How dense is uranium? Uranium metal has a density of about 19.1 g/cm3 (19,100 kg/m3), or roughly 0.69 pounds per cubic inch and 1,190 pounds per cubic foot. That makes it about 1.7 times as dense as lead and just below gold and tungsten. Uranium dioxide reactor fuel, by contrast, is only about 10.96 g/cm3.
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How Dense Is Uranium in Other Units?
First, the converter starts at 19.1 g/cm3, the standard handbook value for uranium metal. Then, when you change the number or the unit, it gives kilograms per cubic meter, grams per milliliter, pounds per cubic inch, pounds per cubic foot and pounds per US gallon.
To begin with, uranium is element 92, a silvery, mildly radioactive metal. Martin Klaproth first identified it in 1789, and later Eugene Peligot first made the pure metal in 1841. Today, most people therefore know it as reactor fuel. However, its density is a story of its own, and it explains several of its everyday industrial uses.
For a trusted figure, the Royal Society of Chemistry lists uranium at 19.1 g/cm3 on its uranium element page. In addition, careful lab measurements of pure alpha uranium give a slightly more precise 19.05 g/cm3 near room temperature. As a result, you will see both numbers, and both are correct to the precision they claim.
To make that figure easier to picture, a 1-inch cube of uranium would weigh about 313 grams, or 11.0 ounces. In other words, a cube about the size of a large die would weigh almost as much as a full can of soup.
How Dense Is Uranium Compared With Lead, Gold and Tungsten?
First, the table ranks uranium against the heavy metals people usually compare it with. Also, all values are for the pure metal near room temperature. In addition, the last column shows how many times denser uranium is, or how far it falls short.
| Material | g/cm3 | lb/ft3 | lb/in3 | Uranium vs this |
|---|---|---|---|---|
| Osmium | 22.59 | 1,410 | 0.816 | uranium about 15% lighter |
| Platinum | 21.45 | 1,339 | 0.775 | uranium about 11% lighter |
| Gold | 19.32 | 1,206 | 0.698 | uranium about 1% lighter |
| Tungsten | 19.25 | 1,202 | 0.695 | uranium about 1% lighter |
| Uranium metal | 19.1 | 1,192 | 0.690 | – |
| Mercury (liquid) | 13.53 | 845 | 0.489 | 1.4 times denser |
| Lead | 11.34 | 708 | 0.410 | 1.7 times denser |
| Uranium dioxide (UO2) | 10.96 | 684 | 0.396 | 1.7 times denser |
| Steel | 7.85 | 490 | 0.284 | 2.4 times denser |
| Aluminum | 2.70 | 169 | 0.098 | 7.1 times denser |
| Water | 1.00 | 62.4 | 0.036 | 19.1 times denser |
So uranium is not the densest metal, even though many people assume it is. In fact, gold and tungsten edge past it by about 1 percent, and osmium wins outright. For example, for the full story on the record holder, see how dense osmium is. Meanwhile, tungsten sits almost level with uranium, and our tungsten density guide explains why it often replaces uranium where a heavy, non-radioactive metal is needed.
On the other hand, lead is the more useful everyday comparison. Because uranium is 1.68 times denser, a uranium part takes up only about 59 percent of the space of a lead part with the same weight. Similarly, our page on lead density shows the same math for lead itself.
How Dense Is Uranium When It Is Depleted or Enriched?
To start, natural uranium is a mix of isotopes: about 99.27 percent uranium-238, 0.72 percent uranium-235 and a trace of uranium-234. Depleted uranium (DU), by contrast, is what is left over after enrichment. Specifically, the US Nuclear Regulatory Commission defines depleted uranium as uranium with less uranium-235 than the 0.7 percent found in nature. In practice, it usually holds about 0.2 to 0.3 percent.
