FitUp

Tool 01 · Simple offset

Simple offset calculator for iPhone, from offset to cut length

The simple offset tool in FitUp turns one measurement into the length you cut. Type the offset, pick the angle, the pipe size, and the fitting, and read the travel, the run, both take-outs, both gaps, and the cut length to the nearest 1/16 inch.

What you type

  • Offset, center to center. Whole inches plus sixteenths on a picker, or decimal inches if you set decimals.
  • Fitting angle. 11.25°, 22.5°, 30°, 45°, 60°, or Custom, from 1 to 89 degrees.
  • Pipe size. 1/2 to 12 inch.
  • Fitting. At 45 degrees: 45 LR butt-weld, threaded or socket-weld 45s (once you have entered take-outs for them), or none, center to center. At any other angle: a 90 LR or 90 SR cut down to that angle, or none.

What you get back

  • Cut length in green, rounded once to the nearest 1/16.
  • Travel, fitting center to fitting center, and run, how far the offset advances along the line.
  • Take-outs as 2 × the center-to-end, with the line "Default values. Check your fittings."
  • Gap as 2 × the root gap, for butt-weld fittings.
  • The formula with exact decimals, for example Travel = 20 ÷ sin 45° = 28.2843, and the multipliers for the angle.
  • The offset triangle, drawn to the angle with each side labeled.
FitUp's hands-on first offset: 20 inches at 45 degrees on 2 inch pipe, cut length 25 5/16 inches, travel 28 5/16, run 20, take-outs 2 x 1 3/8, gap 2 x 1/8, with the formula lines
20 inch offset, 45 degrees, 2 inch pipe, 45 LR elbows, 1/8 gap: cut 25 5/16.

A worked example: 10 inch offset on 2 inch pipe

A 10 inch offset with two 45 LR butt-weld elbows on 2 inch pipe and a 1/8 inch root gap:

Travel = 10 ÷ sin 45° = 14.1421 Run = 10 ÷ tan 45° = 10 Cut = 14.1421 − 2 × 1.375 − 2 × 0.125 = 11.1421, marked 11 1/8

The take-out, 1 3/8 inch, is the published center-to-end of a 2 inch 45 LR elbow. If your elbows measure differently, Pro lets you change the value once and every offset after that uses it. The full method is in how to calculate a 45 degree offset.

When the fittings will not fit

Two elbows need room. On 6 inch pipe, two 45 LR elbows take out 3 3/4 inch each, and with two 1/8 inch gaps a 4 inch offset leaves no pipe at all. Instead of a negative cut length, FitUp shows "Too short for two 6 in 45 LR fittings" and the shortest offset that leaves 1/16 inch of pipe between them, which is 5 9/16 inch here.

Offsets at 22.5, 30, 60, and 11.25 degrees

At any angle other than 45, the fitting is a 90 cut down to the angle, so FitUp works out its take-out as the 90's center-to-end times the tangent of half the angle. A 2 inch 90 LR (3 inch center-to-end) cut to 22.5 degrees takes out 0.597 inch, about 5/8. For a 12 inch offset at 22.5 that gives a travel of 31 3/8 and a cut of 29 15/16 with 1/8 gaps. The cut-down elbow guide explains the formula.

On the free tier, picking one of these angles still draws the diagram; the travel, run, and cut length sit behind a panel that reads "See the cut for 22.5 degrees", with a button to the Pro plans. Every 45 degree offset stays free.

For plumbing: center to center

If you pick plumbing during setup, FitUp starts with no fittings and no gap, and gives the center-to-center travel: 14 1/8 inch for a 10 inch offset with 45s. Make-up differs between threaded, sweat, and glued joints, so the app does not guess. With Pro you can type your own threaded take-outs in the chart and get a cut length instead.

Try the same math in the browser with the free pipe offset calculator, or see the multipliers for every angle in the offset multiplier chart.