BMI Calculator
Body Mass Index with metric/imperial unit toggle and a full WHO category chart (underweight subtypes, normal, overweight, obese classes I–III) showing where your reading falls.
Result
- CategoryNormal weightHealthy
- Healthy weight rangeBMI 18.5–24.9 for your height56.7 kg – 76.3 kg
- Weight to reach normal (low end)✅ already in range
- Height175.0 cm
WHO BMI categories
Your reading is highlighted. WHO Technical Report Series 894 (2000).
- Severe thinnessBMI 0.0 – 15.9
- Moderate thinnessBMI 16.0 – 16.9
- Mild thinnessBMI 17.0 – 18.4
- Normal rangeYour readingBMI 18.5 – 24.9
- OverweightBMI 25.0 – 29.9
- Obese class IBMI 30.0 – 34.9
- Obese class IIBMI 35.0 – 39.9
- Obese class IIIBMI ≥ 40.0
How to use this calculator
- Pick your preferred units (metric or imperial).
- Enter your weight and height as accurately as possible.
- Read the category and the healthy weight range for your height.
About this tool
Body Mass Index (BMI) is a simple, widely used screening tool that estimates body fat from weight and height. Switch between metric (kg, cm) and imperial (lb, in) units; the underlying math is identical. The WHO categories — underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), obese (≥30) — apply to most adults but have known limitations. The chart below the result expands those four bands into the full WHO classification (severe/moderate/mild thinness and obese classes I–III) and highlights the row your reading lands in. BMI doesn't distinguish muscle from fat, so very athletic people may register "overweight" without being unhealthy. It also doesn't account for fat distribution, ethnicity, or age. Treat your BMI as a starting point for a conversation with a healthcare provider, not a diagnosis.
What this calculator does
This calculator returns your Body Mass Index — a single number that compares your weight against your height — and maps it to the World Health Organization's four-band classification: underweight, normal, overweight, or obese. It also reports the healthy weight range for your height (BMI 18.5 to 24.9) and how many kilos you would need to lose or gain to move into that band. Both metric and imperial units are supported, and the underlying math is identical to the formulas used by the CDC and NIH.
How it works — the formula
BMI = weight (kg) ÷ height (m)²Body Mass Index expresses weight as a function of height squared so the same person reads similarly tall or short. The WHO classifies adults into four bands: under 18.5 (underweight), 18.5–24.9 (normal), 25.0–29.9 (overweight), and 30.0+ (obese). Imperial users multiply weight in pounds by 703 and divide by height in inches squared, which is mathematically identical.
Worked examples
- Inputs:
- weight = 70 kg, height = 175 cm
- Output:
- BMI = 22.86 → Normal weight
Sits comfortably in the middle of the 18.5–24.9 healthy band, so no clinical concern from BMI alone.
- Inputs:
- weight = 75 kg, height = 165 cm
- Output:
- BMI = 27.55 → Overweight
About 7 kg above the upper edge of the healthy band. The WHO flags 25–29.9 as a screening risk, not a diagnosis.
- Inputs:
- weight = 180 lb, height = 70 in
- Output:
- BMI = 25.83 → Overweight
Demonstrates the lb·703 / in² shortcut. The result matches metric output within rounding (≤ 0.01 BMI).
When to use this vs other tools
BMI is a quick screen, not a body-composition assessment. Reach for one of the related tools when you need a more specific answer.
- Ideal Weight Calculator
Use when you want a target weight range, not a category. Combines the WHO healthy-BMI band with the Devine / Robinson / Miller / Hamwi formulas (heights ≥ 152 cm).
- Body Fat Calculator
Use when BMI flags you as overweight but you carry significant muscle mass — body-fat percentage separates lean tissue from adipose tissue, which BMI cannot do.
- Waist-Hip Ratio
Use to assess cardiovascular risk from fat distribution. Visceral (abdominal) fat is more strongly linked to disease risk than equivalent fat on hips or thighs — a measure BMI ignores entirely.
- Calorie Calculator (TDEE)
Use once you have a target weight from BMI / ideal-weight to set the daily calorie intake needed to reach and hold it.
Authority note
The WHO report is the standard reference for the adult BMI thresholds used worldwide (18.5, 25, 30). CDC and NIH publish their own adult BMI calculators that use these same WHO cutoffs.
Limitations
- Does not distinguish lean muscle from fat — competitive athletes routinely score "overweight" without elevated health risk.
- Ignores fat distribution: visceral (abdominal) fat carries more cardiovascular risk than equivalent fat on hips or thighs.
- Not validated for children, pregnant or breastfeeding women, or people with significant edema or limb amputation.
- WHO cutoffs are calibrated to European populations; some health authorities use lower thresholds for South Asian, East Asian, and Pacific Islander populations.
BMI is a screening tool, not a diagnosis. This calculator does not provide medical advice — consult a healthcare professional before making decisions about weight, diet, or exercise based on your reading.