Bending Reference
Rolling Offset Calculator
Find the true offset, mark spacing, roll angle, and shrink for a rolling offset in EMT. The right-triangle formula, a rise-and-roll chart, and the interactive calculator with an SVG diagram.
The Rolling Offset Formula
A rolling offset is a normal offset pointed in a diagonal direction. You solve it in three steps: find the true offset, apply the offset multiplier, then rotate the pipe by the roll angle so it travels the right way.
Mark spacing = true offset / sin(bend angle)
Roll angle = arctan(roll / rise)
The bend angle (how sharp each of the two bends is, usually 30°) is different from the roll angle (how far you spin the conduit between bends). Shrink follows the true offset, the same as a straight offset.
Rolling Offset Chart
True offset, mark spacing at the two common bend angles, and the roll angle for common rise-and-roll combinations. Mark spacing = true offset / sin(angle).
| Rise | Roll | True Offset | Marks @ 30° | Marks @ 45° | Roll Angle |
|---|---|---|---|---|---|
| 3" | 4" | 5" | 10" | 7.07" | 53° |
| 4" | 4" | 5.66" | 11.31" | 8" | 45° |
| 5" | 5" | 7.07" | 14.14" | 10" | 45° |
| 6" | 4" | 7.21" | 14.42" | 10.2" | 34° |
| 6" | 6" | 8.49" | 16.97" | 12" | 45° |
| 8" | 6" | 10" | 20" | 14.14" | 37° |
Calculate Your Rolling Offset
Enter your rise, roll, and bend angle for exact marks, true offset, and shrink with an SVG diagram. The calculator also handles straight offsets, saddles, 90s, and kicks.
Worked Example: 4-Inch Rise, 4-Inch Roll at 30 Degrees
Given: Conduit must move up 4 inches and over 4 inches to meet a box, using 1/2" EMT and 30-degree bends.
Step 1: True offset. √(4² + 4²) = √32 = 5.66 inches.
Step 2: Mark spacing. 5.66 / sin(30°) = 5.66 × 2.0 = 11.31 inches between the two marks.
Step 3: Roll angle. arctan(4 / 4) = 45°. Rotate the conduit 45 degrees between the first and second bend so the offset travels on the diagonal.
Result: Two 30-degree bends 11.31" apart, rolled 45°, with about 1.4" of shrink (5.66 × 1/4").
Frequently Asked Questions
How do you calculate a rolling offset?
A rolling offset combines a vertical rise and a horizontal roll into one offset. First find the true offset (the straight-line distance the conduit actually travels) with the right-triangle formula: true offset = square root of (rise squared + roll squared). Then treat it like a normal offset: mark spacing = true offset divided by the sine of your bend angle (multiply by 2.0 at 30 degrees). For a 3-inch rise and 4-inch roll, true offset = square root of (9 + 16) = 5 inches, and at 30 degrees the marks are 5 x 2.0 = 10 inches apart.
What is the true offset in a rolling offset?
The true offset is the actual straight-line distance between the start and end of the offset, accounting for both the rise (vertical) and the roll (horizontal). It is the hypotenuse of a right triangle whose legs are the rise and the roll: true offset = square root of (rise squared + roll squared). You always bend to the true offset, not to the rise or roll alone, or the conduit will not land where you need it.
What is the roll angle in a rolling offset?
The roll angle is how far you rotate the conduit around its own axis between the two bends so the offset travels in the correct diagonal direction. It equals the arctangent of roll divided by rise. For a 3-inch rise and 4-inch roll, the roll angle is arctan(4/3) = about 53 degrees from vertical. The bend angle (how sharp each bend is, such as 30 degrees) is separate from the roll angle (which direction the offset points).
When do you use a rolling offset?
You use a rolling offset when the conduit has to change position in two directions at once, for example moving up and over to meet a box that is both higher and off to the side. Instead of making a separate vertical offset and horizontal offset, one rolling offset handles both in two bends. It is common on conduit racks, in mechanical rooms, and anywhere pipe transitions between planes that are not square to each other.
Does the rolling offset shrink the conduit?
Yes, the same as a normal offset. Shrink is based on the true offset and the bend angle: multiply the true offset by the shrink-per-inch constant for the angle (1/4 inch per inch at 30 degrees). For a 5-inch true offset at 30 degrees, shrink = 5 x 1/4 = 1.25 inches. Subtract that when measuring from a reference point so the finished run lands in the right spot.
More Bending References
Conduit Bending Calculator
All 7 bend types with interactive SVG diagrams and verified bender profiles.
Offset Multiplier Chart
Multipliers and shrink per inch for 10° through 60° offset bends.
Conduit Shrink Calculator
Shrink per inch of offset and kick by angle, and why pipe size does not change it.
Saddle Bend Calculator
3-point and 4-point saddle marks, spacing multipliers, and shrink.