How dense is osmium? Osmium has a density of about 22.59 g/cm3 (22,587 kg/m3) at room temperature, or roughly 0.816 pounds per cubic inch and 1,410 pounds per cubic foot. That makes it the densest naturally occurring element, just ahead of iridium at 22.56 g/cm3 and about twice as dense as lead.
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How Dense Is Osmium in Other Units?
The converter starts at 22.587 g/cm3, the X-ray value for pure osmium. Then, if you change the number or the unit, it returns kilograms per cubic meter, grams per milliliter, pounds per cubic inch, pounds per cubic foot and pounds per US gallon.
First of all, osmium is element 76, a hard, brittle, bluish-white metal in the platinum group. Smithson Tennant first found it in 1803 while dissolving crude platinum, and he named it after the Greek word “osme”, meaning smell, because its oxide has a sharp, chlorine-like odor. Still, few people ever hold a piece. In fact, world production is only a few hundred kilograms to a few tonnes a year.
Even so, its density is famous. The Royal Society of Chemistry lists osmium at 22.5872 g/cm3 on its osmium element page, and it calls the metal the densest of all elements. It also notes that the title has gone back and forth with iridium, as you will see below.
For example, to put the number in your hand, a 1-inch cube of osmium would weigh about 370 grams, or 13.1 ounces. In other words, that is more than a full can of soda, squeezed into a cube smaller than a golf ball.
How Dense Is Osmium Compared With Gold, Platinum and Lead?
First, the table ranks osmium against the heavy metals people usually ask about. All values are for the pure metal near room temperature, so alloys and coins will differ slightly. In addition, the last column shows how much denser osmium is than each one.
| Metal | g/cm3 | lb/ft3 | lb/in3 | Osmium is denser by |
|---|---|---|---|---|
| Osmium | 22.59 | 1,410 | 0.816 | – |
| Iridium | 22.56 | 1,408 | 0.815 | about 0.1% |
| Platinum | 21.45 | 1,339 | 0.775 | about 5% |
| Rhenium | 21.02 | 1,312 | 0.759 | about 7% |
| Gold | 19.32 | 1,206 | 0.698 | about 17% |
| Tungsten | 19.25 | 1,202 | 0.695 | about 17% |
| Uranium | 19.05 | 1,189 | 0.688 | about 19% |
| Mercury (liquid) | 13.53 | 845 | 0.489 | about 67% |
| Lead | 11.34 | 708 | 0.410 | about 2 times |
| Iron | 7.87 | 492 | 0.284 | about 2.9 times |
| Aluminum | 2.70 | 169 | 0.098 | about 8.4 times |
| Water | 1.00 | 62.3 | 0.036 | about 22.6 times |
So gold, which most people think of as the heavy metal, is about 17 percent lighter than osmium for the same size. Similarly, platinum falls about 5 percent short. For the full picture on those two, also see how dense platinum is and the density of gold. Meanwhile, tungsten, at 19.25 g/cm3, is the dense metal you are far more likely to own, and our tungsten density guide explains why it stands in for gold in fakes.
Osmium vs Iridium: Which Is the Densest Element?
For most of the 20th century, however, chemistry books disagreed. For instance, some named osmium, while others named iridium. This happened because the two are extremely close, and early measurements of real samples were thrown off by tiny pores, impurities and the difficulty of working such hard metals.
Eventually, the question was settled by calculation rather than by weighing. Because a crystal’s density follows from its atomic mass and the spacing of its atoms, X-ray measurements of that spacing give a cleaner answer than a lump of metal ever can. Then, in 1989, J. W. Arblaster reviewed the latest crystal data in Platinum Metals Review and arrived at 22.587 g/cm3 for osmium and 22.562 g/cm3 for iridium at 20 C (68 F).
| Property | Osmium (Os) | Iridium (Ir) |
|---|---|---|
| Atomic number | 76 | 77 |
| Atomic weight | 190.23 | 192.22 |
| Crystal structure | Hexagonal close-packed | Face-centered cubic |
| X-ray density at 20 C | 22.587 g/cm3 | 22.562 g/cm3 |
| Weight of a 1-inch cube | 370.1 g (13.06 oz) | 369.7 g (13.04 oz) |
| Melting point | 3,033 C (5,491 F) | 2,446 C (4,435 F) |
In fact, the gap is only 0.025 g/cm3, or about 0.11 percent. On a 1-inch cube, for example, that is roughly 0.4 grams, which is less than the weight of a paper clip. As a result, the Royal Society of Chemistry jokes that the two are joint winners. Still, by the best crystal data, osmium keeps the title.
