Mega-cities are popping up around the world as the Earth’s population continues to grow. There are now more than 8 billion people on the planet, and that number is still rising. And while India may be the most populated country, it’s not home to the world’s biggest city.
That title belongs to Japan, where nearly 40 million people live in one giant mega-city. According to the World Population Review, Tokyo is the largest city on Earth in 2025, with a population of 37,036,200. That’s nearly four times bigger than London, which ranks 37th with 9,840,740 residents.
As a result the Japanese capital also covers a huge area. BBC Science Focus says it stretches across 13,452 square kilometres, with more than 2,600 people packed into every square kilometre.
That level of crowding has led to some big housing and transport issues.
Some young people now live in flats as small as nine square metres so they can stay close to the centre.
Roads are also often gridlocked and trains are full during peak hours, but the city’s transport system is still widely praised for being fast and reliable.
Despite the issues, Tokyo remains one of the world’s most liveable cities.
It ranked 31st in the Time Out Best Cities Survey 2025, with locals rating it highly for transport, food, and quality of life. Around 70% of people said the city makes them feel good.
Tourism is also booming thanks to the weaker yen and new attractions like Tokyu Plaza Harajuku Harakado and the huge Azabudai Hills complex.
Top things to see include Shibuya Crossing, known as the world’s busiest pedestrian junction, and the Tokyo Skytree, which is the tallest structure in Japan.
Those after a quieter spot can visit Shinjuku Gyoen, a peaceful 144-acre garden with Japanese, French, and English-style landscaping.
Tokyo is also known for its food. Many consider it the birthplace of sushi, and the city is believed to have more Michelin-starred restaurants than anywhere else in the world.
So while life in the world’s largest city comes with challenges, there’s still plenty to see, do, and eat.