Rolling Offset Calculator

A rolling offset changes elevation and horizontal position at the same time — for example, running conduit up a wall while also shifting sideways around a column, all in one fitting-free run. It is an offset bent in two planes at once, which is why flat offset math alone will not get you there.

The true offset formula

First combine the vertical rise and the horizontal roll into a single number, the true offset:

True offset = √(rise² + roll²)

Example: 6" of rise with 8" of roll gives √(36 + 64) = 10" of true offset. From here it works like a regular offset: mark spacing = true offset × multiplier. At 30°: 10 × 2.0 = 20" between marks.

The rotation angle

After the first bend, you roll the bender (and the conduit) before making the second bend, so it lands in the correct plane. The rotation angle is:

Rotation = arctan(roll / rise)

For 6" rise and 8" roll: arctan(8/6) ≈ 53.1°. Mark the rotation line on the conduit so the second bend goes in exactly the right plane — this is the step most people get wrong on their first rolling offset.

Shrink on a rolling offset

Shrink applies to the true offset, not the rise or roll alone. A 10" true offset at 30° loses 10 × 1/4" = 2.5" of run length. Add it to your total before cutting.

Field tips

• Sketch the rise-vs-roll triangle on the conduit or a scrap of drywall before you bend. Seeing the triangle keeps the two dimensions honest.
• Rolling offsets magnify small angle errors — verify the first bend's angle before committing to the second.
• Sanity check: when rise equals roll, the rotation angle is exactly 45°.
• If the rotation feels awkward to hold, bend the offset in the flat plane first and rotate the whole assembly into place only if the run allows it — but the math above is what keeps both ends where the plan says they go.