The ten densest naturally occurring and synthetic elements ranked by density at standard temperature and pressure — from osmium and iridium to tantalum.
Quick answer: 1. Osmium (Os), 2. Iridium (Ir), 3. Platinum (Pt), 4. Rhenium (Re), 5. Neptunium (Np), 6. Plutonium (Pu), 7. Gold (Au), 8. Tungsten (W), 9. Uranium (U), 10. Tantalum (Ta).
Density is one of the most fundamental properties of the elements, and the top of the list is dominated by platinum-group metals clustered in the lower d-block of the periodic table. All of the densest elements are metals, and the top five all exceed 20 g/cm³ — about twice the density of lead. This ranking uses density at 20 °C and standard atmospheric pressure for each element's most common allotrope. Synthetic elements are included where data exists, but only those with half-lives long enough for reliable measurement at standard conditions.
Osmium is the densest naturally occurring element at 22.59 g/cm³. A member of the platinum group, it is a hard, brittle blue-gray metal used in fountain-pen tips, electrical contacts, and as a catalyst. Its extreme density means a 1-liter block of osmium would weigh about 22.6 kg.
Iridium is the second-densest element at 22.56 g/cm³, just 0.03 g/cm³ shy of osmium. It is the most corrosion-resistant metal known, virtually immune to acid attack, and is used in spark plugs, crucibles, and the standard kilogram prototype.
At 21.45 g/cm³, platinum is the third-densest element and the most familiar of the precious platinum-group metals. It is a malleable, ductile silver-white metal used in catalytic converters, jewelry, lab equipment, and fuel cells.
Rhenium has a density of 21.02 g/cm³. It is one of the rarest elements in Earth's crust but is a critical component in superalloys used in jet-engine turbine blades because it retains strength at extremely high temperatures.
Neptunium is the fifth-densest element at 20.45 g/cm³. It is a synthetic actinide produced in nuclear reactors and is the first transuranium element. Its density is measured in its alpha allotrope at standard conditions.
Plutonium has a density of 19.82 g/cm³ in its alpha allotrope at room temperature. A synthetic actinide best known for nuclear weapons and reactor fuel, it exists in six allotropes at different temperatures, making its physical properties notably complex.
Gold is the seventh-densest element at 19.32 g/cm³. Its extreme density, along with its resistance to tarnish, malleability, and distinctive luster, has made it a standard store of value and a preferred material for jewelry and electronics for thousands of years.
Tungsten has a density of 19.25 g/cm³, nearly identical to gold. It also has the highest melting point of any element (3,422 °C), making it indispensable for incandescent light-bulb filaments, rocket nozzles, and radiation shielding.
Uranium has a density of 18.95 g/cm³. It is the heaviest naturally occurring primordial element and the primary fuel for nuclear power plants. Its density is about 70% higher than lead, which is why depleted uranium is used in armor-piercing projectiles and counterweights.
Rounding out the top ten at 16.69 g/cm³, tantalum is a dense, corrosion-resistant refractory metal used in capacitors, surgical implants, and chemical-processing equipment. Its high density and inertness make it a go-to material for demanding environments.
| # | Name | symbol | atomic_number | group | period | phase_at_room_temp | crystal_structure |
|---|---|---|---|---|---|---|---|
| 1 | Osmium (Os) | Os | 76 | Platinum group (8, 9, 10) | 6 | Solid | Hexagonal close-packed (hcp) |
| 2 | Iridium (Ir) | Ir | 77 | Platinum group | 6 | Solid | Face-centered cubic (fcc) |
| 3 | Platinum (Pt) | Pt | 78 | Platinum group | 6 | Solid | Face-centered cubic (fcc) |
| 4 | Rhenium (Re) | Re | 75 | Transition metal (group 7) | 6 | Solid | Hexagonal close-packed (hcp) |
| 5 | Neptunium (Np) | Np | 93 | Actinide series | 7 | Solid | Orthorhombic |
| 6 | Plutonium (Pu) | Pu | 94 | Actinide series | 7 | Solid | Monoclinic (alpha phase) |
| 7 | Gold (Au) | Au | 79 | Coinage metal (group 11) | 6 | Solid | Face-centered cubic (fcc) |
| 8 | Tungsten (W) | W | 74 | Transition metal (group 6) | 6 | Solid | Body-centered cubic (bcc) |
| 9 | Uranium (U) | U | 92 | Actinide series | 7 | Solid | Orthorhombic |
| 10 | Tantalum (Ta) | Ta | 73 | Transition metal (group 5) | 6 | Solid | Body-centered cubic (bcc) |
Elements are ranked by density at 20 °C and 1 atm (standard temperature and pressure), highest first (rank 1 = densest). Each element uses its most stable allotrope or the form most commonly referenced in standard tables. Values come from the CRC Handbook of Chemistry and Physics (105th Edition) and NIST Standard Reference Database 69: NIST Chemistry WebBook. Where multiple allotropes exist, the densest common allotrope is used (e.g., alpha phase for osmium and iridium). Synthetic elements (neptunium, plutonium) are included with their measured densities at standard conditions. The order is fully reproducible from the density column alone.
Osmium and iridium are adjacent elements (atomic numbers 76 and 77), and their densities are nearly identical — 22.59 vs 22.56 g/cm³. Osmium's slightly higher density comes from its hexagonal close-packed crystal structure, which packs atoms more efficiently than iridium's face-centered cubic arrangement, despite iridium having a slightly higher atomic mass.
Lead (11.34 g/cm³) is often thought of as a heavy metal, but it doesn't crack the top ten. All ten elements on this list are at least 47% denser than lead. The densest common metals many people encounter are actually tungsten (19.25 g/cm³) and gold (19.32 g/cm³).
Under extreme pressure, many elements become denser than osmium at standard conditions. For example, at the pressures found in Earth's core, iron reaches densities of 13 g/cm³ — but that's still less than osmium at standard pressure. Under sufficient compression, most elements surpass osmium's standard-density value, but at 1 atm and 20 °C, osmium remains the densest.