| Weight | Height | BMI | Category | Note |
| {y} |
Online BMI Calculator — Body Mass Index
This tool calculates your BMI (Body Mass Index) for free from your weight and height. The result is displayed immediately, along with your weight category according to the World Health Organization (WHO) classification and your ideal weight range.
What is BMI?
The Body Mass Index is an indicator used to estimate an adult's body composition and evaluate the health risks associated with being overweight or underweight. It was devised in the 19th century by the Belgian mathematician Adolphe Quetelet — it is sometimes called the Quetelet index.
How is BMI calculated?
The BMI formula is as follows:
Metric: BMI = weight (kg) ÷ height² (m)
US: BMI = 703 × weight (lb) ÷ height² (in)
For example, for a person weighing 70 kg (154 lb) and measuring 1.75 m (5 ft 9 in): BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.86. This value corresponds to a normal weight.
With our calculator you don't have to do any conversion yourself: pick metric or US units and simply enter your height and weight — the tool handles the rest.
How to use this calculator?
First choose your unit system: Metric (kilograms and centimeters) or US (pounds, feet and inches). Then enter your weight and height. The BMI, the weight category and the ideal weight range are calculated automatically and shown in the units you selected. The Clear button resets the fields.
Behind the scenes the US values are converted to metric (1 lb ≈ 0.4536 kg, 1 inch = 2.54 cm), so both systems give the exact same BMI. For example, 154 lb and 5 ft 9 in match 70 kg and 175 cm.
WHO BMI categories
The WHO classifies adult BMI (18 to 65 years old) according to the following thresholds:
| BMI (kg/m²) | Category |
|---|---|
| Below 16.5 | Severe thinness (undernutrition) |
| 16.5 to 18.5 | Underweight |
| 18.5 to 25 | Normal weight |
| 25 to 30 | Overweight |
| 30 to 35 | Moderate obesity (class I) |
| 35 to 40 | Severe obesity (class II) |
| 40 and above | Morbid obesity (class III) |
What is the ideal weight?
The calculator also displays your ideal weight range, that is, the weight interval corresponding to a BMI between 18.5 and 25 (normal weight) for your height. It is an indication, not a strict goal: the "ideal" figure also depends on muscle mass, bone structure and lifestyle.
The limits of BMI
BMI is a simple and useful indicator, but it has its limits. It does not distinguish between fat mass and muscle mass: a very muscular athlete can have a high BMI without being overweight. It is also not suited to children, pregnant women, the elderly, or very tall or very short people. If you have any doubts about your weight or health, consult a doctor.
Saving and results history
You can record your results in the history by clicking the Save button. It's handy for tracking the evolution of your BMI over time. Each cell of the table is editable and you can export the history in CSV or PDF format.
Keyboard shortcuts
You can use keyboard keys to save time.
m ⇝ Clear
f ⇝ Save
Other health tools
To track your diet, also check out our calorie, protein, carb and fat counter.