Tube U-Bend Cut Length Calculator
Enter the tube OD, the die centerline radius, finished height, and any end trim allowance. The result gives the rough blank to cut and the three layout marks measured from its first end.
Rough stock cut length (in)26.92
- Finished centerline length (in)
- 26.42
- Finished outside width (in)
- 7
- Straight length per leg (in)
- 8.5
- 180° bend arc length (in)
- 9.42
- First tangent mark (in)
- 8.75
- Bend center mark (in)
- 13.46
- Second tangent mark (in)
- 18.17
All dimensions use the selected unit; changing units does not convert the entered values.
The entered CLR must match the die used, or the calculated outside width will not be achieved.
How to use this calculator
- Choose inches or millimeters and use that same unit for each dimension.
- Enter the actual tube outside diameter and the CLR stamped or specified for the bending die.
- Measure finished overall height from the open ends to the outside of the return.
- Add the stock you intend to keep at each end for gripping, squaring, or final trimming.
- Mark the first tangent, bend center, and second tangent from one rough-cut end before making a test bend.
How to calculate a U-bend cut length
This calculator lays out a symmetric, planar 180-degree return using the tube centerline. The centerline is the path used by a rotary-draw die, so a die’s centerline radius, or CLR, is the radius that matters for this calculation. The tube outside diameter is still needed because the finished height and width are measured on the outside of the tube.
Let D be tube outside diameter, R be die CLR, H be finished overall height, and E be trim allowance at each end. The straight finished length in each leg is:
S = H − R − D ÷ 2
The 180-degree centerline arc is half a circle, so its developed length is B = π × R. The remaining results follow directly:
finished centerline length = 2S + Brough stock cut length = 2S + B + 2Efinished outside width = 2R + Dfirst tangent = E + S,bend center = first tangent + B ÷ 2, andsecond tangent = first tangent + B
The tangent marks identify where the straight centerline meets the bend arc. The center mark is useful when the bender or a layout template uses the middle of the 180-degree bend as its reference. All three marks are measured from the same first end of the rough blank.
Dimensions that change the result most
CLR directly controls both the bend arc and the finished outside width. Increasing CLR by one unit adds π units to the arc and two units to finished width. Height changes only the two straight legs: increasing height by one unit adds two units to the finished centerline length and rough stock length. Tube OD changes the outside dimensions and reduces each straight leg by half its change, while leaving the arc length set by the CLR.
The height must be at least R + D ÷ 2. At exactly that value there are no straight finished legs; the part is a pure 180-degree return. A lower height cannot be made with this geometry because it would require negative straight length.
What this layout leaves out
This is a geometric centerline estimate, not a programmed bender setup. It does not compensate for clamp and draw length, springback, elongation, wall thinning, ovality, or the calibration of a particular machine. The die used must have the entered CLR; a different die produces a different width and arc length. Make and measure a test piece before cutting a production batch, especially for tight bends, thin-wall tube, or critical assemblies.
Worked example
For 1.000 in OD tube bent on a 3.000 in CLR die to a 12.000 in finished overall height, with 0.250 in trim allowance at each end, the straight length per leg is 12.000 − 3.000 − 1.000 ÷ 2 = 8.500 in. The bend arc is π × 3.000 = 9.425 in.
The finished centerline length is 2 × 8.500 + 9.425 = 26.425 in, and the rough stock length is 26.925 in after adding 0.500 in total trim. Finished outside width is 2 × 3.000 + 1.000 = 7.000 in. From the first rough-cut end, mark the first tangent at 8.750 in, bend center at 13.462 in, and second tangent at 18.175 in.
Common questions
What is centerline radius in tube bending?
Centerline radius is the radius from the bend center to the center of the tube wall. Rotary-draw dies are commonly specified by CLR, and that is the radius used for the 180-degree arc in this calculator. It is not the inside radius or outside radius of the finished tube.
How do I calculate the tube needed for a U-bend?
Find each straight leg from finished height, then add the 180-degree centerline arc. For a symmetric U-bend, the arc is pi times the die CLR and the finished centerline length is twice the straight leg plus that arc. Add any planned trim allowance at both ends to determine rough stock length.
Where should I mark a 180-degree tube bend?
Measured from one rough-cut end, the first tangent mark is the trim allowance plus one finished straight leg. Add half the bend arc to get the bend-center mark, then add the full bend arc to the first tangent to get the second tangent. Confirm which reference mark your specific bender uses before bending.
How wide will a U-bend be with my die?
The finished outside width is twice the die CLR plus the tube outside diameter. A 3 inch CLR die bending 1 inch OD tube makes a 7 inch outside width. A die with another CLR cannot make that same width without changing the geometry.
Does wall thickness change the developed length?
This calculator uses the die centerline, so wall thickness is not an input to its geometric arc length. Wall thickness can still affect whether the bend is practical and how much springback, thinning, or ovality occurs. Use a test bend and the tooling supplier’s limits when those effects matter.
How much extra tube should I leave for trimming?
Leave enough at each end for your clamp, saw cut, squaring process, and final part tolerance. Zero is valid when no extra stock is needed, in which case rough and finished centerline lengths match. The right amount is machine- and process-specific, so prove it on a sample part before a batch.