你好 (ni hao) = hello 您好 (nin hao) = hello (formal) 大家好 (da jia hao) = hello everybody You use "大家好" when you are addressing several friends (casual). When you are not sure about their status you should use "你们好" (ni men hao) or "您们好" (nin men hao) to greet several people the formal way.

you can say 你好 to me,but u can only say 大家好 to more than one people,like the teacher can say 大家好 to his students at his class.

Hello Sandee, Cherry‘s answer is quite right. In addition,we use "你好"and"您好（showing respect to the person you’re speaking to）"to greet one person,and we use "你们好""大家好"to greet two or more people.But we don't use "您们好"，because it's a wrong form.

the difference between "你们好" and "大家好" is trivial, "你们好" is usually used in front of a small group of people, "大家好" is more used in front of a large group of people. and "你们好" is a little more casual, "大家好" is a little more formal. e.g. the compere of a show or TV program usually say "大家好" usually at the beginning. a speech in the class or in front of audience usually begin with "大家好". But when you see several close friends at a party or in a restaurant, you'd better say "你们好".

Hello Sandee, Your question could be rather a comparison between 你们好 and 大家好. In this case there is no difference between them,it is just another way to say the same as in " how are you (plural you)" and " how is everyone?"