If i weight 165lbs.how many calories a day do I need to lose weight?

I will not support losing weight by cutting down on calories. There are 3 ways by which you can burn your weight:

1) Doing cardio exercises: These exercise burn calories when you are doing them. No calories or fat burnt after you stop.

2) Strength training: They help in 2 ways. Building lean muscles that in turn burns calories and also burning the calories during and after your work out.

3) Reducing the calorie intake: This should be the last method. you have to ensure that you are taking proper carbs and fat in your diet and keeping a watch on the same.

3500 Cal is equal to 1 pound of fat. So depending on how you burn / reduce the calories you can reach your target weight.