BMI Calculator

What BMI measures

Body Mass Index (BMI) is a simple number that relates your weight to your height. It’s widely used as a quick screening tool to sort people into broad weight categories. It does not measure body fat directly, but for most people it correlates well enough to be a useful first check.

The formula

BMI is weight divided by height squared:

• Metric: BMI = kg ÷ (m × m) — for example, 70 kg at 1.75 m is 70 ÷ 3.0625 ≈ 22.9.
• Imperial: BMI = 703 × lb ÷ (in × in) — the 703 factor converts pounds and inches into the metric result.

This calculator does the unit conversion for you — just switch between Metric and Imperial.

BMI categories (adults)

• Below 18.5 — underweight
• 18.5 to 24.9 — healthy weight
• 25 to 29.9 — overweight
• 30 and above — obese

These standard cut-offs come from the World Health Organization and apply to adults aged 20 and over. Some health bodies use lower thresholds for people of South and East Asian descent, where health risks can rise at a lower BMI.

Important limitations

BMI is a screening number, not a diagnosis. Because it only uses height and weight, it can be misleading for some people:

• Muscular people (athletes, weightlifters) may have a high BMI with low body fat.
• Older adults may have a “normal” BMI but reduced muscle mass.
• Children and teens need age- and sex-specific percentile charts, not these adult bands.
• It says nothing about where fat is stored, which matters for health risk.

Treat your BMI as a starting point for a conversation with a doctor, not a verdict on your health.

FAQ

Is a “healthy” BMI a guarantee of good health?

No. Blood pressure, fitness, diet, and family history all matter and aren’t captured by BMI.

Which unit system is more accurate?

Neither — they produce the same BMI. Use whichever you have your measurements in.

Is this BMI calculator free, and is my data private?

Yes, it's free with no account needed, and your height and weight never leave your device. The BMI is computed entirely in your browser, so nothing is uploaded, logged, or stored.

Can I use this BMI calculator for my child?

No. The adult categories shown here don't apply to children and teenagers, whose healthy ranges change with age and sex. For anyone under 20, use a pediatric BMI-for-age percentile chart from a doctor or a children's health authority instead.

Should athletes rely on BMI?

Not on its own. Because BMI only uses height and weight, very muscular people such as athletes and weightlifters can land in the "overweight" or "obese" range despite low body fat. For them, a body fat measurement or waist circumference is a more meaningful indicator.

Does it work on my phone?

Yes. The calculator is fully responsive and works in any modern mobile browser — just type your height and weight and the BMI updates instantly, no app to install.