What Are Clouds Made Of? (And How Do They Stay Up There?)

Looking Up at the Floating Oceans

Most of us spend our childhoods looking at the sky and seeing shapes. We see dragons, pirate ships, and giant cotton balls. But as you get older, the poetry of the sky gives way to a very practical physics question. If you have ever been caught in a torrential downpour that flooded your street in a matter of minutes, you know water is incredibly heavy. So how does an entire lake of water just float peacefully above our heads without crashing down all at once?

I remember standing on my back porch on the afternoon of May 14, 2018. A massive supercell thunderstorm was rolling across the Plains. The sky turned an eerie, bruised purple. The sheer physical mass of the storm was terrifying. It looked like a solid mountain of grey rock suspended just a few thousand feet in the air. That afternoon I had to explain to my panicked neighbor that the massive dark structure overhead was not a solid object ready to crush us. It was just water, dust, and temperature.

I am Lena Thornton. I have spent years tracking severe weather and explaining atmospheric science to people who just want to know if they need to bring their patio furniture inside. Today we are going to break down the exact mechanics of what clouds are made of and why they defy gravity. We are going to look past the bedtime stories and look at the real types of clouds that dictate our daily lives. Grab a cup of coffee. We are going to make atmospheric physics make sense.

The Invisible Ingredients: What Exactly Are Clouds Made Of?

To understand what a cloud is made of, you have to understand that the air around you is never truly empty. Even on the clearest, driest day, the sky is full of ingredients waiting for the right trigger. The National Center for Atmospheric Research has an excellent breakdown on how clouds form, but the concept is simpler than most textbooks make it seem.

A cloud is composed of three things. The first is water vapor. This is water in its gas form. It is completely invisible. Every time you exhale on a cold morning, you see a tiny cloud form. That happens because the invisible water vapor from your lungs hits the cold air and changes state. The atmosphere is packed with this invisible vapor evaporating off oceans, lakes, and even the sweat on your skin.

The second ingredient is something meteorologists call “Cloud Condensation Nuclei.” This is a fancy term for microscopic garbage in the air. Water vapor is picky. It refuses to turn back into a liquid unless it has a solid surface to grab onto. So it looks for tiny floating particles. This can be dust blown up from a desert, sea salt sprayed from ocean waves, smoke from a forest fire, or pollution from a factory exhaust pipe. According to research published by NASA, clouds that form in polluted air actually look different because they have more particles to grab onto.

The third ingredient is a drop in temperature. Warm air can hold a massive amount of invisible water vapor. But as that warm air rises into the sky, the atmospheric pressure drops. This causes the air to expand and cool down. Cold air is very bad at holding onto water vapor. Once the air cools past a certain point known as the “dew point,” the vapor is forced to turn back into a liquid. It grabs onto the nearest piece of floating dust and creates a microscopic droplet.

Multiply that tiny droplet by a few trillion, and suddenly you have a fluffy white cumulus cloud floating over your house.

Are Clouds Liquid, Gas, or Solid?

This is the question that trips up almost everyone in high school science class. Because they look so fluffy and float in the air, most people assume clouds are made of gas. That is entirely false.

The invisible water vapor floating around your living room right now is a gas. But a cloud is visible. You can see it precisely because the water is no longer a gas. The vast majority of the clouds you see on a warm summer day are entirely liquid. They are made of billions of tiny, perfectly round spheres of liquid water.

However, the higher you go in the atmosphere, the colder it gets. The wispy, feather-like cirrus clouds that you see very high in the sky are not liquid at all. At 25,000 feet, the air temperature is well below freezing. Those clouds are completely solid. They are made entirely of microscopic ice crystals reflecting the sunlight. So the answer to the question is a bit of a trick. A cloud is never a gas. It is either a massive floating collection of liquid droplets, a floating collection of solid ice, or a mixture of both if the storm is tall enough.

The Elephant in the Sky: How Heavy is a Cloud?

If clouds are just liquid water and solid ice, they must have actual mass. This is where the math gets incredibly fun. When you look up at a nice, fair-weather cumulus cloud on a sunny afternoon, you are looking at an object that has an astonishing amount of weight.

Meteorologists calculate the water density of a typical cumulus cloud to be about half a gram of water per cubic meter. That sounds very small. It is roughly the weight of a single dried pea spread out over an area the size of a large refrigerator. But a single cloud is absolutely enormous. A standard cumulus cloud is about one kilometer across and one kilometer tall. That is one billion cubic meters of volume.

