Calculate your BMI
Enter your height and weight. Everything is computed instantly in your browser.
BMI categories (WHO)
The World Health Organization classifies adult BMI into six bands. These cutoffs are the same for men and women aged 20 and over.
| BMI | Category | What it signals |
|---|---|---|
| Below 18.5 | Underweight | May indicate undernutrition or an underlying condition worth checking. |
| 18.5 – 24.9 | Healthy weight | Associated with the lowest risk of weight-related disease for most adults. |
| 25.0 – 29.9 | Overweight | Risk starts rising; a good moment for lifestyle review. |
| 30.0 – 34.9 | Obese — Class I | Elevated risk of type 2 diabetes, hypertension and heart disease. |
| 35.0 – 39.9 | Obese — Class II | High risk; professional guidance is strongly advised. |
| 40.0 and above | Obese — Class III | Very high risk; medical supervision recommended. |
Some public-health agencies suggest lower action cutoffs for Asian populations (overweight from 23, obesity from 27.5), because metabolic risk rises earlier. See the limitations section below.
How BMI is calculated
One formula, two unit systems. BMI is your weight divided by the square of your height.
Worked examples
Example 1 — Metric
A person is 180 cm tall and weighs 80 kg.
= 80 ÷ 3.24
= 24.69
BMI 24.69 → Healthy weight ✓
Healthy range for 180 cm: 59.9 – 80.7 kg.
Example 2 — Imperial
A person is 5'10" tall and weighs 180 lb.
= 126,540 ÷ 4,900
= 25.82
BMI 25.82 → Overweight
Healthy range for 5'10": 128.9 – 173.6 lb — about 6.4 lb above it.
Example 3 — Healthy range
A person is 165 cm tall. What weight is "healthy"?
high: 24.9 × 1.65² = 67.8 kg
Healthy weight: 50.4 – 67.8 kg
Anyone at this height inside that window has a BMI of 18.5 – 24.9.
Ponderal Index (Corpulence Index)
BMI divides by height squared, which slightly favors tall people. The Ponderal Index divides by height cubed, so it compares body "stockiness" more fairly across heights.
For example, our 180 cm / 80 kg example has a PI of 13.72 — comfortably inside the typical range — while the 175 cm / 110 kg example scores 20.52. The Ponderal Index is far less known than BMI and has no official WHO cutoffs, so treat it as extra context, not a verdict.
When BMI gets it wrong
BMI was designed in the 1830s by Adolphe Quetelet as a population-level tool — never as a personal health diagnosis. It measures size, not health.
🏋️ Athletes & muscular builds
Muscle is denser than fat. A muscular person can land in "overweight" or even "obese" with low body fat and excellent metabolic health. BMI cannot tell the two apart.
👴 Older adults (65+)
With age, muscle is gradually replaced by fat at the same weight. Research suggests slightly higher BMI may even be protective in older adults — cutoffs should be interpreted with a doctor.
🤰 Pregnancy
BMI is not meant for pregnant people at all. Weight gain during pregnancy follows its own medical guidelines — never judge it by standard BMI bands.
🧬 Ethnicity differences
At the same BMI, Asian populations tend to carry more body fat and face higher diabetes risk earlier. WHO flags overweight from 23 and obesity from 27.5 as action points for Asian adults.
📍 Where fat sits matters
Two people with BMI 27 can have very different risk: fat around the abdomen (visceral fat) drives heart disease and diabetes far more than fat on hips and thighs. Waist measurement adds what BMI misses.
🧒 Children & teens
For ages 2–19, doctors use BMI-for-age percentiles (CDC/WHO growth charts), not adult cutoffs — because healthy BMI shifts as kids grow. This calculator's categories are for adults 20+.
BMI only tells part of the story
This tool calculates BMI only. For a fuller picture of body composition — what share of your weight is actually fat — try our body fat calculator (Navy, YMCA and other methods compared).
Planning to change your weight? Find out how many calories your body actually needs with our TDEE calculator.
BMI — frequently asked questions
What is a good BMI?
For most adults, a "good" or healthy BMI is 18.5 to 24.9. This is the WHO's healthy-weight band and is associated with the lowest risk of weight-related disease. A BMI of 25 to 29.9 is classified as overweight, and 30 or above as obese — but these are screening bands, not a personal diagnosis.
How do I calculate my BMI manually?
In metric: divide your weight in kilograms by your height in meters squared — BMI = kg ÷ m². For example, 80 kg ÷ (1.8 × 1.8) = 24.69. In imperial: multiply your weight in pounds by 703, then divide by your height in inches squared — BMI = 703 × lb ÷ in². The calculator above does both instantly.
