How Much Does a Cloud Weigh? 500 Tonnes, and Why It Floats

TL;DR: How much does a cloud weigh? A fair-weather cumulus about a kilometre across carries roughly 500 tonnes of water, more than eighty of the largest African elephants, floating quietly over your head. It stays up because it is not one lump of water. It is billions of droplets, each around two hundredths of a millimetre across, sinking more slowly than the air rising past them.

Key takeaways

• How much does a cloud weigh? A cumulus one cubic kilometre in size holds about 500 tonnes of water.
• The USGS Water Science School gets to that figure from a cloud water density of roughly 0.5 grams per cubic metre.
• That water is divided between billions of droplets, each averaging 0.02 mm across, a hundredth of a millimetre in radius.
• A cloud droplet sinks at only about a centimetre a second, slower than the air rising through the cloud.
• It takes on the order of a million cloud droplets merging to build one 2 mm raindrop that can actually fall.

Last updated: 28 August 2026

How much does a cloud weigh, and how would you weigh one?

How much does a cloud weigh? Take an ordinary fair-weather cumulus as a block of cloud one kilometre on each side and the answer is about 500 tonnes of water. Nobody has put a cloud on a scale. You get there with arithmetic, from the liquid water inside each cubic metre.

How much does a cloud weigh, worked properly? The USGS Water Science School does the sum in public. Cumulus cloud water density runs at roughly half a gram per cubic metre, and a cloud of one cubic kilometre contains a billion cubic metres. Multiply the two and you have 500 million grams of droplets hanging in the sky.

1,000,000,000 x 0.5 = 500,000,000 grams of water droplets in our cloud. That is about 500,000 kilograms or 1.1 million pounds. USGS Water Science School

So how much does a cloud weigh in something you can picture? WWF puts a large male African elephant at up to six tonnes, which makes 500 tonnes more than eighty of them, and that is where the familiar hundred-elephant comparison comes from. It is drifting over the rooftops on any ordinary summer afternoon.

Why doesn’t a 500 tonne cloud fall on your head?

Because nothing up there is carrying 500 tonnes. Ask how much does a cloud weigh and you get a figure for the whole cloud, but that mass is shared out between billions of separate droplets. Each one is small enough that air resistance almost cancels its weight, so it barely falls at all.

Work out the fall speed of a typical droplet and you get about 1.2 centimetres per second, a figure set out in Practical Meteorology on Geosciences LibreTexts. Air inside a growing cumulus rises faster than that, so the droplets are carried up rather than down.

Buoyancy does the rest. The USGS points out that cloud floats because the moist air it is made of is less dense than the drier air below it, the way oil floats on water. The Met Office says the same thing from the other side: cloud is warmer than the air around it.

What is a cloud actually made of?

Water and dust, in that order. A cloud is billions of liquid droplets or ice particles suspended in air, and every droplet formed on a speck of something solid. NOAA calls those specks cloud condensation nuclei, and without them water vapour has nothing to condense onto.

The specks are smoke, sea salt, volcanic ash or wind-blown soil, and NOAA sizes them at about one hundredth of the droplet that grows around them. Every drop of rain that has hit a UK pavement began as one.

So how much does a cloud weigh in water alone? Very nearly all of it. The nuclei at the centre of each droplet are far too small to register against the water wrapped around them.

How much bigger does a droplet have to grow before it rains?

Roughly a hundred times wider. An average cloud droplet is about 20 microns across and an average raindrop about 2 millimetres, so the drop landing on your coat is around 100 times the width of the droplet it grew from. By volume that is a million droplets merging into one.

A typical cloud droplet is 20 microns in diameter, a typical raindrop is 2 millimeters (2000 microns) in diameter. UCAR Center for Science Education

That growth is the moment the arithmetic flips. At 20 microns the droplet sinks at a centimetre a second and the updraught wins easily. At 2 millimetres it falls at roughly 9 metres per second, which no ordinary rising air holds. How much does a cloud weigh matters far less than how finely that weight is divided.

Does this change how you read rainfall on a real site?

Quietly, yes. How much does a cloud weigh is a fun question, but the useful half of the answer is that the water is overhead long before it reaches a gutter or a drain. Rainfall is not an event that starts when the first drop lands. It is a store assembled hours earlier and released in minutes.

That is the instinct behind what we do at AQUAIOT. We watch water arrive and move, whether it is rain captured in an AQUAIOT Smart Water Butt, a level trend read by the AQUAIOT Radar, or the same storm arriving downstream in sewer and drainage monitoring. Our round-up of UK water facts has plenty more.

Frequently asked questions

A quick recap of the question people ask most, how much does a cloud weigh, along with the ones that tend to follow it.

How much does a cloud weigh in elephants?

How much does a cloud weigh in elephants? More than eighty of the largest ones. WWF puts a big male African elephant at up to six tonnes, so a 500 tonne cumulus is over eighty of them. The familiar hundred-elephant version assumes a five tonne adult, which is why both figures turn up.

If a cloud weighs 500 tonnes, why does it float?

Because that weight is spread across billions of droplets, not held as one mass. Each droplet is so small that it sinks at barely a centimetre a second, and the air rising through the cloud moves faster than that. The USGS adds that moist cloud air is less dense than the drier air beneath it.

How big is a cloud droplet?

About 20 microns in diameter on average, which is two hundredths of a millimetre, or a hundredth of a millimetre in radius. Cloud droplets range from roughly 2 to 50 microns. A typical raindrop is 2 millimetres across, about a hundred times wider than the droplet it grew from.

What makes a cloud finally release its water as rain?

Droplets colliding and merging until they are heavy enough to beat the rising air. It takes on the order of a million cloud droplets to build one raindrop. Once a drop reaches about 2 millimetres it falls at roughly 9 metres per second, and no ordinary updraught inside the cloud can hold it.

By Gianbattista Porru, Digital and IoT lead at AQUAIOT.