So does that change the density? Hardly. After all, uranium-235 atoms are only about 1 percent lighter than uranium-238 atoms, and they make up less than 1 percent of the metal. As a result, DU works out to about 19.05 g/cm3, the same as natural uranium to three significant figures. Instead, the differences that matter are alloying, temperature and porosity.
| People often confuse | What it is | Typical density |
|---|---|---|
| Natural uranium metal | About 0.72% U-235, pure metal | 19.1 g/cm3 (19.05 precise) |
| Depleted uranium metal | Below 0.7% U-235, usually 0.2-0.3% | about 19.05 g/cm3 |
| Uranium dioxide (UO2) | Ceramic oxide used as reactor fuel | 10.96 g/cm3 theoretical |
| Uranium ore | Rock containing a small share of uranium minerals | similar to ordinary rock |
| Atomic weight | Mass of one atom, not a density | 238.03 (no volume unit) |
How Dense Is Uranium Dioxide Fuel?
However, most power reactors do not burn uranium metal. Instead, they use small ceramic pellets of uranium dioxide, UO2. Its theoretical density, calculated from its crystal structure, is about 10.96 g/cm3, and many references round it to 10.97. In other words, that is a little lower than lead.
Yet real pellets never reach the full theoretical figure, because sintering leaves tiny pores. Manufacturers therefore usually quote density as a percentage of theoretical density, often about 95 percent or higher. For example, at 95 percent, a pellet comes out near 10.4 g/cm3.
Why is the oxide so much less dense than the metal? First, oxygen atoms take up space while adding little mass. Second, the oxide crystal is more open than the metal. As a result, uranium makes up only about 88 percent of UO2 by mass, so each cubic centimeter of fuel holds about 9.66 grams of uranium. By comparison, the metal holds 19.1 grams, roughly twice as much.
How Dense Is Uranium in Real Life? Weight by Size
Next, density turns into weight once you know the volume. So here is what uranium metal would weigh in sizes that are easy to picture. Also, each row uses 19.1 g/cm3 and exact US unit definitions.
| Amount | Volume | Metric weight | US weight |
|---|---|---|---|
| 1 cm cube | 1 cm3 | 19.1 g | 0.67 oz |
| 1-inch cube | 16.39 cm3 | 313 g | 11.0 oz |
| 2-inch cube | 131.1 cm3 | 2.50 kg | 5.52 lb |
| 1 liter | 1,000 cm3 | 19.1 kg | 42.1 lb |
| 1 US gallon | 3,785 cm3 | 72.3 kg | 159.4 lb |
| 1 cubic foot | 28,317 cm3 | 541 kg | 1,192 lb |
| 1 kilogram of uranium | 52.4 cm3 (3.19 in3) | 1 kg | 2.20 lb |
In short, a gallon jug of uranium would weigh more than most adults. Meanwhile, a cubic foot would weigh more than half a metric ton.
Recommended Tools for Measuring Metal Density
Of course, you will never need to test uranium at home, and you should not try. Still, the same two tools check the density of any safe metal object, from a ring to a fishing sinker. First, choose a scale that reads to 0.01 g. Next, add a narrow glass graduated cylinder, so a small object makes a readable change in water level.
How to Measure the Density of a Metal Sample
First of all, this water displacement method works for any ordinary metal object. However, do not use it on radioactive or toxic materials.
- Weigh the dry object. First, place it on a 0.01 g scale and note the mass in grams.
- Fill a graduated cylinder partway. Next, add enough water to cover the object, then read the level at eye height.
- Lower the object in gently. Then tilt the cylinder and slide the object down so no water splashes out.
- Read the new water level. As a result, the rise in milliliters equals the object’s volume in cubic centimeters.
- Divide mass by volume. For example, 50 g divided by 4.4 mL gives about 11.4 g/cm3, close to lead.
- Convert the result. Finally, enter it in the converter above to see lb/in3 or lb/ft3.
Why Is Uranium So Dense?
In general, density depends on two things: how heavy each atom is and how closely the atoms sit together. Uranium, in particular, scores very high on the first and reasonably well on the second.
- Very heavy atoms. With an atomic weight of about 238, uranium has the heaviest atoms of any element found in quantity in nature.
