If you are a boy, I suggest you go to the gym or buy some dumbbells and other fitness equipment to exercise. Increasing chest circumference is mainly to exercise pectoralis major and dorsal muscles, and the fastest effect should be pectoralis major, while dorsal muscles are more difficult to practice. According to my own experience and fitness knowledge, the most effective way for you to increase your chest muscles is to support on parallel bars, and practice three times a week for one or two days, two or three groups at a time, trying not to have strength, and supplementing nutrition within one hour after exercise (protein). You will definitely increase your chest muscles in a month. You can really see that people will be stronger and fuller. Of course, persistence is very important. This is also the most effective and economical way to practice bodybuilding for the first time. If you are willing to spend money, you can sign up for a gym or buy equipment. Both bench press and bird practice chest muscles. You can know more about me, so I won't introduce it. I hope it helps you.