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.

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 Measurement X
Y Measurement Y
H Height
DV Divisions
THK Thickness

Worked example

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

Measurement X	600 mm
Measurement Y	200 mm
Height	300 mm
Divisions	16
Thickness	3 mm
The flat pattern fits a plate of	1418 × 300 mm

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.

Oval Tube dimension drawing: the measurements the calculation asks for, marked on the part

Calculate a Oval Tube

An account is required. The free tier covers 20 calculations a month.