How the Pipe Cut Length Calculator works
The pipe you cut is shorter than the center-to-center measurement, because each fitting uses up part of that distance. This calculator subtracts both fitting take-outs and the gap at each joint from the center-to-center to give the cut length. A helper also gives the take-out of an elbow cut down to another angle.
Cut length = center to center − take-out A − take-out B − 2 × gap. The take-out is how much of the center-to-center a fitting uses up: center to end for a butt-weld fitting, center to the bottom of the socket for socket weld, and center to face minus the thread engagement for threaded fittings. The gap is per joint: the root gap for butt welds, the back-off for socket welds, 0 for threaded. An elbow cut to angle A has a take-out of radius × tan(A ÷ 2).
Example: 36" center to center between two butt-weld fittings with 3" take-outs and a 1/8" root gap. Cut length = 36 − 3 − 3 − 2 × 1/8 = 29 3/4".
Take-outs differ by size, schedule, fitting type and maker, so measure the fitting or use the maker's dimension sheet; the calculator never looks them up. For an offset, the center-to-center is the travel from the Pipe Offset Calculator. If the take-outs and gaps add up to more than the center-to-center, the calculator says the fittings won't fit.
Frequently asked questions
What is take-out in pipefitting?
The distance from the center of a fitting to the point where the pipe stops inside or against it. Subtracting the take-outs of both fittings from the center-to-center measurement gives the length of pipe to cut.
How do you calculate pipe cut length?
Center to center minus both take-outs minus the gaps. A threaded piece with different fittings at each end and no gap: 24 − 1 3/8 − 7/8 = 21 3/4".
What gap do I leave for a socket weld?
About 1/16" (1.5 mm) between the pipe end and the bottom of the socket before welding, so the joint is not welded bottomed out; ASME B31.1 and B31.3 show this gap. Enter it as the gap per joint, and follow the welding procedure for your job.
What is the take-out of an elbow cut to 45 or 60 degrees?
Radius × tan(angle ÷ 2). With a 3" centerline radius, a 45° cut gives 3 × 0.414 = 1.24" (1 1/4"), a 60° cut 3 × 0.577 = 1.73" (1 3/4"), and the full 90° gives the radius, 3".