Rolling Offset Calculator: Takeout, Weld Gap & Cut Length

Q: Is a rolling 45 calculator free in FitterMaster?

Yes. The Offset calculator at the 45° fitting angle, with takeouts and cut length, is free. Other angles need the one-time Pro purchase.

A rolling offset moves the line in two directions at once: up or down (the set, or rise) and sideways (the roll). Two fittings at the same angle carry the pipe diagonally across that box, and the length of pipe between them is what you need to cut.

You meet them all the time on racks and in plant rooms: jumping over a line while also stepping out to clear a column, or dropping into a header that sits off to one side. The 15" × 8" example below has been checked against the math before trusting the number here.

Enter rise, roll and fitting angle

Rolling offset calculator

Takeout Weld gap Cut

Travel (center to center): 2'-0-1/16"
Cut length: 1'-9-5/16"
True offset: 1'-5"
Takeout per fitting: 1-3/8"
Run: 1'-5"
Multiplier: ×1.4142

Showing the worked example. Turn on JavaScript to calculate your own numbers.

Same math as the app: true offset = √(set² + roll²), travel = true offset ÷ sin(angle), run = true offset ÷ tan(angle), cut length = travel − 2 × takeout − 2 × weld gap. Both fittings are at the same angle. Measure center to center. The app looks up the takeout for your pipe size and elbow radius.

Type Set (rise) and Roll (0 = simple) in feet, inches and fractions (3' 2 5/16" or plain 3/8 both work), or switch to mm. Pick the Fitting Angle, then choose where the takeout comes from: automatically from the B16.9 table, for the pipe size and the Series, LR or SR, you pick, or a value you type yourself. Add a weld gap per joint if you leave one.

Open Offset under Calculate on the main screen.
Enter Set (rise) with the ft, in and 16ths steppers, then enter Roll (0 = simple).
Under Fitting Angle, keep 45°. The other angles are Pro, as the note 45° is free — unlock all angles with Pro. says.
Under Fitting, choose the pipe Size and the Series, LR or SR. The app looks up the takeout automatically, the same table the calculator above uses.
Set Weld Gap (per joint). It starts from the Default Weld Gap you chose in Settings.
Read the Cut List. The note under it shows the multiplier, and the diagram above labels Set, Run, Travel and the angle.
Tap Copy or Share to pass the numbers on, or with Pro tap Save to keep the result in My Spools.

The screen reopens with your last set, roll, angle, size and series, so you can come back to a job without retyping.

Travel versus actual cut length

True offset = √(set² + roll²). This is the diagonal of the box, the offset you would have if you turned the fittings to lie in one plane.
Travel (center-to-center) = true offset × multiplier, where the multiplier is 1 ÷ sin(fitting angle).
Run = true offset ÷ tan(fitting angle): how far along the line the offset takes.
Cut length = travel − 2 × takeout − 2 × weld gap.

Travel is center to center of the two fittings. Each fitting eats part of that distance between its center and its welding face, the takeout, and the weld gap you leave at each joint takes a little more. Forget either and the spool comes out too long.

The takeout is the center-to-face of each fitting. For 45° long-radius ells it comes from the ASME B16.9 table (1.38" on a 2" ell); for other angles FitterMaster works it out from the elbow radius, R × tan(angle ÷ 2). The calculator above does the same lookup automatically when you leave the takeout on the B16.9 table, or you can type your own value instead.

Worked example with weld gaps

45°, with and without a weld gap

Set 15", roll 8", 2" long-radius 45° ells. A 1/16" weld gap at each joint shortens the cut by 1/8" total against no gap at all:

FitterMaster Cut List, 15" set × 8" roll, 45°, 2" LR
Result	No weld gap	1/16" weld gap (each joint)
True Offset	1'-5"	1'-5"
Travel (c-to-c)	2'-0-1/16"	2'-0-1/16"
Takeout (each)	1-3/8"	1-3/8"
Cut Length	1'-9-5/16"	1'-9-3/16"

How: true offset = √(15² + 8²) = 17.0000", travel = 17 × 1.4142 = 24.0416". Cut length = travel − 2 × takeout − 2 × weld gap: with no gap, 24.0416 − 2 × 1.38 = 21.2816" (1'-9-5/16"); with a 1/16" gap at each joint, 24.0416 − 2 × 1.38 − 2 × 0.0625 = 21.1566" (1'-9-3/16").

In millimetre mode (Pro), the no-gap job reads 432.0 mm true offset, 610.5 mm travel and 540.5 mm cut length.

22.5°, with a weld gap

Flatter fittings stretch the offset out. With Pro, the same screen handles 5.625°, 11.25°, 22.5°, 30°, 60° and 90°. Example: set 2'-0", roll 10", 3" LR at 22.5°, 1/16" weld gap at each joint.

FitterMaster Cut List at 22.5°, 1/16" weld gap each joint
Result	Value
True Offset	2'-2"
Travel (c-to-c)	5'-7-15/16"
Run	5'-2-3/4"
Takeout (each)	0-7/8"
Cut Length	5'-6"

The multiplier here is ×2.6131. The 22.5° takeout is 1.5 × 3 × tan(11.25°) = 0.8951", the center-to-face of a 3" long-radius ell cut down to 22.5°.

Calculate in feet, inches and fractions

The calculator above reads lengths the way a tape does: whole feet and inches with a fraction, such as 3' 2 5/16", 2-5/16, or a plain fraction like 3/8. Decimals work too (15.5 or 15,5). Switch Units to mm for metric, and typed values convert automatically.

Results round to the nearest 1/16" in inch mode, or 0.5 mm in metric, the same precision FitterMaster itself uses (1/32" is also available in the app's Settings).

Measure set and roll center-to-center of the pipes, not outside to outside.
Do not multiply the set alone. On a rolling offset the multiplier goes on the true offset.
A roll of 0 turns this into a simple offset, and the true offset equals the set.
Real fittings vary within tolerance. If your ells measure different from the table, adjust before you cut.
The cut length does not include saw kerf or bevel allowance.

Use the calculator offline on iPhone

The calculator above runs the same formulas as FitterMaster, so you can check a rolling offset from a browser before you ever open the app. On the job, with no signal, Offset in FitterMaster does the identical math on your iPhone, with the B16.9 takeout and your weld gap built in.

The Offset calculator at the 45° fitting angle, with takeout and cut length, is free. The other fitting angles (5.625°, 11.25°, 22.5°, 30°, 60° and 90°), Odd-Angle Cut, Miter, the full Takeout Chart, saved spools and millimetre mode are part of the one-time FitterMaster Pro purchase.

Questions and answers

What is the formula for a rolling offset?

True offset = √(set² + roll²), travel = true offset ÷ sin(angle), and cut length = travel minus two takeouts and two weld gaps. At 45° the multiplier is 1.4142.

Is a rolling 45 calculator free in FitterMaster?

Yes. The Offset calculator at the 45° fitting angle, with takeouts and cut length, is free. Other angles need the one-time Pro purchase.

Can it do two parallel rolling offsets?

It solves one offset at a time. For parallel lines, run each line through the calculator with its own set and roll.

What does Run mean on the result?

It is how far the offset advances along the original direction of the line, center to center. At 45° it equals the true offset.

Does the calculator account for weld gap?

Yes. Enter a weld gap per joint and it subtracts it twice, once per fitting, from the travel along with the takeout. Leave it at zero if you do not leave a gap.

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Rolling offset calculator with takeout and weld gap