This is a difficult question to answer because it changes over time.
If you eat food you will automatically gain the weight of what you just ate right away.
Give it time and your body will use some calories for energy.
More time and it passes through your system and eventually leaves your body through feces and urine.
But to permanently gain one pound of fat you have to have consumed about 3500 Kcal of energy from extra carbohydrate or fat.
The thing is over time after you eat (say 6,000 calories) its hard to estimate what you used for energy, what the weight of the food was, how much of it was excreted, how long your body held on to that food before it was totally out of your system, when the next time you ate was ect..
Also there is a large change in weight of food per calorie. To get an extra 3500 calories you would need to eat about a pound of butter or over 2 pounds of pasta and so on