The BMI Calculator computes your Body Mass Index in metric or imperial units with instant WHO category classification, healthy weight range for your height, and waist circumference risk thresholds. Includes waist-to-height ratio guidance — often a better metabolic risk predictor than BMI alone.
24.2
kg/m²
0
53.5
kg
72
kg
-16.5
kg
2
kg
24.2
kg/m²
0
53.5
kg
72
kg
-16.5
kg
2
kg
BMI has been the universal medical shorthand for weight classification for decades, but there's growing evidence that waist circumference and waist-to-height ratio predict metabolic risk more accurately — especially for the 20–30% of people who are "normal weight obese" (normal BMI, high body fat) or "metabolically healthy obese" (high BMI, normal metabolic markers). The BMI calculator gives you your BMI and weight category, plus guidance on the additional measurements worth tracking. Always discuss your results with your healthcare provider.
Metric: BMI = weight_kg / height_m²
Imperial: BMI = (weight_lbs / height_in²) × 703
WHO adult classification: Underweight below 18.5 | Normal 18.5–24.9 | Overweight 25.0–29.9 | Obese I 30.0–34.9 | Obese II 35.0–39.9 | Obese III 40.0+
For a 175 cm / 5'9" person: ideal weight range (BMI 18.5–24.9) = 56.6–76.2 kg (125–168 lbs). Use this online calculator for your own measurements. The BMR calculator tells you how many calories your body burns at rest at your current weight.
Visceral adipose tissue — the fat stored around abdominal organs — is metabolically active in ways subcutaneous fat (under the skin) is not. It releases inflammatory cytokines, contributes to insulin resistance, and directly increases cardiovascular risk. Waist circumference is the simplest proxy for visceral fat. Thresholds associated with increased metabolic risk:
A person with normal BMI but waist circumference above threshold has "normal weight central obesity" — metabolic risk despite normal BMI. This affects an estimated 24% of normal-BMI adults.
Waist-to-height ratio (WtHR) = waist circumference / height (both in same units). Below 0.5 is the universal "keep your waist to less than half your height" target — this boundary applies across ages, sexes, and ethnicities with consistent predictive validity for metabolic risk, making it more universally applicable than sex-specific waist cutoffs. A WtHR of 0.5–0.59 indicates increased risk; 0.6+ indicates high risk. For a 5'10" (178 cm) person: keep waist under 89 cm (35 inches).
The body fat percentage calculator and health measurement calculators provide complementary body composition tools.
The relationship between BMI and health outcomes changes with age. For older adults (65+): the "normal" BMI range associated with best survival outcomes shifts upward to approximately 22–27. Being underweight carries greater mortality risk in older adults than overweight — this is called the "obesity paradox" and likely reflects that higher BMI in older adults provides nutritional reserve during illness and protects against bone loss and frailty. Muscle mass (which contributes to BMI without adding metabolic risk) declines with age, so an older adult at BMI 22 may have proportionally more fat than a younger adult at the same BMI. Pediatric BMI uses age- and sex-specific percentiles entirely — adult cutoffs don't apply.
A BMI below 18.5 indicates underweight status and may signal nutritional deficiency. BMI between 18.5 and 24.9 is considered normal and is associated with the lowest health risks. BMI from 25.0 to 29.9 is classified as overweight, and 30.0 or above indicates obesity. The healthy weight range shown gives you a target window. Remember that BMI does not distinguish between muscle and fat mass, so use it alongside other measurements for a complete picture.
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A 70 kg person at 175 cm has a BMI of 22.9, well within the normal range.
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At 95 kg and 170 cm, BMI is 32.9 indicating Obese Class I. Healthy range is 53.5-71.9 kg.
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