When you multiply that half a gram by one billion, you get 500,000 kilograms of water. Translated into pounds, that single fluffy white cloud hovering over your neighborhood weighs about 1.1 million pounds. To put that into perspective, 1.1 million pounds is the equivalent of 100 fully grown elephants floating directly over your house. And that is just a friendly, sunny day cloud. A dark, towering cumulonimbus storm cloud packs millions of tons of water. If you want a deeper look at the specific categories, NOAA has a great breakdown of cloud classifications and their typical densities.

How Do Clouds Float If They Are So Heavy?

This brings us to the most common question people search for online. How does a million pounds of water stay in the sky without instantly crashing to the earth? The answer lies in the microscopic size of the droplets and the powerful force of rising air.

Think about a speck of dust floating in a sunbeam in your living room. Gravity is pulling that dust down, but it falls incredibly slowly because it has a lot of surface area compared to its tiny weight. The air resistance pushes back against it. This is called “terminal velocity.” The water droplets inside a cloud are even smaller than that speck of dust. A typical cloud droplet is only about 10 microns across. That is one hundred times smaller than a single raindrop.

Because these droplets are so microscopic, their terminal velocity is virtually zero. They fall at a rate of about one centimeter per second. But the atmosphere is never perfectly still. The sun heats the ground, and the ground heats the air right above it. Warm air is less dense than cold air, so it naturally rises. These columns of rising warm air are called thermal updrafts.

You can picture the process like a hair dryer pointing straight up at a ping pong ball. The ping pong ball has weight, but the upward push of the air keeps it floating. The updrafts beneath a cloud push upward at several meters per second. This easily overpowers the tiny downward fall of the microscopic droplets. As long as the warm air keeps rising from the surface, the million-pound cloud stays happily suspended in the sky. If you are learning how to read local weather patterns, understanding these updrafts is step one. You can visit our weather education hub to learn more about how surface heating drives your local daily forecast.

The Physics of Floating Water

Clouds can look like castles made of cotton candy, or they can be thin and wispy. But have you ever wondered what clouds actually are? This video provides a brilliant visual breakdown of the condensation process and the thermal updrafts that keep these massive structures in the sky.

What If We Touch a Cloud? Does It Feel Wet?

People ask me all the time, “Can you touch a cloud?” The answer is an absolute yes. In fact, there is a very good chance you already have. You just called it something else.

A cloud that forms at ground level is called fog. Fog is biologically and chemically identical to the clouds floating ten thousand feet above your head. The only difference is its altitude. When warm, moist air blows over a cold lake or a chilled valley floor, the air temperature drops to the dew point right there on the ground. The invisible water vapor turns into microscopic droplets clinging to dust particles right in front of your face.

So, what does a cloud feel like? If you have ever walked through a dense morning fog, you know the exact sensation. It feels damp, chilly, and a little bit clammy. It does not feel like a soft pillow. Because a cloud is made of liquid water droplets, walking through one leaves a fine layer of moisture on your skin, your hair, and your clothing. When skydivers freefall through a dense cloud layer, their jumpsuits often come out completely soaked on the other side. They are literally swimming through an ocean suspended in the sky.

What is the Lifespan of a Cloud?

We tend to look at clouds as permanent objects drifting across the sky. But the reality is far more dynamic. A cloud is not a static object like a balloon. It is a visible process happening in real time. For a deeper look at the astronomical mechanics of this, Space.com highlights how clouds form and dissipate rapidly across different atmospheres.

The lifespan of a typical fair-weather cumulus cloud is incredibly short. Most of them only last between ten and fifteen minutes. This is because the atmosphere is a constant battleground between evaporation and condensation.

The warm thermal updraft pushes moisture upward, creating the cloud. But as the cloud gets pushed higher, it hits drier air. The dry air surrounding the cloud acts like a sponge, pulling the microscopic water droplets back into invisible water vapor. You can actually sit on your porch and watch this happen. If you focus on a single puffy cloud on a summer afternoon, you will see the edges constantly boiling, shifting, and dissolving. The cloud is constantly dying on the outside while being rebuilt by new moisture pushing up from the inside. Eventually, the updraft runs out of energy, the dry air wins the battle, and the cloud completely vanishes into thin air.

The Breaking Point: Why Clouds Finally Fall

If the thermal updrafts are so strong, why does it ever rain? The 1.1 million pounds of water floating above your house does not stay suspended forever. Eventually, the physics equation tips in favor of gravity. But the process of turning a floating cloud into a torrential downpour is surprisingly complex.

Inside a cloud, those microscopic water droplets are constantly bouncing around in the turbulent air. As they bump into each other, they merge. This process is called collision and coalescence. Two tiny droplets hit each other and become one slightly larger droplet. Then that larger droplet bumps into three more, growing heavier with every collision. If you want a fantastic and very simple visual of how this works at a basic level, NASA provides an excellent explanation showing how water droplets group together.