What are the BMI categories and ranges?
The WHO defines six adult bands: underweight (below 18.5), healthy weight (18.5–24.9), overweight (25–29.9), obese class I (30–34.9), obese class II (35–39.9), and obese class III (40 and above). The same cutoffs apply to men and women aged 20 and over.
Is BMI accurate?
BMI is accurate at what it actually measures — weight relative to height — and it works as a population screening tool. But it is not accurate as a personal health verdict: it cannot distinguish muscle from fat, ignores where fat is stored, and misclassifies muscular people, many older adults, and pregnant women. Use it as one data point alongside waist measurement, activity, and blood markers.
My BMI says overweight but I'm muscular. Why?
Because muscle is denser than fat, a muscular person weighs more at the same size — and BMI only sees weight and height. Strength athletes are routinely classified as "overweight" or even "obese" despite low body fat and good metabolic health. If you lift regularly, body fat percentage is a far better metric for you.
What is a healthy weight for my height?
Multiply the healthy BMI band (18.5–24.9) by your height squared. For example, at 170 cm: 18.5 × 1.7² = 53.5 kg at the low end and 24.9 × 1.7² = 72.0 kg at the high end. The calculator above shows your personal healthy weight range automatically with every result.
How can I lower my BMI?
BMI falls when weight falls relative to height, so the levers are the familiar ones: a modest sustained calorie deficit, more daily movement, strength training to preserve muscle, better sleep, and less alcohol and sugary drinks. Aim for gradual change — around 0.5 kg per week — and consider our TDEE calculator to find a sensible calorie target. If your BMI is 30+, involve a health professional.
Is BMI different for men and women?
The formula and the WHO cutoffs are identical for men and women. In practice, women typically carry a higher body fat percentage than men at the same BMI, which is one more reason BMI alone can't describe body composition. There is no separate "BMI calculator for men" or "for women" — one calculator serves both.
Can children and teenagers use this BMI calculator?
The math works, but the adult categories do not apply under age 20. Doctors assess kids and teens with BMI-for-age percentiles from CDC or WHO growth charts, because a healthy BMI shifts as children grow. If you entered an age under 20 above, treat the category label with caution and ask a pediatrician for a proper assessment.
What is BMI Prime?
BMI Prime is simply your BMI divided by 25 (the upper limit of healthy). A BMI Prime below 1.0 means you're under the overweight threshold; 1.0 is exactly the boundary; above 1.0 you're over it. It's just a compact way to express how far you are from the healthy band — for example, BMI 30 gives a BMI Prime of 1.20.
What is the Ponderal Index?
The Ponderal Index (also called the Corpulence Index) is weight in kilograms divided by height in meters cubed (kg ÷ m³). Unlike BMI, which slightly favors tall people, it compares "stockiness" fairly across heights. A typical adult reference range is about 11 to 14. It has no official WHO cutoffs, so use it as extra context rather than a verdict.
Does age affect BMI interpretation?
The formula doesn't change with age, but the interpretation should. After about 65, gradual muscle loss means the same BMI can hide more fat, yet research also suggests slightly higher BMI may be protective in older adults. There are no official separate cutoffs for seniors — if you're over 65, discuss your result with your doctor rather than chasing the 18.5–24.9 band alone.
Which is better: BMI or body fat percentage?
Body fat percentage is the better individual metric because it separates fat from muscle — exactly what BMI cannot do. BMI wins on convenience: it needs only height and weight. The honest answer is to use both: BMI for quick screening, body fat percentage (via Navy tape method, calipers, or a scan) for the real picture. Our body fat calculator compares the common estimation methods side by side.
Is a BMI of 25 overweight? What BMI counts as obese?
Yes — 25.0 is the exact start of the overweight band (25.0–29.9). Obesity starts at 30.0, split into class I (30–34.9), class II (35–39.9), and class III (40+). Note the boundary is sharp on paper but risk rises gradually in reality: 24.9 and 25.1 are barely different physiologically.
Who invented BMI?
Belgian mathematician Adolphe Quetelet devised the formula in the 1830s as the "Quetelet Index" for studying populations — not individuals. It was renamed Body Mass Index in the 1970s when researcher Ancel Keys popularized it. Its origin as a population statistics tool is exactly why it struggles as a personal health measure.
Does this calculator store or send my data?
No. This is a static page: every calculation happens locally in your browser with JavaScript, and nothing is transmitted anywhere. There is no account, no analytics on your inputs, and closing the tab erases everything. And remember: BMI is a screening tool, not a diagnosis — consult a qualified health professional about any health decisions.