Osmium (Os, atomic number 76) has a density of 22.587 g/cm3 at 20°C, equal to 22,587 kg/m3, per Wikipedia's element data, a CRC/Arblaster-derived crystallographic value. That figure makes osmium the densest of all naturally occurring elements at ordinary pressure, narrowly ahead of iridium, and it is the single number every conversion, ranking and comparison on this page is built from.
How Dense Is Osmium?#
Osmium's density of 22.587 g/cm3 at 20°C, equal to 22,587 kg/m3, makes it the densest of the six platinum group metals, a modern X-ray crystallographic value rather than an older bulk measurement, a distinction covered in full further down this page. Osmium belongs to the platinum group metals (PGMs), and its full identity and history sit on this site's own osmium (Os), element 76 page.
Symbol: Os · Atomic number: 76 · CAS: 7440-04-2
Osmium Density in Other Units#
The table below converts osmium's 22.587 g/cm3 density into the units buyers, engineers and students ask for. Every column is arithmetic on that single figure, using the standard conversions 1 g/cm3 = 1,000 kg/m3 = 0.036127 lb/in3 = 0.57804 oz/in3 = 1 g/mL exactly.
| g/cm3 | kg/m3 | lb/in3 | oz/in3 | g/mL |
|---|---|---|---|---|
| 22.587 | 22,587 | 0.8160 | 13.0562 | 22.587 |
A cubic inch of osmium (16.387 cm3) therefore weighs about 370 g, or 0.816 lb, considerably more than the same volume of almost any other material.
Where Osmium Ranks Among the PGMs#
Osmium is the densest of the eight metals in this comparison, denser than iridium, its closest rival, by 0.025 g/cm3. The ranking below covers all six platinum group metals plus gold and silver, the two comparison metals most often searched alongside them, sourced to Wikipedia's element infoboxes (CRC/Arblaster-derived).
| Rank | Element | Symbol | Density (g/cm3, 20°C) | Group |
|---|---|---|---|---|
| 1 | Osmium | Os | 22.587 | Heavy PGM |
| 2 | Iridium density | Ir | 22.562 | Heavy PGM |
| 3 | Platinum density | Pt | 21.452 | Heavy PGM |
| 4 | Gold | Au | 19.283 | Comparison (border) |
| 5 | Rhodium density | Rh | 12.423 | Light PGM |
| 6 | Ruthenium density | Ru | 12.364 | Light PGM |
| 7 | Palladium density | Pd | 12.007 | Light PGM |
| 8 | Silver | Ag | 10.503 | Comparison (border) |
Tungsten (19.3 g/cm3) is sometimes searched alongside osmium because the two are confused in casual "heaviest metal" lists, but tungsten is not a PGM, gold or silver and does not belong in this ranking; its density simply sits close to gold's, a coincidence, not a comparison this page draws further.
Why Osmium Is So Dense#
Osmium sits in the heavy PGM band (21.5-22.6 g/cm3) together with platinum and iridium, the other two heavy platinum group metals, because lanthanide-shell electron screening and relativistic contraction hold its atomic radius nearly level with the lighter row of metals above it despite carrying far more mass. Osmium's empirical atomic radius is 135 picometers against ruthenium's 134 picometers, essentially identical, even though osmium carries about 88% more atomic mass. Two effects combine to produce that mismatch: the 4f electron shell that fills across the lanthanide series screens the nuclear charge poorly, pulling in the outer orbitals of every element from hafnium onward, and at osmium's high atomic number the innermost electrons move fast enough for relativistic mass increase to contract the s and p orbitals further, which in turn lets the d orbitals expand only slightly. The combined result is an atom barely larger than its lighter 4d-row counterpart, packed with nearly double the mass, which is why osmium and its heavy-PGM neighbors are roughly twice as dense as ruthenium, rhodium and palladium directly above them despite similar atomic sizes.
Is Osmium the Densest Element?#
Osmium is the densest element at ambient pressure, leading iridium by a narrow, well-established margin. Osmium's 22.587 g/cm3 (the Wikipedia figure; J.W. Arblaster's own 2013 paper in Platinum Metals Review gives 22.589 g/cm3 for the same crystallographic lineage) sits 0.025-0.027 g/cm3 above iridium's 22.562 g/cm3, a gap settled only in the 1990s once X-ray crystallography became precise enough to separate the two reliably. The two figures are never both attributed to Johnson Matthey: 22.587 is Wikipedia's, 22.589 is Arblaster's, and a writer should pick one lineage and say so rather than mixing them. Osmium holds the lead at every temperature above roughly 150 K, and iridium only overtakes it under pressure, above 2.98 GPa at room temperature, where both metals reach an identical 22.750 g/cm3 (Arblaster, Johnson Matthey Technology Review, 2014). See osmium vs iridium density for the full margin and its history.
