Free Online BMI Calculator.
Enter your age, gender, height, and weight to see your BMI, category, estimated body-fat percentage, healthy weight range, and daily calorie maintenance — using WHO and CDC standards.
Awaiting input.
BMI is a screening tool — it doesn't measure body fat directly and can over- or under-estimate adiposity for athletes, the elderly, or some populations. Read the caveats →
Saved results (this device)
| Date | BMI | Category | Weight | Healthy range |
|---|
How to use this free online BMI calculator.
Our free BMI calculator online turns four numbers — age, gender, height and weight — into a Body Mass Index, a category label (underweight, normal, overweight or obese), and a dozen useful follow-on numbers: BMI Prime, Ponderal Index, body-fat percentage, healthy weight range, ideal weight, lean body mass, BMR, daily calorie maintenance and waist-to-height risk. The whole thing happens in your browser. There is no account, no upload, and your numbers never leave the page.
1. Pick the units that match how you weigh yourself
The toggle at the top of the form switches between metric (kg / cm), imperial (lb / ft + in), kg + feet/inches, and lb + inches. The math is identical underneath — Body Mass Index is defined in kilograms per square metre, and we silently convert imperial inputs for you. If you change units after typing, the calculator carries your values across the swap so you do not have to re-type. This handles the common queries "bmi calculator kg", "bmi calculator in kg and cm", "bmi calculator lbs", and "bmi calculator ft and in".
2. Choose the right age group
For adults (age 20+) we apply the WHO BMI cut-offs: under 18.5 is underweight, 18.5–24.9 is the healthy band, 25–29.9 is overweight, and 30 and over is obesity. For children and teenagers (age 2–19) BMI works differently — what matters is the percentile against same-age, same-sex peers. Switch to Child / Teen mode and the calculator labels your BMI against CDC reference bands instead of the adult thresholds. For an exact CDC percentile (which depends on a sex-and-age lookup table), see the chart on the BMI Charts page. If your population has lower cardiometabolic thresholds, switch on Asian BMI (overweight ≥ 23, obese ≥ 27.5).
3. Enter age, gender, height and weight
Type your age in years and pick male or female from the dropdown. Then enter height and weight. The calculator recomputes on every keystroke, so you do not have to press a button — the gauge animates to your BMI as you type. You can still hit Calculate if you prefer; the result is identical. Use Reset to clear everything and start again. Optionally, open Optional: add waist circumference and the calculator will also show your waist-to-height risk.
4. Read the BMI value, the gauge and the category
The big number is your BMI rounded to one decimal place. The half-pie gauge above it shows the four WHO bands in colour — blue for underweight, green for healthy, amber for overweight, red for obesity — with a needle pointing at your number. Underneath, the pill chip names the band you fall into, and a short sentence tells you what that means in plain language. BMI Prime (your BMI divided by 25) tells you how far you are from the upper edge of the healthy band — 1.00 is the threshold, 0.74 is the middle of the band.
5. Use the body-fat, healthy-weight, ideal weight and calorie panels
BMI alone is a blunt tool, so the calculator also estimates:
- Body fat percentage using the Deurenberg formula
(
1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4). This is an estimate, not a measurement, and is suppressed under age 18 because the formula was derived on adults. - Healthy weight range for your height, derived by solving the BMI formula against the WHO band 18.5–24.9.
- Ideal weight using the Devine formula (50 kg male / 45.5 kg female + 2.3 kg per inch over 5 ft), and Lean Body Mass using the Boer formula.
- BMR (Mifflin–St Jeor) and TDEE at five activity levels (sedentary 1.2 → very active 1.9).
- Waist-to-height ratio with a risk label when you provide waist circumference.
6. Save, share, copy or download the result
When you have a result, use Save to history to keep the last 20 entries on this device (browser only — nothing is uploaded), Share to copy a URL that pre-fills the form, Copy result to drop a one-line summary into your clipboard, or Download CSV / PDF for a richer record. CSV gives you the raw numbers for spreadsheets; PDF uses your browser's print dialog to produce a one-page summary you can save, email or take to a clinician.
What if I get an unusual result?
BMI does not distinguish muscle from fat, water from bone, or how weight is distributed. Heavily-muscled athletes can read as "overweight" on BMI without carrying excess fat, and older adults can read as "healthy" on BMI while having low muscle mass. The WHO also notes that for many Asian populations the risk threshold for type 2 diabetes and cardiovascular disease starts lower — around BMI ≥ 23 for overweight and ≥ 27.5 for obesity. For anything decision-shaped, take the number to a clinician rather than acting on it alone.
What is BMI?
Body Mass Index is a screening number first proposed
by the Belgian polymath Adolphe Quetelet in the 19th century and
adopted by the World Health Organization as a population-level
indicator of weight relative to height. The BMI formula is
weight (kg) / height (m)², or equivalently
703 × weight (lb) / height (in)². It is cheap, fast and
reproducible, which is why every health system on Earth uses it as a
starting point — but it is a screen, not a diagnosis.
For a deeper dive on the history, formula derivation, the difference between adult and child interpretation, the Asian-cohort adjustments and the known limitations, see our About BMI page. The Charts page has the full WHO adult tables and the CDC percentile growth references in printable form.
Pair your BMI with these calculators
Deurenberg estimate of body-fat percentage from BMI, age and sex.
Devine, Robinson and Miller formulas for your target weight.
Boer formula for fat-free mass at your height and weight.
Mifflin–St Jeor basal metabolic rate — calories you burn at rest.
Total daily energy expenditure (TDEE) with five activity levels.
The exact calorie target that holds your weight steady.
Reviewed by certified professionals.
Every long-form article on this site is reviewed by a certified physiotherapist, registered dietitian, or physician whose area of practice matches the topic — never a faceless byline. Each reviewer is named, credentialed, contactable, and independent of the site.