BMI calculator

The number is a starting point, not a verdict

BMI is a screening measure built for looking at populations, and it is used on individuals because it is cheap and quick, not because it is precise. It knows two things about you — your height and your weight — so there is a great deal it cannot know.

• It cannot tell muscle from fat. A muscular athlete can read as obese; someone with very little muscle can read as normal while carrying a lot of fat.
• It does not know where the fat is, and that matters more for risk than the total. Waist measurement carries information BMI does not.
• It is not valid for children and teenagers, who are assessed against percentiles for their age and sex, or during pregnancy.
• It says nothing about your blood pressure, blood sugar or cholesterol, which are what the risk is actually about.

If the number concerns you, it is a reason to talk to a doctor, not a diagnosis on its own. This page is a calculator, not medical advice.

Why two scales

The thresholds most people know — 18.5, 25, 30 — are the WHO international ones, and they were derived largely from European populations. The WHO's 2004 expert consultation examined Asian populations and found that the risk of type 2 diabetes and cardiovascular disease rises at a lower BMI, and identified additional public-health action points at 23.0 and 27.5. Several South Asian guidelines went further, treating 23 as overweight and 25 as obese.

That is not a small difference. A BMI of 24 is comfortably "normal" internationally and "increased risk" on the Asian cut-offs. Most calculators show only the first number. For anyone reading this page from Pakistan or the wider region, the second is likely to be the more relevant one — so both are shown, labelled, rather than one being quietly presented as the truth.

The two scales side by side

• Under 18.5 — underweight on both.
• 18.5 to 23 — normal on both.
• 23 to 25 — normal internationally; increased risk on the Asian cut-offs.
• 25 to 27.5 — overweight internationally; high risk on the Asian cut-offs.
• 27.5 to 30 — overweight internationally; very high risk on the Asian cut-offs.
• 30 and above — obese internationally; very high risk on the Asian cut-offs.

Questions

How is BMI worked out?

Weight in kilograms divided by height in metres squared. In imperial, pounds divided by inches squared, times 703. The calculator converts either way for you.

Why do South Asians have different BMI thresholds?

Because the risk starts earlier. The WHO's 2004 expert consultation found that in Asian populations the risk of type 2 diabetes and cardiovascular disease rises at a lower BMI than in European populations, and identified additional public-health action points at 23.0 and 27.5. Several South Asian guidelines treat 23 as overweight and 25 as obese. A BMI of 24 is therefore normal on one scale and raised on the other, which is why both are shown here.

What is a healthy BMI?

18.5 to 25 on the WHO international scale; 18.5 to 23 on the Asian cut-offs. The calculator turns both into an actual weight range for your height, which is more useful than the number.

Is BMI accurate?

It is a screening measure for populations, not a diagnosis for an individual. It uses only height and weight, so it cannot tell muscle from fat — a muscular athlete can read as obese while someone with little muscle can read as normal while carrying a lot of fat. It also does not account for where fat is carried, which matters more for risk than the total. It is not valid for children and teenagers, who are assessed on percentiles for their age and sex, or during pregnancy.

Does it work for children?

No, and no adult BMI calculator does. Children and teenagers are assessed on percentiles for their age and sex — a paediatrician or a growth chart is the right tool, not this one.

Is my data sent anywhere?

No. Your height and weight are health data. The calculation happens in your browser and the page makes no network request carrying it. Nothing is stored either.

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