How dense is Earth? On average, the planet has a density of about 5.51 g/cm3 (5,513 kg/m3, or about 344 lb/ft3). That is roughly 5.5 times the density of water. NASA gets this figure by dividing Earth’s mass, 5.9722 x 10^24 kg, by its volume, about 1.0832 x 10^21 cubic meters.
How Dense Is Earth in Other Units? Convert It
Science books usually give the figure in grams per cubic centimeter. Engineers, however, prefer kilograms per cubic meter, and US readers may think in pounds per cubic foot. So type any value below, for example 5.513 for the planet or 13.09 for the center, and the converter does the math.
First of all, density is simply mass divided by volume. For a planet, though, you cannot drop it on a scale or into a measuring cup. Instead, scientists weigh Earth through gravity and also measure its size from orbit. After that, they divide one number by the other.
The result, about 5.51 g/cm3, makes Earth the densest planet in the solar system. NASA’s Earth fact sheet lists a mean density of 5,513 kg/m3, a mass of 5.9722 x 10^24 kg and a mean radius of 6,371 km. In addition, NASA’s comparison table rounds the same value to 5,514 kg/m3, so you will see both numbers online.
Meanwhile, the rocks you can pick up at the surface weigh in at only about 2.7 g/cm3. In other words, the average is roughly double the density of the crust. As a result, that gap is the clue that a heavy iron core sits deep inside.
How Dense Is Earth? The Figure in Every Unit
To begin with, all values below start from the NASA mean of 5,513 kg/m3. Also, the US units use the exact pound (453.59237 g) and the exact US gallon (3.785411784 L).
| Unit | Earth’s mean density | Plain-English meaning |
|---|---|---|
| g/cm3 | 5.513 | One sugar-cube-sized piece of “average Earth” weighs 5.5 g |
| g/mL | 5.513 | Also the same number, because 1 mL = 1 cm3 |
| kg/L | 5.513 | A 1-liter block weighs about 12.2 lb |
| kg/m3 | 5,513 | A 1-meter cube weighs about 5.5 metric tons |
| lb/ft3 | 344.2 | A 1-foot cube weighs about 344 lb |
| lb/in3 | 0.199 | A 1-inch cube weighs about 3.2 oz (90 g) |
| lb/gal (US) | 46.0 | A gallon-sized lump weighs about 46 lb |
| Specific gravity | 5.51 | In other words, no unit; it means 5.51 times as dense as water |
Printable tip: this table fits on one page, so it works well as a homework or classroom reference. For the water baseline behind the specific gravity row, see how dense water is at different temperatures.
Recommended Tools for Measuring Density at Home
Of course, you cannot measure a planet in the kitchen. However, you can measure the rocks it is made of, and that makes the big number feel real. First, a pocket scale that reads to 0.01 g weighs small samples. Next, a glass graduated cylinder gives you volume by water displacement. Finally, a labeled rock and mineral set lets students compare light crust rocks with heavier, iron-rich ones.
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How Dense Is Earth Layer by Layer?
However, the single average hides a wide range. For instance, near the surface, rock is light. Toward the center, however, iron squeezed by enormous pressure reaches more than twice the planet’s average. Specifically, the figures come from the Preliminary Reference Earth Model (PREM), the standard 1981 model built from earthquake data.
| Layer | Depth (km) | Depth (miles) | Density (g/cm3) | Density (lb/ft3) |
|---|---|---|---|---|
| Continental crust | 0 to about 35 | 0 to about 22 | about 2.7 | about 169 |
| Oceanic crust | 0 to about 7 | 0 to about 4 | about 2.9 | about 181 |
| Mantle | to 2,891 | to 1,796 | 3.38 to 5.57 | 211 to 348 |
| Outer core (liquid) | 2,891 to 5,150 | 1,796 to 3,200 | 9.90 to 12.17 | 618 to 760 |
| Inner core (solid) | 5,150 to 6,371 | 3,200 to 3,959 | 12.76 to 13.09 | 797 to 817 |
So the core is the reason for the high average. For example, it fills only about 16 percent of the planet’s volume, yet it holds roughly a third of its mass. Our guide to mantle density by depth covers the middle layer in detail.
