500 t1,100,000 lb
A typical fair-weather cumulus cloud holds about 500 tonnes (1.1 million lb) of water, according to NCAR scientist Peggy LeMone. That figure assumes a cloud 1 km on each side with 0.5 grams of water in every cubic metre. Other estimates put the water nearer 250 tonnes, and the air inside weighs far more.
| Water, 1 km cloud, NCAR estimate0.5 g of water per cubic metre | 500 t1,100,000 lb |
|---|---|
| Water, 1 km cloud at 0.3 g per m³Upper end of typical cumulus values | 300 t661,000 lb |
| Water, 1 km cloud, Reading estimate0.25 g of water per cubic metre | 250 t551,000 lb |
| Water, smaller cloud 500 m acrossOur calculation at 0.5 g per cubic metre | 62.5 t138,000 lb |
Nobody puts a cloud on a scale. The weight is a calculation: how much water is in each cubic metre of cloud, times how many cubic metres the cloud fills. Research aircraft flying through cumulus clouds measure about 0.5 grams of liquid water per cubic metre, roughly a small marble’s worth of water spread through each cubic metre of air.
Peggy LeMone, a scientist at the National Center for Atmospheric Research (NCAR), sizes clouds by watching her car’s odometer as she drives underneath them. A typical cumulus is about 1 km across and roughly as tall as it is wide. So 1,000 m × 1,000 m × 1,000 m = 1,000,000,000 m³, and 1,000,000,000 m³ × 0.5 g = 500,000,000 g, which is 500,000 kg or about 1.1 million lb. That is about as much as 100 elephants.
The water content of a cumulus cloud is not fixed. Typical values listed for cumulus run from about 0.25 to 0.30 g per cubic metre, lower than LeMone’s 0.5 g. Rob Thompson, a meteorologist at the University of Reading, uses 0.25 g per cubic metre and gets 250 tonnes (about 551,000 lb) for the same 1 km cloud.
Size matters even more, because volume grows with the cube of width. A cumulus 500 m across has one-eighth the volume of a 1 km cloud, so at 0.5 g per cubic metre it holds about 62,500 kg (137,800 lb) of water. A growing cloud that turns into a thunderstorm can be 10 km wide and 10 km tall with about 2 g of water per cubic metre, which Thompson puts at roughly 2 million tonnes of water.
The water is split into enormous numbers of tiny droplets. Each one is about 20 microns (0.02 mm) across, roughly one-hundredth the diameter of a raindrop, so it takes about a million of them to make one raindrop. A droplet that small falls at only about 1 cm per second, and updrafts inside a cumulus can reach several metres per second, easily enough to hold the droplets up.
It also helps to remember that the water is a tiny part of the cloud. The air in that same cubic kilometre weighs about 1 million tonnes (2.2 billion lb), roughly 4,000 times more than the water at Thompson’s figure. The cloud is mostly air that happens to carry some droplets. Rain starts only when droplets grow large enough that the updrafts can no longer support them.
A typical cumulus cloud about 1 km across holds roughly 1.1 million lb (500 tonnes) of water. Using a lower water content of 0.25 g per cubic metre, the same cloud holds about 551,000 lb.
They multiply the cloud’s volume by its water content. Aircraft measure how many grams of liquid water each cubic metre of cloud holds, and the cloud’s width and height give the volume.
A big thunderstorm cloud can be 10 km wide and 10 km tall with about 2 g of water per cubic metre. That works out to roughly 2 million tonnes (about 4.4 billion lb) of water, thousands of times more than a fair-weather cumulus.
Its water is spread out as tiny droplets about 0.02 mm across that fall only about 1 cm per second, and rising air inside the cloud holds them up. The water is also a tiny fraction of the cloud, which is mostly air.
At 500 tonnes, a typical cumulus cloud weighs about as much as 100 elephants.
Last checked October 3, 2026.
