How to Calculate total amount of material from BOM?

Hello, how to calculate whole amount of material in Solidworks from BOM? For example, you can easily get overall length of weldment. But what about Sheet metal? 
In example attached, I used one part as weldment, with different material thicknesses, and other is single sheet part.
What is the most common method to get overall Material amount? example: sqm, weight and etc.

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