How Much does the Moon Weigh

Short answer

• The Moon does not have one simple weight, because weight depends on gravity, and the Moon is in orbit rather than resting on a scale. The fixed, useful answer is its mass: about 7.35 x 10 to the power of 22 kilograms. That is about 73.5 quintillion metric tons, or about 1.62 x 10 to the power of 23 pounds of mass. It is about 1.23 percent of the mass of Earth, so about 81 Moons would be needed to equal the mass of one Earth. If the question means what a person or an object weighs while standing on the Moon, the answer is personal. Lunar surface gravity is about 1.62 meters per second squared, compared with about 9.80 meters per second squared on Earth. That ratio is about 0.165, so a person or object weighs about 16.5 percent as much on the Moon as on Earth. A person who weighs 150 pounds on Earth would weigh about 24.8 pounds on the Moon, while their mass would stay exactly the same. Divide an Earth weight by 6 for a close estimate, and multiply by 0.165 for a more precise estimate. If the question is taken as a hypothetical measurement of the whole Moon on Earth, the force would be its mass multiplied by Earth gravity: about 7.20 x 10 to the power of 23 newtons. On the surface of the Moon itself, the same mass multiplied by lunar gravity gives about 1.19 x 10 to the power of 23 newtons. Those two numbers describe the same Moon in two different gravitational settings. Neither number should be quoted without saying which gravity was used.

Why the Question Has Two Answers

When a person steps on a bathroom scale on Earth, the scale responds to the pull of Earth gravity on that person’s body. The number is useful because Earth gravity is the setting everyone shares in daily life. The Moon breaks that assumption in two ways. First, the Moon is not standing on a surface in a steady gravitational field in the way a person stands on a floor. Second, the Moon itself creates gravity, so an object resting on the Moon is pulled by the Moon, not by Earth.

That is why scientists prefer mass when they talk about the Moon itself. Mass is the amount of matter in an object. It does not change when the object moves from Earth to the Moon or to deep space. Weight, by contrast, is a force. It is mass multiplied by the local acceleration due to gravity. Change the gravity, and the weight changes, even though nothing has been added to or removed from the object. A reader who wants the size of the Moon as a physical body needs its mass. A reader who wants to know what a trip to the Moon would feel like needs a personal conversion. A reader who wants a dramatic force figure needs to know that the figure only makes sense once a location is chosen. This article gives all three answers, keeps them clearly labeled, and shows the arithmetic behind each one.

The Mass of the Moon in Plain Numbers

The headline figure comes from the NASA National Space Science Data Center Moon Fact Sheet. That fact sheet lists the mass of the Moon as 0.07346 x 10 to the power of 24 kilograms, with Earth listed as 5.9724 x 10 to the power of 24 kilograms and the Moon to Earth ratio listed as 0.0123. Converted to the more familiar form, that is 7.346 x 10 to the power of 22 kilograms. Rounded to three significant figures, that is 7.35 x 10 to the power of 22 kilograms, and that rounded form is used for most statements in this article. The small difference between 7.346 and 7.35 is rounding, not a disagreement about the Moon.

Scientific notation is used because the full number is too long to read comfortably. Written out in full, 7.346 x 10 to the power of 22 kilograms is 73,460,000,000,000,000,000,000 kilograms. In metric tons, where one metric ton equals 1,000 kilograms, the mass is about 73.5 quintillion metric tons. In pounds of mass, using about 2.20462 pounds per kilogram, it is about 1.62 x 10 to the power of 23 pounds. In short tons, it is about 8.10 x 10 to the power of 19 short tons, matching the rounded figure of about 8.1 x 10 to the power of 19 tons given by NASA Glenn Research Center. These are all the same physical quantity in different units, not separate measurements.

The NASA ratio of 0.0123 means the Moon holds about 1.23 percent of the mass of Earth. Taking the reciprocal gives about 81.3, which is why the common shorthand says the Moon is about one eighty-first of Earth by mass. That comparison helps correct a visual impression. The Moon looks large in the sky, and its diameter is more than one quarter of the diameter of Earth, but it is far lighter in proportion to its size than Earth is. The reason is density, covered below.

