What is the best way to know the ideal weight?

Few ways. There are some rough estimates available, but the best ways are to be evaluated by someone who does this sort of thing to take into account height, weight, and body fat percentages. This can be done with calipers, water dispersion, etc.
BMI. You can determine your normal weight by simply using bmi formula (body mass index). Its formula is = weight (kilogram) / [ (height x height) (in meter)].