How to calculate your BMI and what the result means
Body mass index (BMI) is a number that relates your weight to your height. Health bodies use it as a first screening tool to see whether an adult's weight is in the usual range for their height. It is useful if you have started a programme to lose or gain weight and want to track progress, if a gym or insurance form asks for it, or if you simply want a general idea of where you stand.
This calculator gives you the number and its category in one step. The calculation runs in your browser, and your weight and height are not stored or sent anywhere.
How to use it
- Enter your weight in kilograms in "Weight (kg)".
- Enter your height in centimetres in "Height (cm)".
- Press "Calculate BMI".
- The result appears with one decimal place followed by the category, for example 22.9 — Normal weight.
How it is calculated and classified
- Formula: weight in kg ÷ (height in metres × height in metres). Centimetres are converted to metres automatically.
- Below 18.5: Underweight.
- 18.5 to under 25: Normal weight.
- 25 to under 30: Overweight.
- 30 and above: Obese. The calculator does not split obesity into classes.
- These cut-offs are the World Health Organization's classification for adults.
Practical examples
- 70 kg and 175 cm gives a BMI of about 22.9, within the normal range.
- 95 kg and 180 cm gives about 29.3, in the overweight range and close to the obesity threshold.
- Monthly tracking during a diet: calculate on the same day each month and watch the trend rather than a single reading.
- If you use pounds and inches, convert first: one pound is about 0.4536 kg and one inch is 2.54 cm, because the calculator accepts metric units only.
Important health notes
- BMI is a general indicator, not a diagnosis. It does not measure body fat or where fat is stored, and it does not account for age or sex.
- The adult categories do not apply during pregnancy or to children and teenagers, who are assessed with growth charts.
- The WHO notes that some populations, including some Asian populations, may face health risks at lower values than the standard cut-offs.
- For a proper assessment, speak to a doctor or dietitian, who may also use measures such as waist circumference.
- Weigh yourself under similar conditions, such as in the morning before eating, so readings are comparable.
To estimate your daily energy needs, use the calorie calculator, and to estimate how much water you need each day, try the water intake calculator.