Roofing & Exterior
Ramp Calculator
Work out ramp length, slope angle and landings from the total rise and slope ratio.
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Plumbing & Layout
Rolling Offset Formula
A rolling offset moves a pipe both up and over at once. Enter the rise and roll and choose your fitting angle to get the travel (centre-to-centre) length to cut.
What is a rolling offset?
In plumbing and pipe fitting, a rolling offset changes a pipe’s position in two directions with one pair of fittings. This tool gives the three numbers you need: the true offset, the travel between fitting centres and the setback along the run.
How does it work?
The rise and roll form two sides of a right triangle; their hypotenuse is the true offset. Multiplying the true offset by the constant for your fitting angle gives travel, and a second constant gives setback. The same right-triangle maths drives the Ramp Calculator.
What information is needed?
- Rise — vertical distance between pipe centrelines
- Roll — horizontal distance between centrelines
- The angle of the fittings you will use
How to use the Rolling Offset Formula
- Measure rise centre-to-centre with a level.
- Measure roll centre-to-centre square to the pipe run.
- Choose the fitting angle.
- Select Calculate, then deduct fitting take-offs to get the cut length.
The formula
In plain terms, here is the calculation the tool runs:
True offset = √(Rise² + Roll²)
Travel = True offset × Constant
Setback = True offset × Setback constant
- 45°
- Travel 1.414 · Setback 1.000
- 60°
- Travel 1.155 · Setback 0.577
- 22½°
- Travel 2.613 · Setback 2.414
- 11¼°
- Travel 5.126 · Setback 5.027
Worked example
Example
A 12" rise and 16" roll with two 45° fittings.
- √(12² + 16²) = √400 = 20"
- 20 × 1.414 = 28.28" travel
- 20 × 1.000 = 20" setback
Travel is 28 5/16" centre to centre.
Frequently asked questions
What is fitting take-off?
The distance from the centre of a fitting to the end of the pipe inside it. Subtract it for each fitting from travel.
Why is it called rolling?
Because the offset is not in one plane — the pipe “rolls” around the run as it rises.
Can I use this for conduit?
The geometry is the same for conduit bends, though electricians often use multipliers based on bend angle.
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