BMI Calculator
Calculate your body mass index from height and weight — metric or imperial — and see the healthy weight range for your height.
How BMI works
Body mass index is weight divided by height squared: kg / m² in metric, or 703 × lb / in² in imperial. It was designed as a quick, population-level screening tool, not a diagnostic measurement of body fat — it doesn't distinguish muscle from fat, doesn't account for where fat is distributed, and its healthy ranges are based on adult data, so it applies differently across ages, sexes, and body types. The healthy weight range shown above is simply the weight that would put your BMI between 18.5 and 24.9 at your entered height.
BMI categories (WHO classification)
Your row is highlighted automatically after you calculate. "General health risk" reflects the broad population-level association used in the WHO classification — it is not a personal risk assessment, since factors like muscle mass, age, fat distribution and overall fitness all affect real health risk independently of BMI.
| BMI | Category | General health risk |
|---|---|---|
| Below 16.0 | Severe thinness | Increased |
| 16.0 – 16.9 | Moderate thinness | Increased |
| 17.0 – 18.4 | Mild thinness | Increased |
| 18.5 – 24.9 | Normal weight | Least |
| 25.0 – 29.9 | Overweight | Increased |
| 30.0 – 34.9 | Obese class I | Moderate |
| 35.0 – 39.9 | Obese class II | Severe |
| 40.0 and above | Obese class III | Very severe |
Source: WHO BMI classification, consistent with the CDC's adult BMI categories.
Limitations, and BMI for children or teens
BMI is a starting point, not a verdict. Athletes and anyone with above-average muscle mass often score "overweight" or "obese" while carrying low body fat, since muscle weighs more than fat at the same volume. Older adults can have a "normal" BMI while carrying less muscle and more fat than the number suggests. Pregnancy changes weight in ways this formula isn't designed for. And this calculator's thresholds are the adult WHO categories — they don't apply to children or teenagers, whose healthy BMI depends on age and sex and is judged against growth-chart percentiles (like the CDC's BMI-for-age charts) rather than the fixed adult bands above. If you're calculating for someone under 20, use an age-appropriate percentile calculator instead, or ask a pediatrician.
Frequently asked questions
Is BMI accurate for everyone?
No. BMI is a population-level screening number, not a diagnosis — it can't tell muscle from fat, so athletes often score "overweight" while being lean, and it applies differently to children, pregnant women and the elderly. Treat it as a starting point and talk to a doctor about what's healthy for you.
Is my data stored anywhere?
No. The calculation runs entirely in your browser; nothing you enter is uploaded.
What BMI should I aim for?
For most adults, 18.5–24.9 is considered the healthy range, but individual targets vary with age, build and health conditions.
Why does the table show "general health risk" instead of my personal risk?
Because BMI alone can't measure that. The risk labels come from population studies correlating BMI with health outcomes on average — your actual risk also depends on muscle mass, fat distribution, fitness, genetics and other conditions, which is why doctors use BMI as one input among several, not a standalone diagnosis.
Last updated: 2026-07-22