Rolling offset calculator

A rolling offset moves a conduit over and up (or down) at the same time. Instead of two separate offsets, you bend one offset whose depth is the diagonal of the rise and the roll — the true offset — with the conduit rolled to the right angle.

Last reviewed Nov 14, 2026 · Sources at the end of the page

The rolling offset formula

True offset = √(rise² + roll²)
Distance between bends = true offset × multiplier
Shrink = true offset × shrink per inch
Roll angle = arctan(roll ÷ rise)

It's the Pythagorean theorem: the rise and roll are the two sides of a right triangle and the true offset is the hypotenuse. IBEW Local 903's Bending Book works it the same way (its example: 4″ and 3″ give a 5″ offset) and adds a field shortcut — mark the rise and the roll on a framing square and measure diagonally between the two marks. Then bend the true offset as an ordinary offset.

Worked example: 8″ rise, 6″ roll, 30° bends

1. True offset: √(8² + 6²) = √100 = 10″.
2. Distance between bends: 10 × 2.00 = 20″.
3. Shrink: 10 × ¼″ = 2 1/2″.
4. Roll angle: arctan(6 ÷ 8) ≈ 36.9° from vertical.
5. Mark and bend as a 10″ offset with the conduit rolled about 37° off vertical.

Quick true-offset table

Setting the roll in the field

Mark the conduit's top centerline, then rotate it by the roll angle before the first bend. A torpedo level with an angle vial or an angle finder on the conduit gets you close; a full 45° roll is exactly halfway between vertical and horizontal. Keep the second bend in the same plane as the first.