The world's biggest economy sizes are USA: $28.7 trillion, China: $18.5 trillion, Germany: $4.6 trillion, Japan: $4.1 trillion, California: $4 trillion, India: $3.9 trillion, and the UK: $3.5 trillion. Remarkably, California alone ranks as 5th largest economy in the world, surpassing entire countries like India and the UK. This highlights the state's incredible economic power and global influence.