Your worth is something you decide for yourself. It is a scale that you make for yourself. The amount of respect you give yourself reflects on how much you let others treat you. Self-worth is more than just talent, self-esteem, etc. This is how you want to be treated, how you would like to feel about yourself, how others should see you as you want them to.

In my opinion , you know your worth by the difference you make in someone's life , environment , society and even the world :) No one is worthless . I'm sure that everyone at some point in their have done something good and worthy. If you can't think of any worthy things , remember the happiness you bring to your parents when you're born ^^ Never doubt on yourself.

Frankly you don't always know your worth. It depends on your mood. If you're depressed, sad or angry you feel worthless but when you're happy you understand your worth. Also your loved ones (friends, family etc) make you understand your worth. Experiences also help. Hope this helps you.