Mass Is Not Weight

Mass is a property of the object itself. It measures how much matter is present, and it determines how hard it is to speed the object up or slow it down. A 70 kilogram person has a mass of 70 kilograms on Earth, on the Moon, in orbit, and in deep space. Nothing about travel changes that number, apart from eating, drinking, or shedding equipment, which are changes to the body or its load rather than changes caused by location.

Weight is a force. The standard formula is weight equals mass multiplied by gravitational acceleration, written as W equals m times g. Here, m is mass, g is the local acceleration due to gravity, and W is weight as a force. In the International System of Units, mass is measured in kilograms, gravitational acceleration is measured in meters per second squared, and weight is measured in newtons. One newton is the force needed to accelerate a one kilogram mass by one meter per second squared.

On Earth, the confusion is worsened by the word pound. In everyday United States usage, pound is used both for a unit of mass and for a unit of force, and bathroom scales are calibrated to show a convenient number under Earth gravity. A scale does not directly measure mass. It measures a force and then displays a number that matches the mass that would produce that force under Earth gravity. Take the same scale to the Moon, and it would show a smaller number, not because the person lost matter, but because the force is smaller. A balance scale that compares two masses against each other would behave differently, because both sides would be in the same gravity. In short: a spring scale responds to weight, while a comparison of masses responds to mass.

For the Moon itself, the Moon in orbit is in free fall around Earth. It is continuously falling toward Earth while moving forward fast enough to keep missing it, which is what an orbit is in simple terms. An object in free fall does not press on a scale in the way a resting object does. So asking for the weight of the Moon without naming a place is incomplete, in the same way that asking for a price without naming a currency is incomplete. The mass is complete on its own. A weight figure becomes complete only when the gravitational setting is named.

The Hypothetical Weights of the Whole Moon

Even though the Moon cannot be placed on a scale, hypothetical weights are still useful, provided they are labeled as hypothetical. They give a sense of scale, and they show why the choice of gravity matters. The arithmetic uses the same formula, with the mass of the Moon as m and the chosen gravity as g.

For a hypothetical measurement on Earth, using Earth surface gravity of 9.80 meters per second squared, the calculation is 7.346 x 10 to the power of 22 kilograms multiplied by 9.80 meters per second squared, which gives about 7.20 x 10 to the power of 23 newtons. That is the force Earth gravity would exert on the mass of the Moon if that mass could somehow be placed at rest on the surface of Earth. It is a thought experiment, not a practical measurement, and it should never be presented as a number obtained by weighing the Moon.

For a measurement on the surface of the Moon, using lunar surface gravity of 1.62 meters per second squared, the calculation gives about 1.19 x 10 to the power of 23 newtons. This is also a thought experiment. It is about one sixth of the Earth hypothetical figure, because lunar gravity is about one sixth of Earth gravity. The gap between those two figures is the whole point. A single object can be assigned weights that differ by a factor of about six, depending only on where the measurement is imagined to take place.

What You Would Weigh on the Moon

The Moon’s surface gravity, from the NASA fact sheet, is 1.62 meters per second squared. Earth surface gravity in the same fact sheet is 9.80 meters per second squared. Dividing 1.62 by 9.80 gives about 0.165. NASA Glenn Research Center expresses the same relationship as 0.165 Earth gravity. In percentage terms, that is about 16.5 percent. The commonly quoted one sixth is a rounded version of the same ratio, since one divided by six is about 0.167. Both forms are correct as approximations, but 0.165 is closer to the fact sheet values used here.

The conversion method is simple. Take a weight measured on Earth, in pounds, and multiply it by 0.165. For a quick estimate, divide the Earth weight by 6 instead. The divide by 6 method gives a result very close to the more precise method, and it is easy to do without a calculator. The difference is usually less than one pound for ordinary body weights, but the 0.165 method is better when precision matters.

| Earth weight in pounds | Moon weight in pounds, rounded | | 100 | 16.5 | | 120 | 19.8 | | 150 | 24.8 | | 180 | 29.8 | | 200 | 33.1 |

A reader can extend the table with the same rule. A person who weighs 130 pounds on Earth would weigh about 21.5 pounds on the Moon. A person who weighs 160 pounds on Earth would weigh about 26.4 pounds on the Moon. In each case, the mass of the person has not changed. Only the force pulling that mass toward the surface has changed.

