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BMI Calculator

Enter your height and weight to see your Body Mass Index and exactly where it sits on the scale. Then read the part most calculators leave out — what BMI cannot see.

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BMI scale from 14 to 40 with your result marked Under Healthy Over 30 and above 14 18.5 25 30 40 —
Your BMI plotted on the World Health Organization adult scale. The boundaries are the same for men and women.

What BMI actually measures

BMI is your weight divided by the square of your height — nothing more. It was designed in the 1830s to describe populations, not to diagnose individuals, and it is still used because it is cheap, consistent, and needs only a scale and a tape measure.

That simplicity is also its blind spot. The formula has no way of knowing what your weight is made of, or where it sits on your body. Two people can share a BMI and be in completely different health situations:

Two people with identical BMI of 27 but different body composition BMI 27 Lifts three times a week Body fat ≈ 18% Normal blood pressure, normal blood sugar. BMI 27 Mostly desk-based Body fat ≈ 34% Raised blood pressure, raised fasting glucose. Identical BMI. The formula cannot tell these two apart.
Illustrative example. Body-fat percentages shown are typical of each pattern, not measured values — the point is that BMI returns the same number for both.
If your BMI reads "overweight" and you train regularly, the number is probably describing your muscle. That is the single most common false positive in the whole scale.

The measurement that fills the gap

Waist-to-height ratio catches what BMI misses, because it measures abdominal fat specifically — the fat that sits around your organs and drives metabolic risk. It takes one tape measure and one division.

Waist-to-height ratio: divide waist by height, aim below 0.5 170 cm Waist at the navel on bare skin, after breathing out Example 80 ÷ 170 = 0.47 0.5 Below 0.5 — the adult guideline
Measure your waist at the navel and divide by your height in the same units. Below 0.5 is the broad guideline for adults; the ratio is not intended for children under 6 or during pregnancy.

The categories, and who they fit worst

CategoryBMIWorth knowing
UnderweightBelow 18.5Worth a conversation with a clinician — it carries its own risks, which get discussed far less than the other end of the scale.
Healthy18.5 – 24.9A reference band, not a target to chase. Plenty of healthy people sit just outside it.
Overweight25 – 29.9The band where BMI is least informative — it is where muscular builds and higher-fat builds collide.
30 and above30+Split into classes I–III. At this range BMI correlates more reliably with measured body fat.

Thresholds differ by population. The WHO recommends lower cut-offs for many Asian populations, where metabolic risk rises at a lower BMI — around 23 rather than 25 for the overweight boundary.

Where BMI does not apply

The formula was never built for children and teenagers, who are assessed on age-and-sex percentile charts instead. It is unreliable during pregnancy, in adults over about 70 as body composition shifts, and for anyone with a large muscle mass. If you are in one of those groups, the number on this page is not the right tool, and a clinician has better ones.

One note on how to hold this number. BMI is a screening signal, not a verdict on you, and a single figure cannot capture how healthy you are. If tracking weight or a number like this one tends to send your thoughts in a difficult direction, it is completely reasonable to skip it — and worth talking to a doctor or a registered dietitian who can look at the full picture with you.

Questions

Is BMI accurate for everyone?

No. It is a population-level screening tool. It cannot distinguish muscle from fat and does not account for where fat is stored, which makes it least reliable for athletes, older adults, pregnant women, and across different ethnic groups.

What should I measure instead?

Use waist-to-height ratio alongside it, as above. Because it captures abdominal fat specifically, it tracks metabolic risk more closely than BMI alone. Neither number is meaningful on its own — blood pressure, fasting glucose, and lipids tell you far more.

Why do BMI calculators disagree?

They shouldn't — BMI is one fixed formula. Differences come from unit rounding, or from calculators layering age and sex adjustments on top. This page uses the unmodified WHO formula: kg ÷ m².

References

  1. World Health Organization — Obesity and overweight, BMI classification
  2. CDC — About Adult BMI, including stated limitations
  3. NICE CG189 — Obesity identification and assessment, waist-to-height ratio guidance
  4. WHO expert consultation — appropriate BMI cut-off points for Asian populations, The Lancet

Reviewed September 2026. VitalTally calculators are informational and are not medical advice.