How Dense Is Osmium in Real Life? Weight by Size
Next, density turns into weight once you know the volume. So here is what pure osmium would weigh in shapes and amounts that are easy to picture. Also, each row uses 22.587 g/cm3 and exact US unit definitions.
| Amount of osmium | Volume | Metric weight | US weight |
|---|---|---|---|
| 1 cm cube | 1 cm3 | 22.59 g | 0.80 oz |
| 1-inch cube | 16.39 cm3 | 370.1 g | 13.06 oz |
| 2-inch cube | 131.1 cm3 | 2.96 kg | 6.53 lb |
| Golf-ball-sized sphere (42.7 mm) | 40.7 cm3 | 919 g | 2.03 lb |
| 1 liter (10 cm cube) | 1,000 cm3 | 22.59 kg | 49.80 lb |
| 1 US gallon | 3,785 cm3 | 85.50 kg | 188.5 lb |
| 1 cubic foot | 28,317 cm3 | 639.6 kg | 1,410 lb |
| 1 kilogram of osmium | 44.27 cm3 (2.70 in3) | 1 kg | 2.20 lb |
In other words, a single cubic foot of osmium would weigh about as much as a small car. Similarly, the converter above handles any density, and our guide to lead density shows the same math for a metal half as heavy.
Recommended Tools for Measuring Metal Density
Admittedly, you will probably never test osmium at home. However, the same two tools check the density of any metal piece, from a ring to a fishing weight: a precise scale and a graduated cylinder. First, choose a scale that reads to 0.01 g. Next, add a narrow glass cylinder, because a small object raises the water level only a little.
Why Is Osmium So Dense?
In general, density depends on two things: how heavy each atom is and how closely the atoms sit together. Osmium, in particular, does well on both counts.
- Heavy atoms. Each osmium atom has an atomic weight of about 190, so it carries roughly 190 times the mass of a hydrogen atom.
- Small atoms. Specifically, across the lanthanide series, the nucleus pulls the electrons in more tightly, which is called the lanthanide contraction. In addition, relativistic effects on the inner electrons add to it. Therefore, osmium atoms are barely larger than the much lighter atoms above them in the periodic table.
- Tight packing. Finally, osmium crystallizes in a hexagonal close-packed structure, which fills about 74 percent of the space, the most any arrangement of equal spheres can manage.
As a result, about 7.15 x 10^22 osmium atoms fit in one cubic centimeter. Because each one is so heavy, that cube weighs more than 22 grams. Meanwhile, the same cube of water weighs just 1 gram.
Densest, Heaviest and Hardest Are Not the Same
People often swap these words. However, they describe different things, so the table separates them.
| Term | What it means | Top element |
|---|---|---|
| Densest | Most mass in a given volume (g/cm3) | Osmium, then iridium |
| Heaviest atom | Highest atomic weight per atom | Synthetic elements such as oganesson; uranium among common natural ones |
| Hardest metal | Resists scratching and denting | Chromium is often cited; osmium is also very hard (about 7 on the Mohs scale) but brittle |
| Weight | The force of gravity on a whole object | Depends on size, not just material |
So a uranium atom is heavier than an osmium atom, yet uranium metal is less dense, because its atoms are spaced farther apart. Likewise, a large block of lead outweighs a tiny osmium bead, even though osmium is the denser material.
How to Measure the Density of a Metal Sample
In general, this water displacement method works for any solid metal object that does not react with water. In fact, it is the same idea scientists used before X-ray methods took over.
- Weigh the dry sample. First, place it on a scale that reads to 0.01 g and record the mass in grams.
- Half-fill a graduated cylinder. Then add enough water to cover the sample completely, and read the level at the bottom of the curved surface.
- Lower the sample in gently. Next, tilt the cylinder and let the piece slide down so no water splashes out.
- Tap out air bubbles. Because bubbles stuck to the metal add false volume, tap the glass until they rise.
