Much has been written lately about the deficiencies of the Body Mass Index (BMI) for determining overweight or obesity. Without getting into a lot of detail, it comes down to this: Very fit, muscular people are often mistakenly classified as overweight because the scale and the BMI formula do not differentiate fat from muscle.
So, if the mirror and your belt size are not enough to tell you if are too fat, use the waist-hip ratio method for greater accuracy than the BMI. It doesn't require calipers or other doodads to get your answer. Just a simple cloth tape measure. Here's how to do it.
Measure the circumference of your waist (at the smallest point) and of your hips (at the largest point) and divide waist size by hip size. For example, if you are a woman whose waist is 32 inches and your hips 37 inches, you divide 32 by 37, for a ratio of 0.86. This puts you at slightly above normal. For women, a ratio under 0.85 is normal; for men, a ratio under 0.90 is normal.
I wouldn't go so far as saying that scales are obsolete, but they do not always tell the whole truth and nothing but the truth.