Zacheyp, I personally feel that a betta requires at least a 2.5 gallon tank.
1 gallons are extremely difficult to heat consistantly, and you'd need to do a 100% water change every two days. They're small, and honestly a betta would end up feeling cramped in there.
2 and a half gallon tanks only need one 50% and one 100% water change a week, they're larger, and easier to heat. Seeing as betta's enjoy swimming and moving and exploring, having a larger tank with more room for decor would help keep your boy fit and happy.
You could technically fit a betta in a 1 gallon if you wanted, but the goal of fish keeping is to make sure your betta thrives, not just survives.