- Read the new water level. After that, subtract the first reading; the difference in mL equals the sample’s volume in cm3.
- Divide mass by volume. Finally, enter the result in the converter above to see it in pounds per cubic inch or other units.
Do
- Quote osmium as 22.59 g/cm3 (22,587 kg/m3).
- Name the temperature when precision matters.
- Also mention iridium when you call osmium the densest.
- Similarly, use mass divided by volume for any density check.
- Remove air bubbles before reading the water level.
Don’t
- Call gold or lead the densest metal.
- Likewise, never confuse density with atomic weight.
- Expect a small sample to match the X-ray value exactly.
- Above all, never heat or powder osmium at home.
- Round iridium up so it ties osmium.
Honest Limits of the Number
The figure 22.587 g/cm3 describes a perfect crystal of pure osmium at 20 C. Real samples, however, fall a little short. For example, pressed or sintered osmium contains tiny pores, and even a fraction of a percent of trapped space can drop the measured value below iridium’s. Temperature matters too, because the metal expands slightly as it warms. In addition, the result rests on the measured lattice spacing and on the average atomic weight of osmium’s isotopes, so different handbooks may list 22.57 to 22.61 g/cm3. In short, any value near 22.6 g/cm3 is right for everyday use.
When Accuracy Really Matters
Overall, for trivia, homework and general comparisons, 22.59 g/cm3 is all you need. Still, a few situations call for more care:
- Osmium vs iridium claims. The two differ by only about 0.1 percent, so a ranking needs X-ray data, not a home measurement.
- Engineering and alloys. Osmium is almost always used in hard alloys for pen tips, instrument pivots and electrical contacts, and an alloy’s density is lower than the pure metal’s. Use the supplier’s data sheet instead.
- Lab chemicals. For example, osmium tetroxide is used to stain samples for electron microscopy and to oxidize chemicals in research labs. So follow the safety data sheet and your institution’s rules.
Frequently Asked Questions
How dense is osmium in g/cm3?
Osmium has a density of about 22.59 g/cm3 at 20 C (68 F). More precisely, the X-ray value is 22.587 g/cm3, which equals 22,587 kg/m3.
How dense is osmium in pounds?
In US units, osmium is about 0.816 pounds per cubic inch, 1,410 pounds per cubic foot and 188.5 pounds per US gallon.
Is osmium really denser than iridium?
Yes, by a tiny margin. Specifically, X-ray data give 22.587 g/cm3 for osmium and 22.562 g/cm3 for iridium, a gap of about 0.11 percent.
How dense is osmium compared with gold?
Osmium is about 17 percent denser than gold, which is 19.32 g/cm3. For example, a 1-inch cube of gold weighs about 317 grams, against about 370 grams for osmium.
How dense is osmium compared with lead?
Osmium is almost exactly twice as dense as lead. Lead is 11.34 g/cm3, so osmium comes out about 1.99 times as dense.
Why is osmium so dense?
First, its atoms are heavy, with an atomic weight of about 190, and small because of the lanthanide contraction. They also pack in a tight hexagonal close-packed crystal.
What is the densest element on Earth?
Osmium is the densest naturally occurring element at about 22.59 g/cm3, with iridium a very close second. After that, platinum comes third among common metals at 21.45 g/cm3.
How much would a cubic foot of osmium weigh?
In total, a cubic foot of pure osmium would weigh about 1,410 pounds, or 640 kilograms.
Is osmium dangerous to touch?
In general, solid osmium metal at room temperature is considered stable. Instead, the danger is osmium tetroxide, a toxic, volatile oxide that forms from fine powder or hot metal.
Is osmium the heaviest element?
No. Osmium is the densest; however, heavier atoms exist, such as uranium and synthetic elements. After all, density compares mass per volume, not the mass of single atoms.
How Dense Is Osmium? The Bottom Line
To sum up, osmium packs about 22.59 g/cm3, or 0.816 lb per cubic inch, which makes it the densest element found in nature. Meanwhile, iridium trails by only 0.025 g/cm3, while platinum, gold and lead fall further behind.
Finally, if you need the number in another unit, use the converter at the top of this page. Also, if you ever meet real osmium, admire its weight but leave the heating and grinding to a lab.
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