BMI Calculator
Type your weight and height. See your BMI under both the standard WHO thresholds and the modified thresholds for Asian populations, plus the healthy weight range for your height, BMI Prime, and the Ponderal Index. Math runs in your browser — nothing you enter is uploaded.
Full WHO classification table
| Category | BMI range |
|---|---|
| Severe thinness | < 16 |
| Moderate thinness | 16 – 17 |
| Mild thinness | 17 – 18.5 |
| Normal | 18.5 – 25 |
| Overweight | 25 – 30 |
| Obese class I | 30 – 35 |
| Obese class II | 35 – 40 |
| Obese class III | ≥ 40 |
Read this before reading too much into your number
BMI is a quick screen, not a diagnosis. It can't distinguish muscle from fat, doesn't account for body composition or fat distribution, and was originally derived from 19th-century data on European adult men.
Two examples it gets wrong: an NFL linebacker at 6'2" / 250 lb has a BMI of 32 ("obese class I") with sub-10% body fat. A sedentary 5'8" / 145 lb adult has a BMI of 22 ("healthy") with 35% body fat and elevated cardiometabolic markers. The number knows nothing about either of them.
Pair BMI with waist circumference (a simple proxy for visceral fat — under 94 cm / 37 in for men, under 80 cm / 31.5 in for women is a common low-risk threshold) and your doctor's clinical judgment. The article below goes deeper on why.
Why BMI is a population statistic, not a personal diagnosis →
About the threshold systems
The WHO general thresholds (18.5 / 25 / 30) come from a 1995 WHO consultation. They were derived primarily from European-ancestry data and are the standard everywhere.
The Asian-population thresholds (18.5 / 23 / 27.5) come from the 2004 WHO Western Pacific Region report "Redefining obesity and its treatment." Multiple studies on South and East Asian populations found elevated diabetes, hypertension, and cardiovascular risk at lower BMIs than the general thresholds suggest. Several countries (Japan, India, Singapore) have adopted these as their official cutoffs.
Pick whichever system better reflects the population your health metrics are usually compared against. Or use both as bracketing data points.
Related
- Health hub — every health tool on tooljo
- Running pace calculator — for cardio training
- Unit converter — kg ↔ lb, cm ↔ inches
FAQ
Is anything I enter sent to a server?
No. The math runs in your browser via a small TypeScript module. No weight, height, or BMI data is uploaded — open DevTools → Network and confirm. We don't even ship analytics on the BMI tool.
Why two threshold systems?
The standard WHO general thresholds (18.5 / 25 / 30) were derived primarily from European populations. Subsequent research (Indian Diabetes Federation 2009, WHO Asia-Pacific guidelines 2000) found that South Asian and East Asian populations show elevated cardiometabolic risk at lower BMIs. The Asian-population thresholds (18.5 / 23 / 27.5) reflect that. If your ancestry traces to Asia, the modified thresholds may be more representative.
Is BMI a good measure of health?
It's a population statistic, not a diagnosis. BMI doesn't distinguish muscle from fat — most professional athletes are 'overweight' by BMI. It doesn't account for fat distribution (visceral vs subcutaneous fat have very different cardiometabolic risk profiles). It was originally derived from data on European adult men and may not generalize. Use it as a quick screening tool — pair with waist circumference, body composition, and your doctor's judgment for an actual assessment.
What's the formula?
Metric: BMI = weight (kg) / height (m)². Imperial: BMI = (weight (lb) / height (in)²) × 703. Same number both ways — units cancel in the ratio. The 703 factor is just the unit conversion.
How is the healthy weight range calculated?
It's the WHO 'normal' band (18.5–25 kg/m²) solved for weight at your height: low = 18.5 × height (m)² and high = 25 × height (m)². At 1.70 m that's 18.5 × 2.89 ≈ 53.5 kg to 25 × 2.89 ≈ 72.3 kg. If your entered weight falls outside the band, the tool also shows roughly how far above or below you are — a distance, not a prescription. The same caveats as BMI itself apply.
What is BMI Prime?
Your BMI divided by 25 (the upper healthy cutoff). It re-expresses BMI as a ratio: 1.00 means you're exactly at the cutoff, 0.90 means 10% below it, 1.20 means 20% above it. Same information as BMI, just easier to read as 'percent above/below the line.'
What is the Ponderal Index?
Weight divided by height cubed (kg/m³) instead of squared. Because it cubes height, it drifts less for very tall or very short adults — BMI tends to read tall people as heavier and short people as lighter than they are. Typical healthy values fall around 11–15 kg/m³. It's shown here as a cross-check, not a replacement; it has the same blind spots about body composition.
Should children use this?
No. Children and teens use age-and-sex-adjusted percentile charts, not adult BMI thresholds. Talk to a pediatrician.