BMI Calculator

Related guide

BMI, Age and Date Calculators: Which Numbers to Trust, and When
The BMI page classifies the rounded number, not the real one. The age page anchors its counters to UTC midnight and keeps ticking after you clear the box. The date page counts days from local midnight, so a clock change can cost you one. Every figure below was measured on the pages themselves.

What BMI is, and what it is not

Body Mass Index is a single ratio between your weight and the square of your height. It is a screening number: it was designed to describe populations, not to diagnose an individual, and it cannot tell muscle from fat, cannot see where fat is stored, and is not adjusted for age, sex or pregnancy.

That is why two people with the same BMI can be in very different health situations — a trained athlete and a sedentary person of the same height can both read 27. Treat the number as a starting point for a conversation, not a verdict.

The formula this calculator uses

In metric mode: BMI = weight in kilograms ÷ (height in metres)². At 170 cm and 65 kg that is 65 ÷ 1.7² = 22.5.

In imperial mode the inputs are converted first — inches × 0.0254 to metres, pounds × 0.453592 to kilograms — and the same formula is applied. That is mathematically identical to the 703 × lb ÷ in² shortcut, so both modes give the same answer for equivalent values.

The result is rounded to one decimal place, and the marker on the scale below shows where that value sits among the categories.

Which cut-offs the categories use

This calculator uses 18.5, 24 and 28 as its boundaries: under 18.5 is underweight, 18.5–24 is normal, 24–28 is overweight, and 28 or above is obese. Those are the cut-offs adopted for Asian populations.

The WHO international cut-offs are 25 and 30. Neither set is wrong — they are calibrated for different populations — but it does mean this page can flag "overweight" at a BMI where another calculator still says "normal". If you are comparing tools, check which thresholds each one uses before worrying about the difference.

FAQ

Is BMI accurate for athletes or bodybuilders?
Not very. Muscle is denser than fat, so a muscular person can register a high BMI with a low body-fat percentage. A waist measurement or a body-fat estimate is far more informative in that case.

Do metric and imperial mode give the same result?
Yes, provided you enter equivalent values. The conversion factors are the exact defined ones (1 inch = 0.0254 m, 1 pound = 0.453592 kg), and both modes then run the same metric formula. Small differences you see elsewhere usually come from rounding the converted inputs.

Which thresholds does this calculator use?
Underweight below 18.5, normal 18.5–24, overweight 24–28, obese 28 and above. These are the cut-offs used for Asian populations; the WHO international cut-offs are 25 and 30.

Can I use it for children, teenagers or pregnant women?
No. Children and teenagers are assessed with age- and sex-specific percentile charts rather than fixed thresholds, and BMI is not interpreted the same way during pregnancy. Ask a clinician for those cases.

Why is my BMI the same as last year even though I gained weight?
Because BMI only responds to weight relative to height. A 5 kg gain at 170 cm moves BMI by about 1.7 points; a change in body composition at the same weight does not move it at all.

Is my height and weight stored?
No. The calculation happens locally in your browser and nothing is uploaded or saved. Reload the page and the defaults are restored.