BMI Calculator
YOUR BMI
Adult BMI Category
Healthy Weight
What Is BMI?
Body mass index, or BMI, is a ratio of body weight to height. It gives a quick standardized number that can be used as a screening measure in adults.
BMI does not directly measure body fat, muscle mass or where body fat is stored, so the number should be interpreted alongside other information rather than as a complete assessment of health.
This adult BMI calculator is for people aged 20 and older. BMI for children and teenagers is interpreted using age- and sex-specific growth charts.
How It's Calculated
Body mass index is calculated by dividing body weight in kilograms by height in meters squared (BMI = kg / m²). For U.S. customary measurements, the equivalent formula is BMI = 703 × weight (lb) / height (in)². When you enter pounds and feet/inches, Need.fit converts those inputs internally before calculating the same adult BMI. For adults, the calculation uses height and weight and is applied the same way for men and women without altering the equation.
BMI = weight (kg) / height² (m²)
- Weight: kilograms (kg) or pounds (lb)
- Height: meters (m), centimeters (cm), or feet and inches
What to Do With Your Result
Treat BMI as one screening number, not as a complete description of your body composition or health. CDC defines adult BMI categories ranging from Underweight (<18.5) and Healthy Weight (18.5–24.9) to Overweight (25.0–29.9) and Obesity Classes 1–3 (30.0+).
Because BMI relies on total body weight, it cannot distinguish fat mass from muscle, bone, or water. If you have a high level of muscle mass, BMI may place you in a higher category even though your body fat percentage is low.
For an estimate based on body circumferences rather than height and weight alone, use Need.fit's Body Fat Percentage Calculator.
Need.fit combines your goals, activity, nutrition and progress with actionable fitness data instead of building an entire plan around one height-to-weight ratio.