You don't gain calories from sitting. You gain calories from eating.
To gain one pound is 3,500 calories.
1,000,000 calories a day you a hole
It does not matter what proportion of daily calories come from breakfast.
You gain fat by eating more calories than you burn. As a teenager, you are probably still growing. You may find that while growing that you are using more calories than you are taking in. Unless you are very thin, give it some time as once you reach your adult height you will begin to gain weight. You might even wish you were thin once again.
The short answer is 7700 extra calories will make you gain 1kg of fat
400 calories
35,000 calories.
calories needed for 63 inch and 115 pound male teenager
Add 500 calories per day to gain 1 pound per week.
The only way that you gain calories would be through consuming them through food or drink.
If you are an very active teenager you should consume about 3000 to 4000 calories a day. to gain one pound a day it usually is 3200, but it depends on the body and your metabolism remember everyine is different .