Why the same-size ring can feel completely different in the hand
Density is mass packed into a given volume, and it is the reason two rings that look identical can weigh very differently. Platinum is 21.45 grams per cubic centimetre. Pure gold is 19.32. Silver is 10.49, less than half of platinum. Palladium sits in between the precious metals and the base ones at 12.02. None of that is estimated — these are the standard densities published for each element, the same figures used across metallurgy and gemology references, and they do not vary by manufacturer the way an alloy composition can.
The practical consequence: a platinum ring cast from the same mould as a gold one comes out roughly 11% heavier, because the mould fixes the volume and density does the rest. That is also why palladium and titanium rings — at 12.02 and 4.51 g/cm³ — feel noticeably light for their size, and why that lightness is often the first clue that a white ring is not platinum.
The arithmetic behind "what would this weigh in a different metal"
Two objects of identical volume have a mass ratio equal to their density ratio — nothing more complicated than that. If a piece weighs 5 grams in gold and you want to know what the same mould produces in platinum, the answer is 5 × (21.45 ÷ 19.32), about 5.55 grams. The calculator above runs exactly that division for any pair of metals in the table.
The condition that matters is "same mould" — meaning the same volume of metal, not merely the same apparent size. A hollow ring, a piece with thicker walls, or one with a different shank profile changes the volume even when it looks the same size on a finger, and the arithmetic here has no way to see any of that. It compares metal to metal, not photograph to photograph.
Density as a fake-detection tool, and where it breaks
Weighing an item and estimating its volume — commonly by water displacement, a technique called hydrostatic weighing — is one of the few checks a jeweller or a careful buyer can do without damaging a piece, because density is a property of the metal itself and cannot be faked by plating a thin gold layer over something else. A gold-plated tungsten or lead item will weigh markedly wrong for its apparent volume, because plating adds a fraction of a millimetre while the bulk of the object stays base metal.
The one metal that defeats this check is tungsten, at 19.25 g/cm³ against gold's 19.32 — within half a percent. That closeness is not a coincidence buyers stumbled into; tungsten-filled fake gold bars have specifically exploited it, because a bar that weighs almost exactly right for its size passes a casual scale test. Density alone cannot tell tungsten from gold reliably; an assay or an XRF scan can, because those test composition rather than weight.