Metals vary in weight, but by how much exactly? From Left to right, the image below shows 13 cubes, each exactly one pound (0.45kg). From left to right: Magnesium, Aluminum, Titanium, Tin, Iron, Stainless steel, Brass, Bronze, Silver, Lead, Tungesten, Gold, and Platinum. These cubes were meticulously modeled in SolidWorks using measurements taken from this source.
These two metal cubes appear almost identical, differing only in size. Despite their visual similarities, they are very different in terms of material properties and value.
The left cube is platinum, worth roughly $15,000 a pound. The right cube is magnesium, and is worth only $2 a pound.
Right: Platinum vs Magnesium
Gold and Tungsten are almost identical in weight and size. This is the reason that gold plated tungsten is often used to counterfeit real gold bars.
Right: Gold vs Tungsten
Steel is stronger than titanium, but it is also heavier. When both strength and weight savings are required, the additional cost of titanium over steel (or aluminum, which is cheaper and lighter, but much softer) may be justified.
Right: Steel vs Titanium.