How to use this calculator
- Measure center-to-center. Between the two fitting centerlines (or to the pipe end where one side has no fitting).
- Pick the end fittings. The calculator pulls each B16.9 takeout for the selected NPS; use custom for valves and non-standard items.
- Set the root gap. Per the WPS — commonly 3 mm (1/8 in) per open-root butt joint, zero at plain ends.
- Cut and verify. Mark the cut length, cut square, and dry-check the spool against the takeouts before beveling and fit-up.
How it works
Pipefitting math runs on takeouts. A drawing or field measurement gives distances between fitting centerlines; the pipe you actually cut spans only the gap between fitting faces. Each fitting's center-to-face dimension — its takeout — comes straight from ASME B16.9, and the cut is what remains:
cut = CTC − TO₁ − TO₂ − Σ root gaps
The famous one is the 90° long-radius elbow: takeout = 1.5 × NPS, exactly, from NPS 1 up (below that the standard holds a 38 mm minimum). The 45° elbow, tee run and cap values are tabulated — this calculator carries the B16.9-2018 numbers for NPS ½ through 24, and the full table lives on the fitting takeout chart.
Upstream of the cut: the rolling offset calculator turns set/run/roll into the travel and angles, and the miter cut calculator covers the cases you fabricate instead of fit. Downstream, the heat input calculator keeps the welds inside the WPS.
Worked example
Verified against the live calculator
An NPS 2 spool measured 1,000 mm center-to-center between
two 90° LR elbows, open-root welds with 3 mm gaps:
cut = 1,000 − 76 − 76 − (3 + 3) = 842 mm
Swap one end for a 45° elbow and the deduction changes to
76 + 35 + 6 = 117 mm → an 883 mm cut. Make one end a plain
field cut (no fitting, no weld) and only one takeout and one gap apply.
The arithmetic is trivial; the craft is using the right takeout
— which is why the chart page exists and why valves always come from the
manufacturer sheet via the custom end.
Frequently asked questions
What is a fitting takeout?
The center-to-face dimension a fitting "takes out" of a measured run: from the fitting centerline to the face you weld the pipe to. For ASME B16.9 long-radius 90° elbows the takeout is 1.5 × NPS (76 mm for NPS 2); 45° elbows, tee runs and caps have their own tabulated values.
How do I calculate pipe cut length from center-to-center?
Cut length = center-to-center − takeout(end 1) − takeout(end 2) − root gap at each welded joint. For an NPS 2 spool measured 1,000 mm between two 90° LR elbow centerlines with 3 mm gaps: 1,000 − 76 − 76 − 6 = 842 mm.
What is the takeout of a 45 degree elbow?
The B16.9 center-to-face B: 35 mm for NPS 2, 64 mm for NPS 4, 95 mm for NPS 6 — close to 0.625 × NPS for larger sizes. Note this is the centerline takeout; in an offset, the 45° centerline distances come from the travel/run geometry first.
Do these takeouts apply to socket-weld or threaded fittings?
No. This page covers ASME B16.9 butt-weld fittings. Socket-weld and threaded fittings (B16.11) have different engagement-based takeouts, and valves and flanged equipment use the manufacturer's face-to-face dimensions — enter those with the custom end.
Method & assumptions
- Takeout data: ASME B16.9-2018 Tables 6.1-1 (LR elbows), 6.1-7 (tee run) and 6.1-10 (caps), NPS ½–24; center-to-end tolerance ±2 mm in that range.
- Straight spool between two fittings measured on the centerlines; offsets need their travel geometry solved first.
- Butt-weld fittings only; socket-weld/threaded engagement and valve/flange face-to-face dimensions use the custom end.
- Root gap per the governing WPS; thermal cutting kerf and end-prep stock are not included in the cut length.