You need to ask yourself if you give the person enough time to talk during a conversation. Be honest while answering this question, as it will help you a lot in knowing whether you talk a lot or not. A normal, balanced conversation is one in which everyone gets an equal opportunity to talk. Ask yourself if you give other people a chance to talk, or if you keep talking yourself, forcing others to listen. If your conversations are not balanced, then you are most likely talking too much.
Do a bit of an analysis of your conversations to know the ratio between the time that you spend talking and the time you remain quiet and listen. While a balanced conversation would require a ratio of 1:1, you will be doing just fine even if you dominate the conversation 75 percent. Anything above this percentage is a clear indication that you are talking too much.
Sit down and try to recall anything that you learnt from a recent conversation. A person is more prone to learn something during a conversation when they remain quiet and pay attention to what the other person is saying. If you do not remember learning anything, then there is a good chance that you were spending way more time talking than listening.
Observe the body language of people when you are talking too much. If you see them crossing their arms, breaking eye contact or beginning to move away while you are still talking, then you are probably talking too much and maybe need to stop.
If your conversations are frequently ending with the other person telling you that they have to leave or have someone waiting for them, then there is a chance that they are simply making this excuse to get away from you because you are talking too much.