During the annual weigh-in, keepers weigh and measure around 200 different species.
Zookeepers at the London Zoo have employed some crafty tactics to measure animals for this year's weigh-in.
By hanging breakfast from a tree, keepers made Asiatic lions stretch beside a big measuring stick to reveal their heights. The gorillas fell for a similar trick as they reached for treats placed on a tree.
Read: Panda Cubs Celebrate Their Second Birthdays
In other corners of the zoo, penguins walked across a scale as they lined up for food from a bucket, and goats were also lured onto the scale with the promise of a treat.
During the annual weigh-in, which began Thursday, keepers weigh and measure around 200 different species before the results are put into a database that's shared with zoos around the world.
The zoo's heaviest animal is a giraffe that weighs 1,800 pounds, while the lightest are leaf cutter ants, which weigh around 0.00001 of a pound.
Read: Burn Victim Cheered Up by Orangutan: 'He Really Made My Day'
Zoological manager Mark Habben said the weigh-in helps staff determine whether the youngest animals are growing properly and by comparing weights with the same time last year, they can determine if the animals' diets need to be changed.
The weigh-in also reveals whether some of the animals are pregnant, he said.
Watch: Zoo Holds Gender Reveal Party for Red Panda
