Do you know how to work out the weight of steel plate?

Length x Breadth x thickness x 7.85 (Specific material density for Mild Steel)
1 metre x .5 metre x 6mm x 7.85 = 23.5 kilograms
1 metre x 1 metre x 10mm x 7.85 = 78.5 kilograms
6 meters x 3 meters x 20 mm x 7.85 = 2,826 kilograms.