How to use this calculator
- Enter actual ODs. Use measured or schedule outside diameters for both the header and branch pipes.
- Set branch angle. Enter the angle between branch centerline and header centerline, such as 90 degrees for a tee or 45 degrees for a lateral.
- Mark the branch. Divide the branch circumference into 16 equal marks using the reported spacing.
- Transfer drops. Measure template drops from the long point at the 1/8, 1/4, 3/8 and 1/2 marks, mirroring as needed around the branch.
How it works
This saddle layout treats the header and branch as two ideal cylinders
whose centerlines intersect. Let R be header radius,
r be branch radius, beta be the branch angle
from the header axis and theta be the angle around the
branch circumference.
The axial distance from the header centerline to the branch cut curve is:
w(theta) = (-r cos(theta) cos(beta) + sqrt(R^2 - r^2 sin(theta)^2)) / sin(beta)
The wrap-around template uses the long point as zero drop:
drop(theta) = max(w) - w(theta)
Use the pipe miter cut calculator for equal-piece elbows, the pipe bend developed length calculator for smooth bends, the pipe rolling offset calculator for offset spools, the pipe reducer offset calculator for nearby size changes and the steel pipe schedule chart for actual OD, wall and ID.
Worked example
Verified against the live calculator
A centered 90 degree branch with 2 in OD pipe on a 6 in OD header has a long point about 3.00 in from the header centerline and a short point about 2.83 in from the header centerline. The full saddle depth is about 0.172 in. The branch circumference is 6.28 in, so 16-mark spacing is 0.393 in. Drops from the long point are about 0.085 in at the 1/8 mark, 0.172 in at the 1/4 mark, 0.085 in at the 3/8 mark and 0 in at the 1/2 mark.
Frequently asked questions
How do you lay out a pipe saddle cut?
Use actual header and branch outside diameters, divide the branch circumference into equal marks, then calculate the axial drop from the long point at each mark. This calculator uses centered cylinder-intersection geometry for the branch pipe cut.
What angle should I enter for a pipe lateral?
Enter the angle between the branch centerline and the header centerline. Use 90 degrees for a straight tee and 45 degrees for a common lateral branch.
Does this calculate the header hole?
No. It lays out the cut curve on the branch pipe only. Header hole layout, reinforcement, weld prep, weldolet dimensions, inspection and code acceptance are separate shop or project requirements.
Can the branch pipe be larger than the header pipe?
This centered saddle model supports branch OD no larger than header OD. Larger or offset branches need a detailed development drawing or CAD layout.
Method & assumptions
- Uses centered cylinder-intersection geometry; branch and header centerlines intersect.
- Branch angle is measured between branch centerline and header centerline.
- Template drops are for the branch pipe cut, not the header hole.
- Does not calculate offset branches, branch reinforcement, weldolet takeout, weld gap, bevel, backing, flow loss, fit-up tolerance, code acceptance or inspection requirements.