Legacy vs Modern Osmium Density Figures#
Osmium's current, modern figure is the 22.587 g/cm3 crystallographic value; an older Johnson Matthey handbook figure of 22.61 g/cm3 still circulates in comparison tables reproduced from Johnson Matthey and Goodfellow data. The gap traces to method, not to a changed fact: legacy figures came from pycnometric, bulk-sample measurement, which under-reads any metal with residual porosity, microvoids or inclusions, and osmium, a brittle, hexagonal close-packed metal with a conventional handbook melting point near 3,033°C, is unusually hard to consolidate to its full theoretical density. Modern crystallographic densities are calculated directly from unit-cell dimensions and atomic weight and are blind to those defects, which is why the crystallographic figure, not the older bulk one, is the value this page and its ranking table use throughout.
Osmium's Density and Its Reactive Surface#
Solid osmium metal is chemically stable and not dissolved by aqua regia, but its surface slowly oxidizes in ordinary air to volatile osmium tetroxide, a separate fact from its density. Fine osmium powder reacts with atmospheric oxygen at room temperature to form osmium tetroxide (OsO4) over time, though bulk synthesis of the compound requires heating to 400°C; osmium is, in that sense, the least air-stable of the platinum group metals in finely divided form even though the solid metal itself resists acids. Osmium tetroxide is toxic and volatile, which is the real reason osmium is normally sold and handled as an alloy or under an inert atmosphere rather than exposed to air in bulk, not because of the metal's mass per volume.
Osmium Density vs Gold and Silver#
Gram for gram, osmium and gold occupy different volumes because their densities differ: osmium, at 22.587 g/cm3, is about 17.1% denser than gold's 19.283 g/cm3 and roughly 115% denser than silver's 10.503 g/cm3. The same 100 grams of metal packs into a noticeably smaller space as osmium than as either comparison metal.
| Metal | Density (g/cm3) | Volume of 100 g |
|---|---|---|
| Osmium | 22.587 | 4.427 cm3 |
| Gold | 19.283 | 5.186 cm3 |
| Silver | 10.503 | 9.521 cm3 |
Why Osmium's Density Matters#
Osmium's density concentrates unusually large mass into a small volume, which is why osmium-iridium alloys, not the pure metal, historically supplied the hard, wear-resistant tips used in fountain pen nibs, phonograph styli and precision instrument pivots, per Wikipedia's osmium entry. The same property means a buyer of crystalline osmium as an investment receives a strikingly compact, heavy piece for a given mass, since 100 g of osmium occupies barely more room than a large sugar cube, 4.427 cm3 by the table above.
Other Osmium Properties#
Osmium's other physical and chemical properties are covered on their own pages:
- Osmium Properties: the full set of physical and chemical data
- Osmium Melting Point and Boiling Point: thermal behavior at the extreme end of the PGMs
- Osmium Toxicity and Health Effects: the OsO4 hazard profile in detail
Osmium Density and Price#
Density is fixed; osmium's price moves daily and is tracked separately. Current levels and bid/ask context live on the osmium price today page, part of the site's wider platinum group metal prices coverage, with day-by-day movement on the osmium price chart.
Frequently Asked Questions#
How heavy would a 1 inch cube of osmium be? A 1 inch (2.54 cm) cube has a volume of 16.387 cm3, so at 22.587 g/cm3 it weighs about 370 g (13.06 oz), barely more than the 369.7 g an identical iridium cube would weigh.
Is anything denser than osmium? No element is denser than osmium at ordinary pressure. Iridium is the closest rival at 22.562 g/cm3, just 0.11% below osmium, and only overtakes it above 2.98 GPa, a laboratory pressure well outside ordinary use.
What is the cost of 1 g of osmium? Density and cost are unrelated. Osmium's price reflects rarity, refining supply and trading volume, not mass per volume, and current per-gram levels are tracked on the osmium price page above.
Why is osmium so cheap? Osmium's price does not track its density. Levels vary widely between powder and crystalline forms and depend on rarity and thin trading volume; see the osmium price page above rather than assuming one "cheap" figure.
How much is 1 pound of osmium worth? Weight and worth are separate here. A pound (453.6 g) of osmium occupies only about 20.1 cm3, a cube roughly 2.7 cm on each side, because of its density; market worth is tracked on the osmium price page, not fixed by that volume.
Why can't I lick osmium? Not because of its density. Its surface slowly oxidizes in air to volatile, toxic osmium tetroxide, which is why the metal is normally kept as an alloy or sealed away from air rather than handled bare.