BMI Calculator
Type your height and weight and the calculator returns your BMI (kilograms per square metre) along with the World Health Organization adult category: underweight, normal weight, overweight, or obesity. It also shows BMI Prime and the weight range that would land you in the normal band for your height, so you can see the gap in concrete kilos or pounds — useful for a baseline, not a diagnosis.
How BMI is calculated
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1
Enter height and weight
Switch between metric (cm / kg) and imperial (in / lb). For imperial mode, enter height as total inches.
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2
Formula is applied
BMI = weight (kg) / height (m)^2. Imperial is converted internally; the output BMI is always in kg/m².
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3
Category is looked up
The main result uses adult WHO cut-offs at 18.5, 25 and 30; the reference table below also breaks obesity into classes at 35 and 40.
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4
Healthy-weight range appears
For your specific height, the calculator shows what you would weigh at BMI 18.5 and BMI 24.9 — your "normal" window.
WHO adult BMI categories
| BMI (kg/m²) | Category |
|---|---|
| < 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class I |
| 35.0 – 39.9 | Obesity class II |
| ≥ 40.0 | Obesity class III |
Asian-population guidelines (IOTF, WHO Asia Pacific) use lower thresholds — 23 for overweight, 27.5 for obesity — because body fat percentages tend to run higher at any given BMI.
The result panel keeps the main category on the standard adult WHO bands, then adds BMI Prime (BMI ÷ 25) and the height-specific 18.5–24.9 healthy-weight range. Those extra numbers make the result easier to compare without turning BMI into a diagnosis.
Where BMI falls short
- Muscle mass: athletes and lifters often test “overweight” by BMI despite low body fat. Rugby forwards and bodybuilders routinely land in the 28-32 range.
- Age and sarcopenia: older adults lose muscle, so a “normal” BMI can mask under-muscled frames.
- Body composition: BMI says nothing about where fat is distributed. Abdominal (visceral) fat is a bigger cardiometabolic risk than hip/thigh fat at the same BMI.
- Pregnancy: BMI is not meaningful during pregnancy or the first few months postpartum.
Better companion measures
- Waist-to-height ratio: keep waist < half your height.
- Body fat percentage: via DEXA, hydrostatic weighing or a good bioimpedance scale.
- Waist circumference: > 102 cm (40 in) for men and > 88 cm (35 in) for women flags elevated risk regardless of BMI.
Frequently Asked Questions
It’s a population-level screening tool, not a diagnosis. Muscular, pregnant, very tall/short, elderly and some ethnic groups routinely get misclassified. Use it as one data point among several.
Asian populations show elevated metabolic risk at lower BMI values, so WHO Asia Pacific sets overweight at 23 and obesity at 27.5. This calculator keeps the main result on standard adult WHO bands and lists the Asia-Pacific thresholds as context.
Only with age- and sex-specific percentile charts — adult categories do not apply. The calculator is for adults 18 and older; use a paediatric BMI-for-age tool for children.
The span from BMI 18.5 to 24.9 is what WHO calls normal. For your height, the calculator prints that as a specific kg or lb window, and the lower half often maps to better long-term cardiovascular markers.
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