The same method works for objects. A backpack with a mass of 10 kilograms weighs about 98 newtons on Earth, using 10 multiplied by 9.80, and about 16.2 newtons on the Moon, using 10 multiplied by 1.62. A small car with a mass of 1,500 kilograms weighs about 14,700 newtons on Earth and about 2,430 newtons on the Moon. The car is no easier to push up to speed in terms of its mass, because accelerating a mass still requires force, but it presses down on the surface with much less force, which is why lifting and carrying feel easier even though inertia does not disappear.

A fuller account of movement in lunar gravity belongs with a general article on gravity on the Moon, noted as an internal link candidate at the end of this article rather than repeated here.

Why Lunar Gravity Is About One Sixth, Not One Eighty-First

If the Moon has only about 1.23 percent of the mass of Earth, why is its surface gravity about 16.5 percent of Earth gravity, rather than about 1.23 percent? Surface gravity depends on two things, not one: the mass of the body, and the distance from its center to its surface, which is its radius. A smaller radius brings a surface object closer to the center of mass, and that closeness partly offsets the smaller total mass.

The NASA fact sheet gives the volumetric mean radius of the Moon as 1,737.4 kilometers, compared with 6,371.0 kilometers for Earth, a ratio of about 0.2727. Surface gravity varies with mass divided by radius squared, so the mass ratio of about 0.0123 divided by the square of the radius ratio, about 0.0744, gives about 0.165, matching the surface gravity ratio in the fact sheet. The one sixth figure and the one eighty-first figure can both be true at the same time because they describe different quantities: one describes surface gravity, the other describes total mass.

Density adds the other half of the explanation. The NASA fact sheet lists the mean density of the Moon as 3,344 kilograms per cubic meter, compared with 5,514 kilograms per cubic meter for Earth, a ratio of about 0.606. The Moon is therefore less dense on average than Earth. Combined with its smaller volume, listed as about 0.0203 times the volume of Earth, the result is a total mass far smaller than a simple diameter comparison would suggest.

NASA Glenn Research Center adds a detail for precision work: the mass of the Moon is not evenly distributed, with mass concentrations, called mascons, beneath many lunar basins. Local surface gravity therefore varies slightly, but the headline figure of 1.62 meters per second squared is an average value suitable for general conversions.

How Scientists Know the Mass Without a Scale

No one has placed the Moon on a scale, and no one needs to. Mass can be found from motion, because gravity links mass to the way objects move. The core idea comes from Newton’s law of universal gravitation, which relates the gravitational force between two bodies to their masses and the distance between them. When a smaller body orbits a larger body, the period of the orbit and the size of the orbit reveal the mass of the larger body, once the gravitational constant is known. The motions of Earth and the Moon around their common center of mass, and the motions of spacecraft around the Moon, both carry information about lunar mass.

The NASA fact sheet includes a related quantity called GM, the product of the gravitational constant and mass, listed for the Moon as 0.00490 x 10 to the power of 6 cubic kilometers per second squared. That quantity is often measured more directly than mass itself, because spacecraft tracking measures how strongly a body pulls on a passing craft. Dividing GM by the gravitational constant gives mass. The measurement is indirect, but it is not a guess. It rests on timed observations of positions and speeds, which can be made very precisely.

Tracking also reveals uneven mass distribution. When a spacecraft passes over a denser region, its speed changes by a tiny amount. Recording those changes over many orbits builds a picture of where mass is concentrated, which refines the total mass estimate. Readers comparing sources may therefore see 7.3 x 10 to the power of 22 kilograms in one place and 7.35 x 10 to the power of 22 kilograms in another. Both are rounded versions of the same modern estimate, and the difference is a matter of how many figures are kept.

What Changes the Answer, and What Does Not

Short term changes to the Moon’s mass from everyday events are negligible for the figures in this article, because the amounts involved are tiny compared with a total mass of about 7.35 x 10 to the power of 22 kilograms. The mass figure should therefore be treated as stable for ordinary purposes, while scientists still refine the later decimal places as tracking improves.

