FitUp

Tool 02 · Rolling offset

Rolling offset calculator for iPhone, from rise and roll to cut length

A rolling offset moves the line up and over at the same time. FitUp's rolling offset tool takes the rise and the roll, finds the true offset, and gives the travel, the run, and the cut length with take-outs and gaps off, drawn as the box the pipe passes through.

What the rolling offset tool does

  1. Type the rise and the roll

    Rise measured plumb and roll measured level, both centerline to centerline.

  2. Pick the angle, pipe size, and fitting

    The same choices as the simple offset tool, with the take-out and gap from your settings.

  3. Tap Calculate

    FitUp shows the true offset, the travel, the run (setback), both take-outs, both gaps, and the cut length, with every formula line under them.

The box diagram labels the rise, the roll, and the run, and draws the travel corner to corner, so you can see which way the fittings turn before you tack anything.

FitUp rolling offset screen: an 8 inch rise and 16 inch roll drawn as a box, true offset 17 7/8, cut length 22 5/16, travel 25 5/16, run 17 7/8, and the formula lines
Rise 8, roll 16, at 45 degrees on 2 inch pipe: true offset 17 7/8, cut 22 5/16.

Travel and run for a rolling offset: an example

An 8 inch rise and a 16 inch roll with 45 LR elbows on 2 inch pipe and a 1/8 inch gap:

True offset = √(8² + 16²) = 17.8885 Travel = 17.8885 ÷ sin 45° = 25.2982 Run = 17.8885 ÷ tan 45° = 17.8885 Cut = 25.2982 − 2 × 1.375 − 2 × 0.125 = 22.2982, marked 22 5/16

The rolling offset formula guide walks through each line and how to measure the rise and roll on the job.

Setback mode: when the run is fixed

Sometimes the run is the number you cannot change: a wall, a column, a valve that is already set. In setback mode you type the rise, the roll, and the setback you have room for, and FitUp works out the fitting angle ("Fitting angle comes out of the box: 22.6°") and the travel as the square root of true offset squared plus setback squared. A 3 inch rise and a 4 inch roll in a 12 inch setback give a 5 inch true offset, a 13 inch travel, and a 22.6 degree fitting angle. Setback mode is part of Pro.

What is free

Ten rolling offsets at 45 degrees each calendar month are free, with the full answer. The line "N of 10 free rolling offsets left this month" sits above the inputs and on the home screen tile, and the count resets on the 1st. Only a calculation you can read spends one; a blurred answer at another angle does not. Pro removes the limit, opens every angle, and adds setback mode.

No phone handy? The free rolling offset calculator on this site uses the same math.