How Dense Is Earth Compared With Other Planets?
Overall, rocky planets cluster between about 3.9 and 5.5 g/cm3. Gas giants, by contrast, are mostly hydrogen and helium, so they sit far lower. Again, the values below come from NASA’s planetary fact sheet.
| Body | Density (kg/m3) | g/cm3 | Compared with Earth |
|---|---|---|---|
| Earth | 5,514 | 5.51 | Densest planet |
| Mercury | 5,429 | 5.43 | Very close, because of a huge iron core |
| Venus | 5,243 | 5.24 | About 5 percent lower |
| Mars | 3,934 | 3.93 | About 29 percent lower |
| Moon | 3,340 | 3.34 | Mostly rock, since its core is small |
| Neptune | 1,638 | 1.64 | Densest giant planet |
| Jupiter | 1,326 | 1.33 | Mostly hydrogen and helium |
| Uranus | 1,270 | 1.27 | Ice giant |
| Saturn | 687 | 0.69 | Therefore less dense than water |
Mercury is the interesting case, because its core takes up far more of the planet than ours does. Even so, Earth’s greater size squeezes its interior harder, and that compression pushes its average density just above Mercury’s.
Earth Density Numbers People Mix Up
In practice, several different figures float around online. Because they all look like “Earth’s density”, students often swap them. So this table separates them.
| Figure | Value | What it actually describes |
|---|---|---|
| Mean density | 5.51 g/cm3 | Total mass divided by total volume |
| Surface rock | about 2.7 g/cm3 | Only granite-type continental crust, so not the whole planet |
| Mantle average | about 4.5 g/cm3 | The rock layer between crust and core |
| Center of Earth | about 13.1 g/cm3 | The single highest value, at 6,371 km depth |
| Specific gravity | 5.51 | Instead, a ratio to water with no units |
| kg/m3 vs g/cm3 | 5,513 vs 5.513 | Same density; in short, multiply g/cm3 by 1,000 |
How Dense Is Earth? Work It Out Step by Step
In fact, you can check the answer yourself with a calculator and three published constants. Here is the method, step by step:
- Start with Earth’s gravity constant. First, satellite tracking gives GM, the product of the gravitational constant and Earth’s mass, as 3.986004418 x 10^14 m3/s2.
- Divide by the gravitational constant. Then, with G = 6.67430 x 10^-11 m3/(kg s2), the mass comes out at about 5.9722 x 10^24 kg.
- Find the volume. Use the mean radius of 6,371 km (6,371,000 m) in V = 4/3 x pi x r3. As a result, you get about 1.0832 x 10^21 m3.
- Divide mass by volume. Next, 5.9722 x 10^24 kg divided by 1.0832 x 10^21 m3 equals about 5,513 kg/m3.
- Convert the units. Finally, divide by 1,000 for g/cm3 (5.513), or enter the result in the converter above for lb/ft3.
In addition, there is a shortcut through surface gravity. Because g = 4/3 x pi x G x density x radius, you can rearrange it as density = 3g / (4 x pi x G x R). Similarly, with NASA’s g of 9.820 m/s2, that formula again gives about 5,513 kg/m3.
How Cavendish Found How Dense Earth Is
In 1798, Henry Cavendish built a torsion balance in a sealed room. Inside, it held two small lead spheres on a six-foot rod hanging from a wire. Next, he moved two 350-pound lead balls close to them and watched the rod twist by a tiny amount through a telescope.
In turn, that twist let him compare the pull between the lead balls with Earth’s own pull. According to the American Physical Society’s history of the experiment, he found Earth to be 5.48 times as dense as water. Even so, that result sits within about 1 percent of today’s 5.51, which is remarkable for a wooden rod and a candle-lit room.
Lead was a smart choice, too. Because it is about twice as dense as average Earth, it packs a lot of mass into a small ball. For the numbers behind that metal, see how dense lead is compared with other metals.
