What is a box offset?

A box offset is a small double bend right at the end of a conduit that steps it up so the connector seats square into a box knockout. The box stands off the surface by its own depth, and the little offset lifts the pipe that much so it enters straight instead of at an angle.

What angle is a box offset bent at?

A shallow one — often around 10° to 30°, because the rise is small and a gentle angle keeps the jog short and easy to seat. Some benders have a dedicated box-offset tool or a hickey that makes a set small angle; if yours does, enter that angle to match it.

How much rise does a box offset need?

Roughly the depth the box or its raised ring stands off the surface — often a half inch or so. Measure from the surface the pipe runs along to the centre of the knockout, and use that as the offset depth. Too little and the connector cocks; too much and it stands proud.

Does a box offset shrink the pipe?

A little, because it is still an offset. The shrink is small at this depth but the calculator shows it, and on a short tail into the box it is worth adding so the pipe still reaches the knockout cleanly.

Box offset calculator

A box offset is the little step at the end of a run that lets a connector seat square into a box knockout. Enter the small rise to the knockout and the bend angle; the calculator gives the distance between your two marks and the shrink, so the pipe enters straight and still reaches.

Worked example

Say the box stands off the wall a half inch and you make the offset at 22.5°. The 22.5° multiplier is 2.613, so the two marks go 0.5 × 2.613 ≈ 1 5/16 inches apart. The shrink is 0.5 × 0.199 ≈ 1/8 inch — small, but on the short tail into the box worth adding so the connector lands on the knockout. Bend the first mark, then the second the same angle the opposite way, and the pipe steps up level into the box.

The formula

A box offset is an ordinary offset with a small rise, so the same trigonometry applies:

between marks = rise ÷ sin θ · shrink = rise × (1/sin θ − 1/tan θ)

The rise here is just the depth the box stands off the surface. The pipe between the marks is the hypotenuse of the little triangle, rise ÷ sin θ, and the shrink is the same difference between that sloped pipe and the flat run it replaces. Nothing about the box changes the math — it only sets how small the rise is.

Matching a fixed-angle tool

Many box offsets are made with a dedicated tool or a hickey that bends a set angle rather than one you choose. If yours does, read the angle it makes and enter it in the other-angle field, and the marks will match the tool. If you are pulling it on a standard bender, a shallow angle keeps the jog short and the connector easy to seat.

Questions

What is a box offset?: A box offset is a small double bend right at the end of a conduit that steps it up so the connector seats square into a box knockout. The box stands off the surface by its own depth, and the little offset lifts the pipe that much so it enters straight instead of at an angle.
What angle is a box offset bent at?: A shallow one — often around 10° to 30°, because the rise is small and a gentle angle keeps the jog short and easy to seat. Some benders have a dedicated box-offset tool or a hickey that makes a set small angle; if yours does, enter that angle to match it.
How much rise does a box offset need?: Roughly the depth the box or its raised ring stands off the surface — often a half inch or so. Measure from the surface the pipe runs along to the centre of the knockout, and use that as the offset depth. Too little and the connector cocks; too much and it stands proud.
Does a box offset shrink the pipe?: A little, because it is still an offset. The shrink is small at this depth but the calculator shows it, and on a short tail into the box it is worth adding so the pipe still reaches the knockout cleanly.

Related tools

Conduit offset calculator — the full-size version of the same jog.
Conduit shrink calculator — the length even a small offset pulls out.
Conduit bending multipliers — the multiplier for the angle you pick.