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BMI Calculator

Body Mass Index calculator with metric and imperial units, color-coded category, healthy weight range and visual BMI scale.

Height (cm)

Weight (kg)

Age (optional)

Gender (optional)

Quick reference

Your BMI

Normal weight

Your BMI falls within the healthy range for most adults.

Healthy weight range for your height: 53.4 – 72.0 kg

BMI = 70 / (1.70)² = 24.2

WHO BMI classification (adults, 20+ years)
Category	BMI range	Weight for 170 cm
Underweight	< 18.5	< 53.4 kg
Normal weight	18.5 – 24.9	53.4 – 72.0 kg
Overweight	25.0 – 29.9	72.3 – 86.4 kg
Obesity class I	30.0 – 34.9	86.7 – 100.9 kg
Obesity class II	35.0 – 39.9	101.2 – 115.3 kg
Obesity class III	≥ 40	≥ 115.6 kg

Important: BMI limitations

BMI is a screening tool, not a diagnosis. It was designed for population studies and does not directly measure body fat.

What BMI ignores: muscle mass, bone density, fat distribution, age, sex, ethnicity. A muscular athlete may score as overweight while having very low body fat.

Who should interpret results with extra care: athletes and bodybuilders, pregnant or breastfeeding people, children and teens (need age- and sex-specific percentiles), older adults (muscle loss can hide excess body fat), people of different ethnic backgrounds (some populations have increased health risk at lower BMI values).

For a complete picture, combine BMI with waist circumference, waist-to-hip ratio, body-fat percentage, blood pressure, and a conversation with a qualified healthcare professional.

Frequently asked questions

BMI uses weight divided by the square of height. In metric units the formula is BMI = weight(kg) / height(m)². In imperial units it is BMI = 703 × weight(lb) / height(in)². Both formulas give the same number — the 703 constant just converts the units. For example, 70 kg and 1.70 m give BMI = 70 / (1.70 × 1.70) ≈ 24.2.

BMI treats all mass the same. Muscle is about 18% denser than fat, so a lean, muscular body weighs more than a softer body of the same height. Athletes, powerlifters, and people who strength-train regularly are routinely mislabeled by BMI. A body-fat percentage measurement (DEXA scan, bioimpedance, or skinfold calipers) is a better indicator in this case.

Not directly. For people under 20 years old, BMI has to be interpreted against age- and sex-specific percentile charts (for example, the CDC growth charts). A child with a BMI in the 85th to 94th percentile is considered overweight, and above the 95th percentile is considered obese. Always use a pediatric BMI percentile calculator for children rather than adult ranges.

The World Health Organization defines 18.5 to 24.9 as the normal weight range for adults. Values below 18.5 are underweight, 25 to 29.9 is overweight, and 30 or higher is classified as obesity in three sub-classes. These cutoffs were set from population data linking BMI to all-cause mortality risk.

Waist-to-hip and waist-to-height ratios measure central (abdominal) fat, which is more strongly linked to heart disease and type 2 diabetes than overall weight. A waist-to-height ratio below 0.5 is generally considered low risk. These ratios complement BMI — they do not replace it. Using both gives a clearer picture of metabolic risk than BMI alone.

For any given height, the normal BMI range corresponds to a specific weight range. The calculator above shows this as the "Healthy weight range" block. If your current weight is above the upper bound, the difference is the amount you would need to lose to reach the healthy range; if below the lower bound, it is the amount you would need to gain. Always aim for gradual changes — roughly 0.5 to 1 kg (1 to 2 lb) per week is considered sustainable.

This calculator is for informational purposes only and does not replace professional medical advice. Consult a healthcare provider for a full assessment of your health.

This BMI calculator computes Body Mass Index from height and weight and places the result on the WHO classification scale for adults. It accepts both metric (kg, cm) and imperial (lb, ft+in) input, and reports the category in six classes: Underweight (<18.5), Normal (18.5-24.9), Overweight (25-29.9), and Obesity classes I, II and III. Alongside the BMI number, the tool shows the healthy weight range for your height and the amount of weight you would need to gain or lose to reach that range. A horizontal color-coded scale with a marker makes the result visual. Optional age and gender fields adjust the interpretation text. Example: weight 70 kg, height 1.70 m gives BMI = 70 / (1.70)^2 = 24.2, which is Normal weight; the healthy range for this height is 53.4-72.0 kg. A limitations block explains that BMI does not distinguish muscle from fat and should be combined with other measures for a complete picture.