BMI Index Calculator
Calculate your Body Mass Index instantly.
Free BMI Index Calculator
Calculate your Body Mass Index (BMI) using our accurate BMI index calculator. Simply enter your height and weight to instantly see your BMI value, weight category, and health recommendations. Our calculator uses WHO standards and provides detailed analysis of your results.
BMI Index Categories
- • Underweight: BMI < 18.5
- • Normal weight: BMI 18.5-24.9
- • Overweight: BMI 25-29.9
- • Obese: BMI ≥ 30
Important Note
BMI index is a screening tool, not a diagnostic measure. Consult healthcare professionals for comprehensive health assessment and personalized advice.
Physical Measurements
Personal Information
Your BMI
Normal weight
Healthy Weight Range
Target range
Ideal Weight
Middle of healthy range
Body Fat Estimate
Estimated percentage
Daily Calories
Maintenance calories
How it works
BMI (Body Mass Index) screens whether your weight is in a healthy range for your height. It divides weight by the square of height, scaling weight to body size for comparison against standard categories.
Body Mass Index
Metric: BMI = kg ÷ m² Imperial: BMI = 703 × lb ÷ in²
- kg / lb
- body weight
- m / in
- height (703 converts imperial units)
Worked example
- Weight 70 kg
- Height 1.75 m
- BMI = 70 ÷ (1.75)²
- BMI = 70 ÷ 3.0625
BMI ≈ 22.9 — within the normal range (18.5–24.9).
Good to know
- Categories: under 18.5 underweight · 18.5–24.9 normal · 25–29.9 overweight · 30+ obese.
- BMI can't tell muscle from fat, so very muscular people may read high despite low body fat.
- It's a population screen, not a diagnosis — pair it with waist size or body-fat percentage.
Related Calculators
Frequently Asked Questions
How is BMI calculated?
BMI divides weight by height squared: kg ÷ m² in metric, or 703 × lb ÷ in² in imperial units. A 70 kg person at 1.75 m has a BMI of 70 ÷ 3.0625 ≈ 22.9.
What are the BMI categories?
Under WHO standards for adults: below 18.5 is underweight, 18.5-24.9 is normal weight, 25-29.9 is overweight, and 30 or above is obese. Obesity is further divided into class I (30-34.9), class II (35-39.9), and class III (40+).
Is BMI accurate for everyone?
No — BMI cannot distinguish muscle from fat, so muscular athletes often read as overweight despite low body fat, and older adults can read normal while carrying little muscle. Some populations also face health risks at lower BMI thresholds than the standard cutoffs.
Is BMI calculated differently for children?
The formula is the same, but interpretation differs: children and teens are assessed by age- and sex-specific percentiles rather than fixed cutoffs, because healthy body composition changes through growth. The adult categories should never be applied to anyone under 20.
What should I use alongside BMI?
Waist circumference and waist-to-height ratio capture abdominal fat, which BMI misses, and body-fat percentage measures composition directly. BMI is a quick screening tool — health decisions should rest on a fuller picture with a healthcare professional.