What is a healthy BMI?

For adults, the WHO considers 18.5–24.9 the normal range. Below 18.5 counts as underweight, 25–29.9 as overweight, and 30 or above as obese. BMI is a general screening guide, not a diagnosis.

Is BMI accurate for athletes and muscular people?

Not very. Muscle is denser than fat, so strength athletes and heavily muscled people often land in the overweight range while carrying little body fat. If you train hard, a body fat estimate tells you much more than BMI does.

Is the formula different for men and women?

No — the same formula and the same adult cutoffs apply to everyone. Women typically carry more body fat than men at the same BMI, which is one reason BMI is treated as a rough screen rather than a body-composition measurement.

Can I use this calculator for a child or teenager?

No. For anyone under about 18, BMI has to be compared against age- and sex-specific growth percentiles, not the fixed adult cutoffs this tool uses. A pediatrician can plot BMI-for-age correctly.

My BMI is normal but my waistline keeps growing. Should I care?

Yes, it’s worth attention. BMI says nothing about where fat sits, and fat stored around the abdomen carries more health risk than fat on the hips or thighs. A steadily rising waist measurement is worth mentioning to your doctor even when BMI looks fine.

When should I talk to a doctor about my BMI?

If your BMI falls outside 18.5–24.9, if it’s changing quickly without an obvious reason, or before you start a major diet or training program. Overall health risk also depends on blood pressure, blood sugar, cholesterol, and family history — things a single number can’t capture.

No — the calculation runs entirely in your browser. Your weight and height are never sent to a server or stored anywhere.

BMI Calculator

Calculate your Body Mass Index and see your weight category instantly.

Runs in your browser — files never leave your device

WeightkgHeightcm

BMI

22.9

How it works

Body Mass Index (BMI) is a screening number that relates your weight to your height. It’s the measure most public-health bodies, including the World Health Organization (WHO), use to sort adult weight into broad categories associated with health risk. It doesn’t measure body fat directly — it’s a fast first check, not a diagnosis.

The calculator uses the standard formula: BMI = weight in kilograms ÷ height in meters squared. Your height in centimeters is converted to meters, and the result is rounded to one decimal place before a category is assigned. Worked example: at 70 kg and 175 cm, height is 1.75 m, so BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.86, which the tool rounds and displays as 22.9 — inside the normal range.

The category shown next to your number follows the WHO cutoffs for adults:

BMI (kg/m²)	Category
Below 18.5	Underweight
18.5–24.9	Normal
25.0–29.9	Overweight
30.0 and above	Obese

Read the result as a starting point rather than a verdict. The trend matters more than any single reading — a number drifting toward a boundary over months says more than where you sit today. If you’re within a few tenths of a cutoff, small differences in how you weigh or measure yourself can flip the category, so don’t over-interpret the label.

BMI has well-known blind spots: it can’t separate muscle from fat, it ignores where fat is stored (abdominal fat is riskier), it isn’t valid during pregnancy, and children need age-based percentiles instead. Health risk can also begin at lower BMI values in some groups — WHO notes this for many South and East Asian populations. Treat the result as general guidance only — not medical advice; a clinician can put your number in context.

Frequently asked questions

What is a healthy BMI?: For adults, the WHO considers 18.5–24.9 the normal range. Below 18.5 counts as underweight, 25–29.9 as overweight, and 30 or above as obese. BMI is a general screening guide, not a diagnosis.
Is BMI accurate for athletes and muscular people?: Not very. Muscle is denser than fat, so strength athletes and heavily muscled people often land in the overweight range while carrying little body fat. If you train hard, a body fat estimate tells you much more than BMI does.
Is the formula different for men and women?: No — the same formula and the same adult cutoffs apply to everyone. Women typically carry more body fat than men at the same BMI, which is one reason BMI is treated as a rough screen rather than a body-composition measurement.
Can I use this calculator for a child or teenager?: No. For anyone under about 18, BMI has to be compared against age- and sex-specific growth percentiles, not the fixed adult cutoffs this tool uses. A pediatrician can plot BMI-for-age correctly.
My BMI is normal but my waistline keeps growing. Should I care?: Yes, it’s worth attention. BMI says nothing about where fat sits, and fat stored around the abdomen carries more health risk than fat on the hips or thighs. A steadily rising waist measurement is worth mentioning to your doctor even when BMI looks fine.
When should I talk to a doctor about my BMI?: If your BMI falls outside 18.5–24.9, if it’s changing quickly without an obvious reason, or before you start a major diet or training program. Overall health risk also depends on blood pressure, blood sugar, cholesterol, and family history — things a single number can’t capture.
Is my data uploaded?: No — the calculation runs entirely in your browser. Your weight and height are never sent to a server or stored anywhere.

BMI Calculator

How it works

Frequently asked questions

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