2 in. angle, U or splice
  5. MATHLeft wall to the opposite wall, row 1: 6 × 3 in. + 2 in. + 2 in. = 22 in.NEC 2023 314.28(A)(2)
  6. MATHTop wall to the opposite wall, row 1: 6 × 3 in. + 2 in. + 2 in. = 22 in.NEC 2023 314.28(A)(2)
  7. MATHEntries enclosing the same conductor, the larger raceway trade size 2: 6 × 2 in. = 12 in. apartNEC 2023 314.28(A)(2)
  8. MATHEntries enclosing the same conductor, the larger raceway trade size 3: 6 × 3 in. = 18 in. apartNEC 2023 314.28(A)(2)
  9. RESULTLength (left wall to right wall): at least 22 in.NEC 2023 314.28(A)(2)
  10. RESULTWidth (top wall to bottom wall): at least 22 in.NEC 2023 314.28(A)(2)

Frequently Asked Questions

How do you size a pull box for a straight pull?

NEC 314.28(A)(1): in a straight pull, the length of the box is at least 8 times the trade size of the largest raceway. Two 3 in. conduits pulling straight through need a box at least 24 in. long. The rule applies where the conductors are 4 AWG or larger.

How do you size a pull box for an angle or U pull?

NEC 314.28(A)(2): the distance from each raceway entry to the opposite wall is at least 6 times the trade size of the largest raceway in its row, plus the trade sizes of every other raceway entry in that row on the same wall. Each row is figured alone and the largest row is used. The same rule applies where conductors are spliced in the box. A 3 in., a 2 in. and a 2 in. conduit in one row need 6 × 3 + 2 + 2 = 22 in. to the opposite wall.

How far apart do the two raceways of the same conductors have to be?

NEC 314.28(A)(2): raceway entries enclosing the same conductor are at least 6 times the trade size of the larger raceway apart. A conductor entering in a 3 in. conduit and leaving in a 2 in. one needs 6 × 3 = 18 in. between the two entries.

Do the 314.28(A) minimum dimensions apply to 6 AWG or smaller wire?

No. 314.28(A) sets these minimum dimensions for raceways containing conductors of 4 AWG or larger that are required to be insulated (a bare conductor does not count), and for cables containing conductors of 4 AWG or larger. With smaller conductors this tool states no size. The rest of 314.28 still applies to the box, a metal cover grounded under 314.28(C) among it, and 314.16 sets its volume: the box fill calculator gives a box's cubic inches.

What if the box is more than 6 ft on a side?

NEC 314.28(B): in a pull or junction box with any dimension over 1.8 m (6 ft), all conductors are cabled or racked up in an approved manner (the 2026 edition says secured in an approved manner). The tool flags a minimum over 72 in.

How deep does the box have to be?

This tool does not size the depth. Where a raceway or cable enters the wall opposite a removable cover, the 314.28(A)(2) Exception lets the distance from that wall to the cover be the distance Table 312.6(A) requires for one wire per terminal (in the 2026 edition: opposite a cover, Table 312.9(A)).

Can I use a smaller listed box or conduit body?

314.28(A)(3) permits a listed box or listed conduit body smaller than these dimensions for combinations of conductors less than the conduit or tubing fill Chapter 9 Table 1 permits, where it is marked for them. Read its marking; this tool gives the dimensions the general rule sets.

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