This calculator lets you find out how much an item that is a rectangular box ("something that looks like a brick") weights based on its size and density. For example, if you have a brick that has a size of 92 x 57 x 203 millimeters and a density of 2.4 kg/L, you'd find out that the weight of that object is 2.555kg.
Volume and density calculators deal with subsets of this problem. Concrete calculator lets you calculate how many bags of concrete you need. The brick calculator answers the question: how many bricks do I need?.