BMI Calculator
Calculate Body Mass Index and see your weight category
About the BMI Calculator
This BMI calculator works out body mass index from your height and weight in either metric or imperial units, then names the World Health Organization category the result falls in. Figures are calculated in your browser and never stored or sent anywhere.
A BMI calculator divides weight by the square of height to produce a single number used as a rough screen for whether weight sits in a healthy range for a given height. Enter kilograms and centimetres, or pounds and feet and inches — the calculator handles both without converting first.
The result is shown with its WHO category: under 18.5 underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight, 30 and above obese. Those thresholds are the internationally used ones, which is why clinics and insurers quote the same bands.
BMI is a screening figure, not a diagnosis. It cannot distinguish muscle from fat, so athletes often read as overweight, and it is interpreted differently for children, pregnancy and some ethnic groups. Treat it as one input among several rather than a verdict.
How to use the BMI Calculator
- Choose your units. Switch between metric (kg and cm) and imperial (lb, ft and in).
- Enter your height. Type your height in the selected units.
- Enter your weight. Type your weight. The BMI updates as you type.
- Read the category. See your BMI value and which WHO weight category it falls in.
BMI Calculator features
- Metric and imperial unit support
- Real-time BMI calculation
- Health category classification
- Visual BMI range indicators
- Professional medical accuracy
- Adult BMI standards (WHO)
- Instant results display
- Mobile-responsive design
- Privacy-focused calculation
- Health monitoring tool
Frequently asked questions
How is BMI calculated and what does it measure?
BMI (Body Mass Index) is calculated by dividing weight in kilograms by height in meters squared (kg/m²) for metric units, or using weight in pounds and height in inches for imperial units. BMI measures body fat based on height and weight, helping assess if you're in a healthy weight range.
What are the BMI categories and what do they mean?
BMI categories: Underweight (Below 18.5), Normal weight (18.5-24.9), Overweight (25-29.9), Obese Class I (30-34.9), Obese Class II (35-39.9), Obese Class III (40+). These ranges help identify potential health risks associated with weight categories.
Is BMI accurate for everyone?
BMI is a useful screening tool but has limitations. It may overestimate body fat in athletes with high muscle mass and underestimate body fat in older adults with reduced muscle. For comprehensive health assessment, consider waist circumference, body composition, and other health indicators.
Can this calculator be used for children and teenagers?
This BMI calculator is designed for adults (18+ years). For children and teenagers, BMI percentiles are used instead of adult BMI categories, as body fat changes with growth and development. Pediatric BMI requires age and gender-specific growth charts.
How often should I check my BMI?
Check BMI every 3-6 months when actively managing weight, or annually for routine health monitoring. More frequent checks may be beneficial during weight loss programs, pregnancy, or when making significant lifestyle changes.
What should I do if my BMI is outside the healthy range?
Consult healthcare professionals for personalized advice. For underweight BMI, focus on nutrient-dense foods and strength training. For overweight BMI, consider balanced nutrition, regular exercise, and gradual weight loss. Always seek medical guidance before making significant health changes.