- A compact metal lattice. In addition, at room temperature, uranium forms an orthorhombic crystal called alpha uranium, which packs its atoms fairly tightly.
- Less tight than gold. However, gold and tungsten fit their atoms closer together, so they finish slightly ahead despite lighter atoms.
Because the atoms are so heavy, roughly 4.8 x 10^22 of them fill a cubic centimeter and weigh about 19 grams. By comparison, that same cube of water weighs just 1 gram.
Where Uranium’s Density Matters in Industry
Apart from fuel, uranium’s density is the reason depleted uranium found industrial work. For example, the Royal Society of Chemistry lists ship ballast and aircraft counterweights among its uses. In addition, dense DU has served as shielding in containers that carry radioactive sources and in some industrial radiography equipment, because dense metals block gamma rays well.
That said, many of these jobs have moved to tungsten. After all, tungsten is almost as dense, it is not radioactive, and it needs no special licensing. That is also why our tungsten guide pairs so closely with this one.
Do and Don’t When Comparing Dense Metals
Do
- State the temperature and purity behind a density figure.
- Also keep metal density and oxide density separate.
- Use g/cm3 or kg/m3 so that you compare sources fairly.
- Treat 19.1 and 19.05 g/cm3 as the same value at different precision.
Don’t
- Confuse atomic weight with density.
- Call uranium the densest element; osmium holds that title.
- Apply the metal figure to fuel pellets, because they are oxide.
- Handle uranium or test it yourself, since it is regulated.
Honest Limits of These Numbers
To begin with, every density on this page is a rounded reference value, not a measurement of a particular part. For one thing, temperature matters, because metals expand as they warm and lose a little density. Alloys also matter, since even small additions such as titanium or molybdenum change the figure slightly. Similarly, cast parts can hold tiny voids, while fuel pellets are deliberately left a few percent porous. In short, use 19.1 g/cm3 for estimates and an engineering data sheet for anything critical.
Frequently Asked Questions
How dense is uranium in g/cm3?
Uranium metal is about 19.1 g/cm3, although it is often given more precisely as 19.05 g/cm3 near room temperature.
How dense is uranium in pounds per cubic inch?
In US units, uranium is about 0.69 pounds per cubic inch, or about 1,192 pounds per cubic foot.
Is uranium denser than lead?
Yes. In fact, uranium at 19.1 g/cm3 is about 1.7 times as dense as lead at 11.34 g/cm3.
Is uranium denser than gold?
No. Gold, at 19.32 g/cm3, is about 1 percent denser than uranium, even though uranium atoms are heavier.
Is uranium the densest element?
No. Instead, osmium is the densest element at about 22.59 g/cm3, followed by iridium. In addition, platinum, gold and tungsten are denser than uranium.
How dense is uranium that has been depleted?
Depleted uranium is about 19.05 g/cm3, essentially the same as natural uranium, because removing some uranium-235 barely changes the average atomic mass.
What is the density of uranium dioxide fuel?
Uranium dioxide has a theoretical density of about 10.96 g/cm3. However, sintered fuel pellets usually reach only about 95 percent of that.
How much does a cubic inch of uranium weigh?
For example, a 1-inch cube of uranium metal weighs about 313 grams, or about 11 ounces.
How dense is uranium compared with tungsten?
The two are very close. In fact, tungsten is about 19.25 g/cm3, so it is roughly 1 percent denser than uranium.
Why is uranium so heavy?
First, each uranium atom has an atomic weight of about 238, the highest of any element common in nature, and the metal packs those atoms closely.
The Bottom Line
To sum up, uranium metal weighs in at about 19.1 g/cm3, or 0.69 lb/in3. As a result, it is 1.7 times denser than lead, but slightly below gold and tungsten and well below osmium. Likewise, depleted uranium has essentially the same density, while uranium dioxide fuel is much lighter at about 10.96 g/cm3.
Finally, if you need the figure in another unit, the converter at the top handles any density. Instead, for hands-on practice, measure a safe metal object with a scale and a graduated cylinder instead.
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