BMI Calculator

How to use this calculator

1. Choose Metric (centimetres and kilograms) or Imperial (feet, inches and pounds).
2. Enter your height and weight in the selected units.
3. Press Calculate BMI to see your BMI, your WHO category and the healthy weight range for your height.
4. After the first result, the figure and the marker on the colored scale update automatically as you adjust your numbers.

Other Units opens a converter above the calculator. It is not a third unit system: use it when your scales read in stones or your tape reads in metres, then type the converted figure into the boxes. The calculator stays on whichever system you chose.

What Body Mass Index is

Body Mass Index is a single number that relates your weight to your height, used to screen adults for underweight, healthy weight, overweight and obesity. It needs only two measurements and no equipment, which is why clinicians and public-health bodies reach for it as a first-pass indicator. It estimates whether your weight is in a healthy proportion to your height — not how that weight is made up.

The BMI formula

In metric units, BMI is your weight in kilograms divided by the square of your height in metres:

BMI = weight(kg) / height(m)²

• weight — your body weight in kilograms
• height — your height in metres (175 cm = 1.75 m)

Working in imperial units, the equivalent is 703 × weight(lb) / height(in)². The calculator converts your entries for you, so both systems return the same BMI to within rounding.

A worked example

Take someone 175 cm tall weighing 70 kg. Their height in metres is 1.75, and 1.75² = 3.0625, so BMI = 70 ÷ 3.0625 ≈ 22.9. That sits in the 18.5–24.9 band, a healthy weight. Entered in imperial units (about 5 ft 9 in and 154 lb) the same person comes out at 22.9 as well — the calculator converts between the systems for you.

Interpreting your result

The World Health Organization sorts adult BMI into four bands:

BMI	Category
Below 18.5	Underweight
18.5 – 24.9	Healthy weight
25.0 – 29.9	Overweight
30.0 and above	Obesity

The colored scale marks where you fall between these bands, and the result also shows the healthy weight range for your height — the weights that correspond to a BMI of 18.5 to 24.9. For someone 175 cm tall that range is roughly 56.7 kg to 76.3 kg.

Where BMI falls short

BMI counts all weight the same, so it cannot tell muscle from fat or say where fat is stored. A muscular athlete may register as "overweight" with very little body fat, while an older adult who has lost muscle may sit in the "healthy" band yet carry elevated risk. Waist circumference, body-fat percentage and blood markers add the detail BMI leaves out.

• Adults only. These cut-offs apply to people aged 20 and over; children and teens use age- and sex-specific BMI-for-age percentiles.
• No body-composition detail. Two people with the same BMI can differ greatly in muscle and fat.
• A screen, not a diagnosis. BMI flags who may benefit from a closer look, not a verdict on any individual's health.

Related calculators

To see how much of your weight is fat rather than muscle, use the body fat calculator; to find a weight target from height and sex, try the ideal weight calculator. This is educational information, not medical advice. Speak with a qualified healthcare provider about your individual health.