I just became a parent recently, so pardon me if I my question seems surprising to some of you, but how do I exactly know if my child is hungry, he is only 6 months?
Children at six months can be taught sign language, and asking for food and drink is usually the easiest thing to teach them.
Sign language for babies is easy to learn because it involves logical motions and simple ones. Asking for food is moving hand toward face as if you have food in it. Asking for more is bringing hands together with fingers touching. Saying all done is the common motion for no more (think 'safe' call for baseball hand motion). All of those are very easy to learn for a six month old.
Of course, sometimes your baby won't know she is hungry; the main way to deal with that is simply to make sure you make food available on a fairly frequent basis (every few hours at least) and see how much she wants. If she is hungry she will eat.
When a baby seems distressed in any way, hunger is one of the first working hypotheses to test. It's a good idea to take a snack with you whenever you go anywhere, and to have some easy-to-serve food handy at all times.
You'll know if he was hungry if you try serving him some food and he eats it and then feels better.
As you get to know your child better, and as he matures and develops more communication skills, it will get easier to read his cues.
My wife is an amazing woman, she can tell by a cry if our kid is tired, hungry, or needs a diaper changed. There is no "exact" way to know if your baby is hungry. When I am home alone I usually just go down the checklist. When he starts getting fussy first check the diaper, then see if he wants a bottle, then try and lay him down to sleep. Sometimes he is real fussy and doesn't want a bottle or sleep. At 6 months is around when some babies start teething. They will be fussy for no reason at all. Try giving him a piece of cold celery. He can chew on it without chocking on it. You can also try baby orajel or tylenol but we try to stay away from the medications.
Are you asking because you can't tell if you are feeding him enough or because he is always cranky?