My favorite way is to look in the mirror — if you like what you see, you're fine! Fortunately, there's a more "scientific" method than visual inspection, and it's called BMI, or Body Mass Index. In the old days, we used the Metropolitan Life Insurance weight-height tables, but these were cumbersome and not always easy to find. They also didn't give you a sense of "how" overweight or underweight you might be — just that you were out of the so-called "ideal range."
The advantage of the BMI calculator is that it gives you a single number — you plug in your weight and height and it does the calculation for you. Regardless of sex or age, a "healthy weight" falls between a BMI of 18.5 and 24.9. A BMI of 25 or higher is considered overweight and anything over 29.9 is considered obese. You can find a BMI calculator just about anywhere online (my favorite place is nhlbisupport.com/bmi/).
The problem with the BMI, however, is that it doesn't take body fat into account. A very muscular football player, for example, with only 10 percent body fat would still measure well into the "overweight" division, even though most of his weight is healthy muscle. The BMI assumes a "normal" muscle distribution, so athletes and active people with some muscle should take the measurement with a grain of salt.