Do and Don’t When Quoting Earth’s Density
Do
- Say “mean” or “average” when you quote 5.51 g/cm3.
- Name your source as well, for example NASA or PREM.
- Also keep units with the number every time.
- Round to two or three significant figures, since that suits school work.
- Finally, separate layer values from the whole-planet value.
Don’t
- Call 5.51 g/cm3 the density of the crust or core.
- Mix kg/m3 and g/cm3 in one calculation, because the answer will be off by 1,000.
- Assume the core is twice as dense everywhere; it ranges from 9.9 to 13.1.
- Quote 5.48 as the modern value; that was Cavendish’s 1798 result.
- Treat the round 5.5 as exact, since it is only an approximation.
Honest Limits of These Numbers
On the whole, the mean density is very well known, because both mass and size are measured precisely. For example, NASA’s 5,513 and 5,514 kg/m3 differ only because of rounding. The layer values, however, carry more uncertainty. After all, seismic waves reveal stiffness and density together, so the deep figures could be off by a few percent.
Also, PREM gives one value per depth for the whole planet. In reality, Earth is lumpier: cold sinking slabs, hot plumes and thick continental roots all shift local density slightly. Finally, Earth is not a perfect sphere. Instead, it bulges at the equator (6,378 km) and flattens at the poles (6,357 km), so the 6,371 km figure is the radius of a sphere with the same volume.
When Accuracy Really Matters
For a quiz or a school report, therefore, “about 5.5 g/cm3” is a solid answer. Still, a few uses call for more care:
- Physics homework. Carry four significant figures (5.513) through the math, and round only at the end.
- Science fair projects. If you measure rock samples, then report the scale resolution and how you read the cylinder.
- Research or engineering. In that case, use the latest published constants and cite the exact model or data set.
Frequently Asked Questions
How dense is Earth in g/cm3?
Earth’s mean density is about 5.51 g/cm3. In other words, NASA lists it as 5,513 kg/m3, which equals 5.513 g/cm3.
How dense is Earth in kg/m3?
About 5,513 kg/m3, according to the NASA Earth fact sheet. The NASA planet comparison table rounds it to 5,514 kg/m3.
How dense is Earth in pounds per cubic foot?
About 344 lb/ft3. For example, a cube of average Earth material 1 foot on each side would weigh about 344 pounds.
Is Earth the densest planet?
Yes. At about 5.51 g/cm3, Earth is the densest planet in the solar system. Meanwhile, Mercury comes second at about 5.43 g/cm3.
Why is Earth denser than its surface rocks?
Surface rocks average about 2.7 g/cm3, but the iron-nickel core is about 9.9 to 13.1 g/cm3. As a result, the heavy core and the compressed lower layers pull the average up to 5.51.
What is the densest part of Earth?
The inner core. In particular, at the very center, the PREM model gives about 13.09 g/cm3, or roughly 817 lb/ft3.
How dense is Earth compared with water?
Roughly speaking, about 5.5 times as dense. In short, that ratio, 5.51, is Earth’s specific gravity.
Who first measured how dense Earth is?
Henry Cavendish, in 1798, used a torsion balance with lead spheres and found Earth to be 5.48 times as dense as water.
How do scientists know Earth’s mass?
Satellite orbits give GM, the gravitational constant times Earth’s mass. Then, dividing by the measured value of G gives about 5.9722 x 10^24 kg.
Does Earth’s density change over time?
Not in any way you could measure day to day. Meteorite dust adds a little mass and gas escapes from the atmosphere, but both are tiny compared with the planet’s total.
The Bottom Line
To sum up, Earth’s mean density is about 5.51 g/cm3, or 5,513 kg/m3 and 344 lb/ft3. That is mass divided by volume for the whole planet. By contrast, the crust is only about half that, while the iron core reaches roughly 13 g/cm3 at the center.
So when you quote the number, first say which one you mean, keep the units attached, and use the converter at the top of the page for any other unit.
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