BMI Calculator – Check Your Body Mass Index

Body Mass Index (BMI) is a number calculated from a person's height and weight that indicates whether their weight falls within a healthy range. It is used by doctors and public health organizations worldwide as a first-line screening tool for weight-related health risks. According to the World Health Organization (WHO), a BMI of 18.5 to 24.9 is classified as normal weight for adults.

BMI does not directly measure body fat, but research consistently shows it correlates with body fat levels at a population scale. A higher BMI is associated with increased risk of type 2 diabetes, cardiovascular disease, and certain cancers.

Metric:

BMI = weight (kg) ÷ height² (m²)

Imperial:

BMI = (weight in lbs × 703) ÷ height² (inches²)

Worked example: A person who is 5'9" (175 cm) and weighs 160 lbs (73 kg) has a BMI of 23.8 — which falls in the normal weight range.

1. Select your unit system — choose Metric (cm, kg) or Imperial (ft, lbs).
2. Enter your height — in centimeters (e.g., 170) or feet.inches (e.g., 5.8 for 5'8").
3. Enter your weight — in kilograms or pounds.
4. Add age and gender (optional) — enables more personalized recommendations.
5. Click "Calculate My BMI" — your BMI score, category, ideal weight range, and health guidance appear instantly.

All calculations run locally in your browser. No personal data is stored or shared.

BMI is a useful screening tool, but it has real limitations that are important to understand before acting on your result.

• Muscle mass is invisible to BMI. A 200 lb bodybuilder and a 200 lb sedentary person can have identical BMI scores but very different health risks. BMI consistently overestimates obesity risk in athletes and strength-trained individuals.
• Where you carry fat matters more than total fat. Waist circumference is a stronger predictor of cardiovascular risk than BMI alone. A "normal" BMI with a large waist (above 35 inches for women, above 40 inches for men) still indicates elevated metabolic risk.
• Ethnic differences are clinically significant. The WHO recommends a lower overweight threshold of 23.0 for some Asian populations due to higher metabolic risk at lower BMI values.
• BMI does not apply to children. Anyone under 18 requires pediatric BMI percentile charts, not adult BMI categories.

For a more complete picture of health, pair your BMI result with a body fat percentage measurement or waist-to-height ratio.

• Target a calorie deficit of 300–500 calories per day — this rate achieves sustainable fat loss (roughly 0.5–1 lb per week) without significant muscle loss.
• Add resistance training 2–3 times per week — preserving muscle during weight loss keeps metabolism higher and improves body composition even at the same BMI.
• Prioritize protein (1.6–2.2g per kg of body weight) — higher protein intake reduces hunger and protects lean mass during a calorie deficit.
• Track waist circumference alongside BMI — a waist above 35" (women) or 40" (men) is an independent cardiovascular risk signal regardless of BMI category.
• Aim for 7–9 hours of sleep — NIH research shows sleep deprivation raises hunger hormones and increases daily calorie intake by an average of 300 calories.