# Surface area of Rectangular / Round transition

#### tibor

Hello,

This is my first post on this forum. I am creating an excel spreadsheet that will calculate me the weights of sheet metal HVAC ductwork and I am creating the equations for weight myself. I have some equations which I cannot figure out.

For calculation of weight I need the surface area.

I need to calculate the surface are of rectangular to round transition when I have these parameters:
rectangular base - a x b
diameter of upper round base (frustum) - d
- perpendicular length between base plane (a x b) and truncated plane (d) - l

- there are three types of these transitions, first one is symmetrical, where the center of round base is symmetrical with the center of rectangular base - in this picture the base is square, but I need rectangular base.

-or there may be some offset of upper round base from the center of lower base (asymmetrical transition)

- 3rd type is when the round base is adjacent to the line going up from one side of lower base (axb) (perpendicular transition).

Thank you very much.

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#### nishith

• 1 person

#### trustmeasfrnd

can some one give formula for above case