If you live in a city large enough to have a basketball team and a football team (Americans), then generally your basketball court is an arena and your football field is a stadium. That is a good general idea of their relative size.
She has already made stadium concerts ignorants ... she sold out 2 concerts in Mexico D.F. with capacity of 60.000 people and 1 in Guadalajara, which more than 30.000 people attended . Wait until she comes to South America , she will sold out every single concert. People here is f***ing wild for watching Lady Gaga live next year.