How is BMI calculated?
BMI is calculated as weight in kilograms divided by height in metres squared, or as 703 times weight in pounds divided by height in inches squared. Enter your weight and height in FixDoks's BMI Calculator to see your BMI, your category under WHO or Asian cut-offs, and the healthy weight range for your height.
BMI Calculator at a glance
| Inputs | Weight, height, unit system, Asian cut-offs option |
|---|---|
| Output | BMI value, category, healthy weight range |
| Processing | In your browser; your files are not uploaded |
| Price | Free |
| Works on | Chrome, Edge, Safari and Firefox on Windows, Mac, Android and iPhone |
How to use BMI Calculator
- Choose kg / cm or lb / ft + in.
- Enter your weight and height.
- Tick Asian cut-offs if you are of South Asian origin.
- Read your BMI, category and healthy weight range.
What does BMI measure?
Body mass index compares your weight with your height. It is a quick screening number used by doctors and health programmes to spot adults who may be underweight or carrying excess weight. It does not measure body fat directly, and it cannot tell muscle from fat, so treat it as a starting point, not a diagnosis.
What is the BMI formula?
BMI = weight in kg ÷ (height in metres)²
In imperial units: BMI = 703 × weight in pounds ÷ (height in inches)².
Worked example
Weight 70 kg, height 170 cm.
- Height in metres = 1.70, and 1.70² = 2.89
- BMI = 70 ÷ 2.89 = 24.2
- Healthy range for 170 cm (BMI 18.5 to 24.9) = 53.5 kg to 72.0 kg
Under WHO cut-offs, 24.2 is a healthy weight. Under the Asian cut-offs, it falls in the overweight band, which starts at 23.
BMI categories
| Category | WHO (global) | Asian cut-offs |
|---|---|---|
| Underweight | Below 18.5 | Below 18.5 |
| Healthy weight | 18.5 to 24.9 | 18.5 to 22.9 |
| Overweight | 25 to 29.9 | 23 to 24.9 |
| Obese | 30 and above | 25 and above |
Why lower cut-offs for South Asians?
Research summarised by the WHO found that many Asian populations develop type 2 diabetes and heart disease risk at lower BMI levels than European populations, because they tend to carry more body fat at the same BMI. Indian clinical guidelines therefore use 23 as the start of overweight and 25 as the start of obesity for adults. Tick the box above to apply these.
Imperial example
Weight 154 lb, height 5 ft 7 in (67 inches). BMI = 703 × 154 ÷ 67² = 108,262 ÷ 4,489 = 24.1, which matches the metric result for the same person after rounding.
Limits of BMI
- Athletes and very muscular people can have a high BMI with low body fat.
- Older adults may lose muscle and have a normal BMI with high body fat.
- Children and teenagers need age and sex specific BMI charts. This calculator is for adults aged 18 and over.
- Pregnancy changes weight in ways BMI does not account for.
If your BMI is outside the healthy range, small and steady changes to diet, sleep and activity usually work better than crash diets. A change of 5% of body weight is already linked with better blood sugar and blood pressure in people who are overweight.
Waist size adds useful information. A waist above about 90 cm for Indian men or 80 cm for Indian women is linked with higher risk even at a normal BMI. For personal advice about weight, talk to a doctor or a registered dietitian.