Why can X and Y not be equal?

If they were, the straight runs would vanish and the part would become a cylinder — which has its own, more direct calculation.

Is the plate length the section perimeter?

Yes, taken on the neutral axis: the two semicircles add up to one full circumference, plus twice the straight run.

How do I calculate the ovality of a round pipe?

Ovality (%) = (Dmax − Dmin) / Dnom × 100, measured in one cross-section. That is the unwanted out-of-roundness of a pipe meant to be round; this page is the designed oval section. The formula, a worked example and the code limits are in the pipe ovality guide, linked below.

Oval Tube flat pattern

What it is

The oval, or obround, tube has a section made of two semicircles joined by two straight runs. It is the easiest shape to form after the circle, because there are only two radii and they are equal.

Where it is used

Flattened ventilation ducting, under-floor runs, light structural sections, handrails and guards.

Measurements the calculation needs

X Width of the section (larger measure)
Y Height of the section (diameter of the semicircles)
H Length of the tube
DV Divisions
THK Plate thickness

Calculate with your own measurements

No account needed: enter the measurements in millimetres or inches and get the figures and the drawing. The scaled PDF template, the DXF for the cutting table and the 3D model take a free account.

Diameters and sides are outside measurements. The flat pattern already allows for the plate thickness, working on the mean line.

Inches or millimetres? mm inches

Worked example

The values the form comes pre-filled with, run through the tool itself:

Width of the section (larger measure)	600 mm
Height of the section (diameter of the semicircles)	200 mm
Length of the tube	300 mm
Divisions	16
Plate thickness	3 mm
The flat pattern fits a plate of	1419 × 300 mm

Result of the example

Plate	1419 × 300 mm
Area and weight	0.43 m² · ≈ 10.0 kg in 3 mm steel

Oval Tube flat pattern: drawing of the template with the worked example dimensions — Cut lines in purple, welds in green and reference lines in orange. Plate 1419 × 300 mm.

Guides about this part

Frequently asked questions

Why can X and Y not be equal?: If they were, the straight runs would vanish and the part would become a cylinder — which has its own, more direct calculation.
Is the plate length the section perimeter?: Yes, taken on the neutral axis: the two semicircles add up to one full circumference, plus twice the straight run.
How do I calculate the ovality of a round pipe?: Ovality (%) = (Dmax − Dmin) / Dnom × 100, measured in one cross-section. That is the unwanted out-of-roundness of a pipe meant to be round; this page is the designed oval section. The formula, a worked example and the code limits are in the pipe ovality guide, linked below.

Oval Tube dimension drawing: X (Width of the section (larger measure)), Y (Height of the section (diameter of the semicircles)), H (Length of the tube), DV (Divisions), THK (Plate thickness), marked on the part

Calculate here, no account Open the full calculator

You can work out the figures right here, with no account. PDF, DXF, 3D and history take an account — free, with unlimited calculations.