BMI Calculator
Work out your Body Mass Index and see exactly where it falls on the scale, plus the healthy weight range for your height.
Related tools
Body Mass Index is a quick, rough screening number — weight relative to height — that doctors and researchers use as a population-level starting point, not a personal diagnosis. This calculator gives you the number instantly, shows exactly where it falls on the standard scale, and works out the weight range considered healthy for your specific height.
How BMI is calculated
In metric units: weight (kg) ÷ height (m)². In imperial units: 703 × weight (lb) ÷ height (in)². Both formulas measure the same thing — weight scaled against the square of height — the 703 factor just converts pounds and inches into the equivalent metric result without needing to convert units yourself.
Reading the categories
The gauge above uses the World Health Organization's standard adult ranges: under 18.5 is classed as underweight, 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight, and 30 and above as obese (which is further split clinically into Class I, II, and III as it rises). These bands were built from population health data and are a useful general marker, not a strict cutoff — someone at 24.9 and someone at 25.1 aren't meaningfully different in health terms.
What BMI doesn't tell you
BMI can't distinguish muscle from fat, which is why very muscular people — athletes, bodybuilders — are often classified as "overweight" or "obese" despite low body fat. It also doesn't account for where fat is distributed, which matters more for health risk than total weight alone, and the standard ranges weren't calibrated for children, pregnant women, or older adults, whose healthy ranges differ. Some research also suggests the standard thresholds fit some ethnic groups less well than others.
The healthy weight range
Rather than just telling you a category, this calculator also works the formula backward: it takes the "normal" BMI band (18.5–24.9) and your entered height to show the actual weight range that would land you in that band. That's often more directly useful than the BMI number itself if the goal is a concrete weight target.
Methodology & assumptions
This uses the standard adult BMI formula — weight (kg) ÷ height (m)² in metric, or 703 × weight (lb) ÷ height (in)² in imperial — the same formula used by the WHO and the CDC, with the 18.5 / 25 / 30 category cutoffs above being the standard WHO adult ranges. It doesn't adjust for age, sex, muscle mass, or frame size, which is exactly what the limitations section above covers — treat the result as a general screening number, not a diagnosis. Formula last verified: September 2026.
Frequently asked questions
Is BMI accurate for everyone?
No — it's a population-level screening tool, not an individual diagnosis. It tends to overestimate body fat in muscular people and can underestimate it in older adults who've lost muscle mass. Use it as a starting point, not a verdict.
Is my height and weight uploaded anywhere?
No. The calculation happens entirely in your browser using plain arithmetic — nothing you enter here is sent to a server or stored anywhere once you leave the page.
Does this work for children?
Not accurately — children and teens are assessed on age- and sex-specific growth charts (BMI-for-age percentiles), not the fixed adult categories this calculator uses. This tool is built for adults.
Why does the calculator show a weight range instead of just telling me to lose or gain weight?
Because a single target number is more useful than a category label, and because this tool has no basis to make a health recommendation — that range is simple arithmetic on the standard "normal" band, shown for reference, not medical advice.
What's the difference between the Overweight and Obese categories?
Overweight covers BMI 25 to 29.9, and Obese starts at 30. Obese is further split clinically into Class I (30–34.9), Class II (35–39.9), and Class III (40 and above), reflecting progressively higher associated health risk in population studies.