How to use the BMI calculator
- Choose US (ft, in, lb) or Metric (cm, kg). Your numbers convert when you switch.
- Enter your Height: feet and inches in US units, or centimeters in metric.
- Enter your Weight in pounds or kilograms.
- Read your BMI, your category, and the healthy weight range for your height. The result updates as you type, and Calculate BMI recalculates on demand.
How BMI is calculated
BMI is your weight in kilograms divided by your height in meters squared. In pounds and inches, the same number is weight × 703 ÷ height squared. For adults 20 and older, the CDC weight categories are:
- Under 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25.0 to 29.9: overweight
- 30.0 and above: obesity, split into Class 1 (30.0 to 34.9), Class 2 (35.0 to 39.9) and Class 3 (40.0 and above)
BMI is rounded to one decimal and that rounded number picks the category, so what you see always matches. The healthy range runs from the lightest to the heaviest whole pound (or tenth of a kilogram) that still shows a BMI of 18.5 to 24.9, so it agrees with the category. At 5 ft 9 in, 168.8 lb still shows 24.9 and counts as inside, even though the range ends at 168 lb.
Worked example
With the starting inputs, 5 ft 9 in and 160 lb, height is 69 inches (1.7526 m) and weight is 72.57 kg. BMI = 72.57 ÷ (1.7526 × 1.7526) = 72.57 ÷ 3.0716 = 23.6, which the tool labels Healthy weight. The healthy range for that height is 125 to 168 lb, and the note under it reads "Your weight is inside the healthy range."
Limits and edge cases
BMI is a screening number, not a diagnosis. It cannot separate muscle from fat or show where fat sits, so a strong, lean person can read as overweight. For a closer look, try the body fat calculator or the waist-to-hip ratio calculator.
The categories are for adults 20 and older and are less reliable during pregnancy. Heights from 3 ft to 9 ft (91 to 275 cm) and weights from 22 to 1,400 lb (10 to 635 kg) are accepted, and anything else shows an error next to the field. To compare your weight with other formulas, use the ideal weight calculator, and to plan what to eat, the calorie calculator. More detail: how to calculate BMI.
Frequently asked questions
What is a healthy BMI?
For adults 20 and older, the CDC calls a BMI from 18.5 to 24.9 a healthy weight. Below 18.5 is underweight, 25.0 to 29.9 is overweight, and 30.0 or higher is obesity. BMI is one screening number, so a healthy value does not guarantee good health.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. For 160 lb at 69 inches that is 160 × 703 ÷ (69 × 69) = 23.6. This calculator does the same math and also accepts kilograms and centimeters.
Is BMI accurate for athletes or muscular people?
Not always. BMI uses only height and weight, so it cannot tell muscle from fat, and a muscular person can land in the overweight range with low body fat. A body fat estimate or waist measurement gives a better picture.
Do men, women, and older adults use different BMI categories?
The CDC uses the same cutoffs for all adults 20 and older, even though women tend to carry more body fat than men at the same BMI. For Asian adults, a 2004 WHO expert consultation also pointed to lower action points of 23 and 27.5.
Can I use this BMI calculator for children and teens?
No. For children and teens the CDC compares BMI with growth charts by age and sex and reports a percentile, not the adult categories used here. Ask a pediatrician about a child's BMI.
Sources: CDC, Adult BMI Categories; WHO Expert Consultation, Lancet 2004;363:157-163. This page is for information and is not medical advice.