A standard cloud droplet is about 10 microns wide. But a typical raindrop is about 2,000 microns wide. That means it takes about one million cloud droplets colliding together to create a single drop of rain heavy enough to fall to the earth. Once the droplet reaches that critical mass, the upward push of the warm air is no longer strong enough to hold it up. Gravity wins the tug of war, and the water falls.

In colder climates, or high up in towering cumulonimbus clouds, the process is slightly different. The top of the storm is entirely made of ice crystals. These ice crystals act like magnets for nearby water vapor. The vapor freezes directly onto the ice crystal, making it heavier and heavier until it falls as a snowflake. If it falls through a layer of warm air near the ground, it melts and hits your roof as cold rain. This is why a summer thunderstorm in Texas still technically starts as a blizzard twenty thousand feet in the air.

Why Are Some Clouds White and Others Dark Grey?

If all clouds are made of the exact same water droplets and ice crystals, why do they look so different? The answer is not about what the cloud is made of. The answer is entirely about shadows and sunlight.

A thin, fluffy cumulus cloud looks brilliantly white because it scatters sunlight perfectly. The microscopic liquid droplets act like millions of tiny prisms. When the white light from the sun hits the top of the cloud, those droplets bounce the light in every single direction. By the time the light reaches your eyes on the ground, it still contains all the colors of the spectrum mixed together. Our brains process that mixture as pure white.

But when a storm is brewing, the cloud gets incredibly thick. A cumulonimbus cloud can be up to ten miles tall. The sunlight hits the top of the cloud and starts bouncing around just like normal. However, because the cloud is so incredibly dense with water, the light is absorbed and scattered before it can reach the bottom. By the time you look up at the base of the storm, almost zero sunlight is making it through to your eyes. The cloud is not actually dark grey or black. It is just casting a massive shadow on its own stomach. If you were flying in an airplane above that exact same terrifying dark storm, the top of it would look blindingly white in the sunshine.

The Global Thermostat: Why Clouds Are Critical for Survival

Up to this point we have focused on what a single cloud is made of and how it floats over your house. But if you zoom out and look at the entire planet, clouds serve a much larger purpose. They are the ultimate temperature regulators for the Earth. Without them, our planet would experience wild, unlivable temperature swings every single day.

During the day, clouds act like a massive reflective sunshade. We talked earlier about how the tops of clouds are brilliantly white because they scatter sunlight. That process is called the “albedo effect.” A thick layer of stratocumulus clouds reflects a huge portion of the sun’s harsh solar radiation back into deep space before it can ever reach the ground. If you have ever been standing in the blazing summer sun when a thick cloud suddenly rolls over, you know exactly how powerful this cooling effect is. The temperature can drop ten degrees in a matter of seconds. If we did not have clouds reflecting that energy away, the oceans would boil and the land would bake.

At night, the clouds perform the exact opposite function. They act like a thick thermal blanket. The ground absorbs heat from the sun all day long. When the sun sets, the ground tries to radiate that heat back out into space. But if there is a thick layer of clouds overhead, the microscopic water droplets absorb that outgoing heat and trap it near the surface. This is why a cloudy winter night is often much warmer than a perfectly clear winter night. On a clear night, all the heat escapes into the upper atmosphere, causing frost to form on your windshield. To predict when this will happen in your own yard, you can learn how to read a weather map to spot incoming moisture fields.

This constant balancing act is what keeps the Earth habitable. As thermal updrafts push moisture higher into the sky, the clouds spread out and manage the heating and cooling of the entire globe. Understanding how this pressure works is fundamental to meteorology. You can dive into our guide on what barometric pressure is to see how these massive air columns move across the continents.

Lena’s Expert Note: The Flat Bottom Rule

You do not need an expensive radar system to do a little bit of backyard meteorology. If you want to impress your friends at your next barbecue, I want to teach you the Flat Bottom Rule. The next time you see a sky full of puffy cumulus clouds, look closely at their shape. The tops will be bumpy and look like cauliflower. But the bottoms will be perfectly flat. They will look like someone took a massive knife and sliced the bottom of the cloud clean off.

That flat base is not a coincidence. It represents the exact altitude where the temperature drops to the dew point. Meteorologists call this the Lifted Condensation Level. Every single cloud in that specific layer of the sky will have a flat bottom at the exact same height. If the air is very dry, that flat line will be incredibly high up in the sky. If the air is incredibly humid, that flat line might be resting just a few hundred feet above your roof. If you want to understand how this moisture translates into violent storms, check out our deep dive into understanding dew point and storm energy.

Common Cloud Questions Answered

Because the sky is so massive and clouds look so strange, people constantly search for the exact same answers online. I have compiled the most common questions about cloud physics and provided the straightforward, scientific answers below.