A cloud weighs around a million tonnes. A cloud typically has a volume of around 1km3 and a density of around 1.003kg per m3 – that's a density that’s around 0.4 per cent lower than the air surrounding it. ☀️

Well-supported — high-quality sources agree

What we can confirm

The claim is broadly correct: multiple authoritative and reputable sources state that a typical cumulus cloud has a volume around 1 km3 and contains about 0.5 g of water per m3, putting its water content at roughly 500,000 kg (about 500 tonnes) and its total mass/weight often described as about 1 million tonnes when including the surrounding air in the cloud volume. The specific density figure of about 1.003 kg per m3 and the statement that this is about 0.4% lower than surrounding air are also directly supported by BBC Science Focus, and the United States Geological Survey gives the same order-of-magnitude result for cloud weight.

Sources

Checked July 1, 2026