Health
BMI Calculator
Body mass index is a screening number that compares weight to height. Enter your height and weight in metric or imperial units to see your BMI, the WHO category it falls in, and the healthy weight range for your height.
How to use this calculator
- Choose metric or imperial units.
- Enter your height and weight.
- Read your BMI, its category and the healthy weight range for your height.
Formula
BMI = weight (kg) ÷ height (m)²
- weight
- body weight in kilograms
- height
- height in metres, so 170 cm is 1.70 m
Imperial inputs are converted to kilograms and centimetres before the same formula is applied.
Worked example
A person 170 cm tall weighing 70 kg.
- Height in metres170 ÷ 100 = 1.70
- Height squared1.70 × 1.70 = 2.89
- BMI70 ÷ 2.89
BMI is 24.2, which falls in the healthy weight category on the WHO adult scale.
What BMI can and cannot tell you
BMI was designed to describe populations, not individuals. It uses only height and weight, so it cannot tell muscle from fat, or account for body shape, bone structure, age, sex or where fat is distributed. A trained athlete and a sedentary person can share a BMI and have entirely different health profiles.
It remains useful as a starting point because it is quick, consistent and easy to track over time. It is a prompt for a conversation with a doctor, not a diagnosis.
BMI thresholds for Asian populations
Research has found that people of South Asian descent tend to develop weight-related health risks at lower BMI values than the standard international cut-offs suggest. Some Indian guidelines therefore use lower thresholds for overweight and obesity than the WHO categories shown here.
This calculator reports the standard WHO adult classification. If you are close to a boundary, a doctor can advise using thresholds appropriate to you.
Things to keep in mind
- These results are estimates and are not medical advice.
- BMI is not suitable for children, teenagers, pregnant women, athletes or older adults, who need age or condition-specific measures.
- Waist circumference and waist-to-height ratio can add useful information about where fat is carried.
Frequently asked questions
What is a healthy BMI?
The WHO classifies a BMI between 18.5 and 24.9 as healthy weight for adults. This is a population guideline, and some Indian guidelines use lower thresholds. A doctor can tell you what is appropriate for your situation.
Is BMI accurate for muscular people?
No. Muscle is denser than fat, so people with high muscle mass often have a BMI in the overweight range while carrying very little body fat. BMI cannot distinguish between the two.
Can BMI diagnose a health problem?
No. BMI is a screening measure only. It cannot diagnose any condition, and a result outside the healthy range is a reason to speak to a doctor rather than a conclusion in itself.
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