Just by using your hands you can know how much to eat depending on your goals.
Ingredients:

Your palm and thumb

Your fist
We’ll keep it simple. There are two ways of architecting a fitness-aware plate of food:
1. Low carb
You should use this estimate for lunch and dinner if your goal is to lose weight. If you trained that day, you should eat 1 plate as Low Carb and another as High Carb.
Add the following to your plate:
- 1/2 palms of protein
- 2/3 fists of vegetables
- 2/3 thumbs of fatty food - if it’s vegetable or fish oil use less than a half of a thumb as a guide for each unit; if it’s olives or dry fruits use half a fist
- 0/1 fist of starchy vegetables like potato or sweet potato
- 0/1 fist of fruit
2. High carb
You should eat both lunch and dinner as high carb if your goal is to build muscle / gain weight.
This plate should consist of:
- 1/2 palms of protein
- 1/2 fists of vegetables
- 0/1 thumb of fatty food - if it’s vegetable or fish oil use less than a half of a thumb as a guide for each unit; if it’s olives or dry fruits use half a fist
- 1/2 fist of starchy vegetables like potato or sweet potato
- 1 fist of fruit
Eating frequency
I think it’s best to have 3 big meals a day. If you feel hungry between meals you can always eat a small snack. For instance: a fist of fruit or half a fist of dry fruits. But don’t feel obliged to reach 5 or 6 meals a day, just eat those 3 big meals using the guidelines mentioned above, and, if you do feel hungry, have a snack or two.