BMI & Waist-to-Height Ratio Calculator
Calculate your body mass index and waist-to-height ratio in one calculator. Two metrics together give a significantly more accurate picture of health risks than BMI alone.
Measure horizontally at the level of the navel, standing relaxed on bare skin. Use a non-elastic measuring tape.
What is BMI (Body Mass Index)?
BMI (Body Mass Index) is the ratio of weight to height, calculated by dividing weight (kg) by the square of height (m²). It is the world's most widely used tool for assessing overweight and underweight at the population level. According to WHO classification, a normal BMI is 18.5–24.9.
BMI's biggest weakness is that it does not distinguish between muscle and fat. A strength athlete weighing 95 kg but with only 12% body fat gets the same BMI as an inactive person with 30% body fat. That's why more accurate metrics are needed alongside BMI — such as the waist-to-height ratio.
Waist-to-Height Ratio (WHtR) – better than BMI alone
The waist-to-height ratio (WHtR) is calculated by dividing waist circumference by height. The simple rule is: your waist should be less than half your height. For a person 180 cm tall, that means a waist under 90 cm.
Research shows that WHtR predicts cardiovascular disease risk, type 2 diabetes, and overall mortality better than BMI. This is because WHtR specifically measures central obesity — the most dangerous type of fat — while BMI only reflects total weight relative to height.
WHtR categories
Very slim
Health risk: Possibly underweight
Slim
Health risk: Low
Healthy
Health risk: Low – target range
Slight risk
Health risk: Slightly elevated
Elevated risk
Health risk: Elevated
High risk
Health risk: Significant
Why is central obesity dangerous?
Not all fat is the same. Subcutaneous fat (for example in the thighs and arms) is relatively harmless. Visceral fat — fat that accumulates around the internal organs in the abdominal cavity — is metabolically active and causes chronic inflammation.
Central obesity increases risk of
- •Type 2 diabetes (3–5× risk)
- •Cardiovascular disease
- •Metabolic syndrome
- •Certain cancers (colon, breast)
- •Fatty liver and insulin resistance
How to reduce belly fat
- Moderate calorie deficit (300–500 kcal/day)
- Regular exercise, especially strength training
- Adequate sleep (7–9 h) – cortisol accumulates belly fat
- Stress management
- Reducing alcohol intake
Four situations where BMI is misleading
Muscular person
BMI: High (27–30) · WHtR: Low (< 0.50)
Healthy. High BMI is due to muscle mass, not fat. WHtR reveals the true situation.
"Skinny fat" – normal weight, high fat
BMI: Normal (20–24) · WHtR: High (> 0.50)
Elevated risk. BMI looks good, but central obesity increases health risks. The most common "hidden" risk group.
Older adult
BMI: Normal · WHtR: Varies
As we age, muscle mass decreases and fat increases. BMI can stay the same even as body composition changes unfavorably.
Very tall or very short person
BMI: Inaccurate · WHtR: More accurate
BMI overestimates fatness in short people and underestimates it in tall people. WHtR works the same way for all heights.
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