Calculate the length of a surface

Is there a way to calculate the length of a surface.

I am trying to find the length of the blue curved plate, as well as the yellow plate!. I was looking into having the project 3D printed or milled out but it is not going to be coast effective, $300.00 for set up and another $300.00 to $500.00 to do the milling . It would have been milled out of aluminum and would be 21/2” long and 2” high.
So this is why I would like to find out the exact length of the pieces. I am going to cut the pieces out of flat stock 6061 aluminum and use low heat welding rods to weld them together.

Draw a midline with the offset tool , then highligt it to blue, and you can see the full length at the bottom of the screen.
Or if you not made the union yet, also you can see the surface area, and the volume