I'm not good at math so I don't use the mathematical formula to find out my BMI. There are charts and tables available that have scales for height at one axis and weight on the other. When you locate your height and weight, you can find your BMI and know whether you are normal weight or not.
I got my chart from my doctor, you can ask your doctor for one as well. It's also possible to get them online, but make sure it is the right one for you in terms of age group and gender, otherwise it might not be accurate.
I would also suggest people to visit their doctor if they want a more detailed analysis and help with losing weight. Some people take BMI results very seriously and create their own diets to lose pounds and get in the right BMI range. I don't approve of that. I think BMI is good for confirming what we already acknowledge about our health. It can help us become more conscious and make wiser decisions. But don't condemn yourself because of your BMI results.