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Do you have your material set to what you intend to use? solidworks has a built in set of materials you can choose from in the design tree on the left. after choosing a material, click on "file" at the top of the window and the go down to "properties" and it will show you the mass of the block. note that this only works on one file at a time. it looked in your picture that you had two blocks on one part drawing, unless that is just a picture of an assembly and they're sitting side by side.