BMI Calculator
Calculate Body Mass Index (BMI) and determine healthy weight ranges.
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Comprehensive BMI analysis with BMI Prime, Ponderal Index, children's BMI support, and health insights
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Calculate your Body Mass Index with comprehensive health insights, metabolic information, and personalized recommendations
How it works
Body Mass Index is a quick screen for whether your weight is in a healthy range for your height. It divides your weight by the square of your height, so it scales weight to body size and gives a single number you can compare against standard categories.
Body Mass Index
Metric: BMI = kg ÷ m² Imperial: BMI = 703 × lb ÷ in²
- kg
- weight in kilograms
- m
- height in metres
- lb
- weight in pounds (imperial)
- in
- height in inches (imperial); 703 converts the units
Worked example
- Weight = 70 kg
- Height = 1.75 m
- BMI = 70 ÷ (1.75 × 1.75)
- BMI = 70 ÷ 3.0625
BMI ≈ 22.9 — within the “normal” range (18.5–24.9).
Good to know
- Standard adult categories: under 18.5 underweight · 18.5–24.9 normal · 25–29.9 overweight · 30+ obese.
- BMI doesn't distinguish muscle from fat, so very muscular people can read as “overweight” despite low body fat.
- It also ignores fat distribution; waist circumference and body-fat percentage give a fuller picture.
- Children, teens, pregnant people, and older adults need age- or context-specific charts rather than the adult cut-offs.
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Frequently Asked Questions
How do I calculate my BMI?
To calculate BMI, divide your weight in kilograms by your height in meters squared (BMI = kg/m²). For imperial units, multiply weight in pounds by 703, then divide by height in inches squared. Our free BMI calculator does this instantly for you.
What is a healthy BMI range?
According to WHO guidelines, a healthy BMI range is 18.5-24.9. Below 18.5 is underweight, 25-29.9 is overweight, and 30 or above is obese. These ranges apply to most adults but may vary for athletes, elderly, and certain ethnic groups.
Is BMI accurate for everyone?
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat, so athletes may have high BMI despite low body fat. It also doesn't account for age, gender, or ethnic differences in body composition. Consider it alongside other health indicators.
What's the difference between BMI for men and women?
The BMI calculation is the same for men and women. However, women typically have more body fat than men at the same BMI. Body fat distribution also differs - men tend to store fat around the waist, while women store it in hips and thighs.
How can I lower my BMI safely?
To lower BMI safely: 1) Create a moderate calorie deficit (500-750 calories/day), 2) Exercise regularly (150+ minutes/week), 3) Focus on whole foods, 4) Stay hydrated, 5) Get adequate sleep, 6) Aim for 1-2 pounds weight loss per week. Always consult healthcare providers before major diet changes.
What health problems are linked to high BMI?
High BMI is associated with increased risk of: type 2 diabetes, heart disease, high blood pressure, stroke, sleep apnea, certain cancers, osteoarthritis, fatty liver disease, and kidney disease. However, BMI is just one factor - overall lifestyle and genetics also matter.
Can BMI be too low?
Yes, BMI below 18.5 (underweight) can indicate malnutrition and increase risk of: weakened immune system, osteoporosis, anemia, fertility issues, and growth problems in young people. If your BMI is below 18.5, consult a healthcare provider.
Should I use BMI or body fat percentage?
BMI is a quick screening tool, while body fat percentage provides more detailed body composition information. Athletes and very muscular individuals should prioritize body fat percentage. For most people, BMI combined with waist circumference gives a good health assessment.
How does age affect BMI interpretation?
BMI interpretation changes with age. For adults 65+, slightly higher BMI (25-27) may be protective. For children and teens, BMI must be compared to age and sex-specific growth charts. Muscle mass naturally decreases with age, affecting BMI accuracy.
What's the BMI formula in metric and imperial?
Metric formula: BMI = weight (kg) ÷ height² (m²). Imperial formula: BMI = (weight (lbs) × 703) ÷ height² (inches²). For example, 70kg and 1.75m = 70 ÷ (1.75 × 1.75) = 22.9 BMI.