An example of how "Irregular Shape" mode works.
Here's the top plate from my H4 Alien 680mm quadcopter frame. It's a fairly complicated shape. It would be difficult to estimate what that exact piece would weigh if it was cut from a different material. This is where dCal comes in handy.
As you can see, the original piece weighs 65 grams. Its made from 1.5mm carbon fiber plate with a matte finish on both sides. The material looks exactly like the 1.5mm carbon fiber plate I bought from GetFPV. The thickness measures exactly the same.
In dCal, I clicked "New Part" and selected "Irregular Shape" mode. I selected 1.5mm Carbon Fiber plate from the Materials drop-down menu. I entered 65 in the weight field, gave my part a name, and clicked "Save".
Once the part is saved, the original material's unit weight is locked in the database. Now I can open the part again and select ANY other material from the drop-down menu and dCal will calculate what the piece would weigh if it was made from the selected material.
I duplicated the part a few times so you could see the results side by side. The second example shows the weight if I made the exact same piece, with all of the holes and cutouts, using 1/16" carbon fiber plate from Dragonplate instead of the original material. The material from Dragonplate has a textured surface instead of a smooth matte finish but its lighter even though its slightly thicker! (1/16" = 1.59mm).
The next example shows the weight if I made the same piece from Dragonplate's 1/32" (0.8mm) carbon fiber plate. For this one, I selected a matte finish on one side. The other side still has the textured surface but you're only going to see one side anyway.
The fourth example shows the weight if I made the same piece out of 1/16" birch plywood. It would weigh less than half of the original! I frequently use this birch plywood for prototyping new frame designs because its inexpensive and easy to cut. For this particular application, I'd go with the Dragonplate 1/32" carbon fiber.
If you're logged into dCal, you can select any of those pieces and try different materials in the drop-down menu.
By the way, any time you need to convert back and forth between inches and millimeters, you can click the menu in the top right corner. It has fractional buttons too!