What does change a weight answer is the setting. Move the same person from Earth to the Moon, and the weight drops to about 16.5 percent. Move the same person to a place with no nearby gravity, and the scale reading drops toward zero, even though the person’s mass is unchanged. None of those changes means the person gained or lost matter. They mean the force acting on a constant mass has changed.

Clothing and equipment also matter, because they cause confusion in lunar weight stories. An astronaut’s total weight on the Moon includes the astronaut plus the suit, backpack, tools, and any samples being carried, because the calculation must include every mass being pulled down. If a story gives a lunar weight without saying whether the suit is included, the number cannot be compared directly with a bare body weight on Earth. The rule remains the same: add all masses first, then multiply by lunar gravity.

Scales need care for the same reason. A spring scale brought from Earth to the Moon and read without recalibration would show about one sixth of the Earth reading, which is correct as a weight reading, but it would be wrong if it were read as a mass in kilograms. Mission equipment is therefore specified in mass, in kilograms, rather than in a weight that would change with location.

Common Mistakes to Avoid

First, do not state a mass figure in kilograms and call it a weight. The correct phrasing is “the mass of the Moon is 7.35 x 10 to the power of 22 kilograms.” If a weight is meant, the unit should be newtons, and the location should be stated. Second, do not quote pounds without being clear about everyday use. This article uses pounds in the everyday sense for personal weights, meaning the number a bathroom scale would show, and it uses kilograms and newtons for formal physics statements. Third, do not treat one sixth as exact. The fact sheet ratio is about 0.165, not exactly 0.1667, and local gravity varies slightly. One sixth is fine for everyday conversions, while 0.165 is better for a precise worked example.

Fourth, do not assume that lower weight means lower mass, and therefore that everything about motion becomes six times easier. Weight affects lifting and pressing down. Mass affects starting, stopping, and turning. A heavy object on the Moon still has the same inertia, so it still resists changes in motion. Fifth, do not read an orbiting astronaut’s apparent weightlessness as proof that mass has disappeared. An astronaut in orbit still has mass, and still needs force to change direction. The sensation of weightlessness comes from free fall, not from a loss of matter. The Moon itself is in a similar situation on a much larger scale: it is in free fall around Earth, which is why it has no simple scale weight in orbit, even though its mass is enormous.

Using the Numbers in Practice

To find a personal lunar weight, follow three steps. First, find a current Earth weight, in pounds, from a scale on Earth, and decide whether clothing or equipment should be included. Second, multiply that number by 0.165, or divide by 6 for a quick estimate. Third, remember that the result is a weight, while the person’s mass in kilograms has not changed. If the starting value is a mass in kilograms, the lunar weight in newtons is that mass multiplied by 1.62. If the starting value is a weight in newtons on Earth, the lunar weight is that value multiplied by 0.165.

Examples make the method concrete. A child who weighs 60 pounds on Earth would weigh about 9.9 pounds on the Moon. A teenager who weighs 110 pounds on Earth would weigh about 18.2 pounds on the Moon. An adult who weighs 175 pounds on Earth would weigh about 28.9 pounds on the Moon. For metric readers, a person with a mass of 50 kilograms weighs about 490 newtons on Earth and about 81 newtons on the Moon. A person with a mass of 80 kilograms weighs about 784 newtons on Earth and about 129.6 newtons on the Moon. A person with a mass of 100 kilograms weighs about 980 newtons on Earth and about 162 newtons on the Moon.

A reader who only needs the quick rule can take it from the Short Answer box.

FAQ

What is the mass of the Moon?

The mass of the Moon is about 7.35 x 10 to the power of 22 kilograms, using the rounded form of the NASA value of 0.07346 x 10 to the power of 24 kilograms. That is about 73.5 quintillion metric tons, about 1.62 x 10 to the power of 23 pounds of mass, and about 1.23 percent of the mass of Earth.

Does the Moon have a weight?

The Moon has a mass, which is fixed. It does not have a single weight, because weight is a force that depends on gravity. In orbit, the Moon is in free fall, so it does not press on a scale. A weight figure for the whole Moon only becomes meaningful when a gravitational setting is named.

How much would the Moon weigh on Earth?

