Rolling Offset Calculator
The travel and setback of a rolling pipe offset from its rise and roll, for 45, 22½, 60 or 11¼ degree fittings or any other angle.
Result
28.28 in
Travel is centre to centre; subtract your fittings’ take-off for the cut length.
- True offset
- 20 in (1.67 ft, 508 mm)
- Setback along the run
- 20 in (1.67 ft, 508 mm)
- Travel multiplier for this angle
- 1.4142
https://calcgallery.com/home-systems/rolling-offset-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Rolling Offset Calculator
- Measure the rise, how far the pipe must move up or down, and the roll, how far it must move sideways.
- Choose the angle of the fittings you will use, or enter another angle.
- Read the travel, centre to centre of the two fittings, and the setback, how much run the offset takes up.
The trigonometry
true offset = √(rise² + roll²)travel = true offset ÷ sin(fitting angle)setback = true offset ÷ tan(fitting angle)Once the true offset is known, the rolling offset becomes a simple offset in the plane of the diagonal. The travel is the hypotenuse of the triangle formed by the true offset and the setback, with the fitting angle between the travel and the run.
Choosing a fitting angle
A shallower fitting takes up far more run: at 11¼° the same 20-inch offset needs about 100 inches of setback, against 20 at 45° and under 12 at 60°. The page shows all three quantities so you can check the offset fits the space before cutting.
With your numbers
- True offset = √(rise² + roll²)
- Travel = true offset ÷ sin(fitting angle); setback = true offset ÷ tan(fitting angle)
Quick reference
Travel is centre to centre; subtract your fittings’ take-off for the cut length.
| Job | Travel, centre to centre |
|---|---|
| Rise 12, roll 16 in, 45° | 28.28 in |
| Rise 12, roll 16 in, 22½° | 52.26 in |
| Rise 12, roll 16 in, 60° | 23.09 in |
| Rise 12, roll 16 in, 11¼° | 102.52 in |
| Simple 10 in offset at 45° | 14.14 in |
| Rise 8, roll 6 in, 30° | 20 in |
| Rise 300, roll 400 mm, 45° | 707.11 mm |
Common questions about the Rolling Offset Calculator
- What is a rolling offset?
- An offset that moves a pipe up or down and sideways at the same time, so the diagonal piece is neither level nor plumb. Seen from the end, the rise and the roll are the two sides of a right triangle, and the distance the pipe really shifts, the true offset, is its hypotenuse.
- How do I calculate a 45-degree rolling offset?
- Find the true offset first: √(rise² + roll²). A rise of 12 inches and a roll of 16 is √(144 + 256) = 20 inches. Multiply by 1.414 for 45-degree fittings: the travel is 28.28 inches, centre to centre. The setback, at 45 degrees, equals the true offset: 20 inches.
- Where does the 1.414 come from?
- It is 1 ÷ sin 45°, the ratio of the diagonal to the offset it crosses. Every fitting angle has its own: 2.613 for 22½°, 1.155 for 60° and 5.126 for 11¼°. The page computes it for the angle you choose rather than looking it up.
- Is the travel the length to cut?
- No. The travel runs from the centre of one fitting to the centre of the other. The pipe is shorter by the take-off of each fitting, the distance from its centre to where the pipe seats, which depends on the fitting’s size and make.