Enter your height and weight in either metric or imperial units and this BMI calculator shows your body mass index, the WHO weight category it falls in, the healthy weight range for your exact height, and your BMI prime. Switching units converts the numbers you already typed, and an optional toggle applies the lower cut-offs a WHO expert panel recommends for people of Asian descent. For children and teens it shows the raw BMI and explains why a growth-chart percentile is needed instead of the adult categories.
BMI is a screening number, not a verdict on your health, so read it alongside the limitations explained under the result. If you want to act on it, the calorie calculator estimates your daily energy needs and a safe deficit or surplus. To convert other measurements, use the unit converter, and the percentage calculator helps you track change over time. Everything runs in your browser — nothing you enter is sent anywhere.
Wondering how much weight to put on the number? Read what BMI can and can't tell you — where the cut-points come from, what BMI misses (muscle, age, fat distribution), why children use percentiles, and the measures clinicians pair it with.
Frequently asked questions
How is BMI calculated?
Body mass index is your weight in kilograms divided by your height in meters squared: BMI = kg ÷ m². At 175 cm and 70 kg that is 70 ÷ 1.75² = 22.9. In imperial units the same formula becomes 703 × pounds ÷ inches², which is what the CDC publishes. This calculator converts imperial entries to metric internally, so both modes give the same number, and it keeps full precision until the final one-decimal display. The category is assigned from that displayed value, so a BMI shown as 25.0 is always labeled overweight.
What BMI range is considered healthy?
For adults the World Health Organization classes a BMI below 18.5 as underweight, 18.5 to 24.9 as a healthy weight, 25 to 29.9 as overweight, and 30 or more as obesity, split into class I (30 to 34.9), class II (35 to 39.9), and class III (40 and above). The calculator also turns the healthy band into a weight range for your exact height, so you can see how far, if at all, you are from it in kilograms or pounds. Being inside the range is a screening result, not proof of good health.
Why is there an option for Asian cut-offs?
A 2004 WHO expert consultation found that many Asian populations develop type 2 diabetes and heart disease at lower BMIs than European populations. It suggested public-health action points of 23 (increased risk) and 27.5 (high risk), and health agencies such as Singapore's Health Promotion Board use them for adults. Turning on the toggle switches the categories, the healthy weight range, and BMI prime to those lower cut-offs. It is a population guideline, not a personal diagnosis, so discuss it with your doctor if you are near a boundary.
Can I use this BMI calculator for children and teens?
Yes, with a caveat. The raw BMI formula is the same, but for ages 2 to 19 the CDC interprets it with BMI-for-age percentiles, because normal body fat changes as children grow and differs between boys and girls. In child/teen mode the calculator shows the BMI only and does not invent a percentile. Plot the number on the CDC growth chart for the child's sex and age, or ask a pediatrician, to see where it falls. Adult categories should never be applied to a child.
What is BMI prime?
BMI prime is your BMI divided by the upper limit of the healthy range, which is 25 on the standard scale (23 with the Asian cut-offs). A value of 1.00 means you are exactly at the top of the healthy range; 0.90 means 10 percent below it; 1.20 means 20 percent above it. Because it is a simple ratio, it makes it easy to see how far from the boundary you are without memorizing category thresholds. Values below 0.74 (18.5 ÷ 25) indicate underweight.
Is BMI accurate for athletes and older adults?
Not always. BMI only uses height and weight, so it cannot tell muscle from fat. A muscular athlete can be classed as overweight while carrying little body fat, and an older adult who has lost muscle can land in the healthy range while carrying more fat than the number suggests. It also does not apply during pregnancy. BMI works well as a quick population screen; waist measurement, body-fat testing, and a clinician's judgment fill in what it misses. Treat a surprising result as a prompt for a conversation, not a conclusion.