Animals at London Zoo are taking part in the annual weigh-in, resulting in some pretty amazing photos.
The reason the animals are measured and weighed is so that zookeepers can keep an eye on their health, according to the BBC.
London Zoo has 20,166 animals across 698 different species, so the weigh-in is a lengthy process.
Not only does this help London Zoo look after its animals, but the information is also sent to a database for zoos around the world to use to check if their animals are healthy too.
Some of the animals are small enough to be put on the scales, whereas for others it's a little harder.
Take a look at the gallery above to see how some of the animals are weighed