As a hypothetical calculation, the mass of the Moon multiplied by Earth surface gravity of 9.80 meters per second squared gives about 7.20 x 10 to the power of 23 newtons. This is a thought experiment, not a measurement that has been made.

How much would the Moon weigh on its own surface?

Using lunar surface gravity of 1.62 meters per second squared, the same mass multiplied by lunar gravity gives about 1.19 x 10 to the power of 23 newtons. This is also hypothetical, and it is about one sixth of the Earth hypothetical figure.

How much would I weigh on the Moon?

Multiply your Earth weight in pounds by 0.165, or divide it by 6 for a quick estimate. A person who weighs 150 pounds on Earth would weigh about 24.8 pounds on the Moon. Your mass in kilograms would stay the same. If you know your mass in kilograms, multiply it by 1.62 to get your lunar weight in newtons.

Why is lunar gravity only about one sixth of Earth gravity if the Moon is only about one eighty-first of Earth by mass?

Surface gravity depends on mass and on radius. The Moon’s radius is about 0.2727 times Earth’s radius, so a surface object is much closer to the Moon’s center than a surface object on Earth is to Earth’s center. That closeness partly offsets the smaller mass, giving a surface gravity ratio of about 0.165 even though the mass ratio is about 0.0123.

Is the one sixth rule exact?

No. It is a rounded shorthand. The NASA fact sheet values give a ratio of 1.62 divided by 9.80, which is about 0.165, or about 16.5 percent. Local gravity also varies slightly across the lunar surface because mass is not evenly distributed. For everyday conversions, one sixth is fine. For a precise worked example, use 0.165.

Does my mass change on the Moon?

No. Mass is the amount of matter in your body, and it does not change with location. Only your weight, the force of gravity on that mass, changes. A scale that reports mass would need to be calibrated for lunar gravity to give the same mass reading on the Moon as on Earth.

How do scientists know the mass of the Moon if they cannot weigh it?

Scientists infer mass from motion. Orbits and spacecraft tracking reveal how strongly the Moon pulls on other bodies, which gives its gravitational parameter, GM. Dividing GM by the gravitational constant gives mass. Tracking also reveals uneven mass distribution, such as mascons beneath lunar basins, which refines the estimate.

What is the difference between kilograms and newtons in this article?

Kilograms measure mass. Newtons measure weight as a force. When this article says the Moon has a mass of about 7.35 x 10 to the power of 22 kilograms, it is describing matter. When it says a hypothetical Earth measurement would give about 7.20 x 10 to the power of 23 newtons, it is describing a force.

Sources & references

• NASA National Space Science Data Center, Moon Fact Sheet, by Dr. David R. Williams, NASA Goddard Space Flight Center. Values used: Moon mass 0.07346 x 10 to the power of 24 kilograms, Earth mass 5.9724 x 10 to the power of 24 kilograms, Moon to Earth mass ratio 0.0123, Moon mean density 3,344 kilograms per cubic meter, Earth mean density 5,514 kilograms per cubic meter, Moon volumetric mean radius 1,737.4 kilometers, Earth volumetric mean radius 6,371.0 kilometers, Moon surface gravity 1.62 meters per second squared, Earth surface gravity 9.80 meters per second squared, Moon volume ratio 0.0203, Moon GM 0.00490 x 10 to the power of 6 cubic kilometers per second squared. Page: https://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html
• NASA Glenn Research Center, Moon, Beginners Guide to Aeronautics. Values used: Moon mass about 8.1 x 10 to the power of 19 tons, mean diameter 2,159 miles or 3,476 kilometers, average surface gravitational acceleration 1.62 meters per second squared or 0.165 Earth gravity, average orbital distance about 240,000 miles or 384,000 kilometers, mascons beneath lunar basins and center of mass displaced several kilometers toward Earth. Page: https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/moon/
• University of California, Santa Barbara, UCSB Science Line, answer on weight and mass. Points used: mass is constant across locations, weight equals mass multiplied by gravitational acceleration, lunar gravity is about one sixth of Earth gravity, and a scale reading on the Moon is about one sixth of the Earth reading, with examples dividing Earth weight by 6. Page: http://scienceline.ucsb.edu/getkey.php?key=732