What is BMI?
Body Mass Index (BMI) is a simple number that compares your weight with your height. Doctors and health workers use it as a quick first check to see whether a person’s weight is likely to be in a healthy range. It cannot tell you everything about your health, but because it needs only two measurements, it is one of the most widely used screening tools in the world.
This calculator works in both metric (centimetres and kilograms) and imperial (feet, inches and pounds) units, shows where your result falls on the BMI scale, and tells you the healthy weight range for your height.
How to Use the BMI Calculator
- Select Metric or Imperial.
- Enter your height — in centimetres, or in feet and inches.
- Enter your weight in kilograms or pounds.
- Your BMI, its category and the healthy weight range for your height appear instantly. Tap Copy to save the result.
For the most consistent results, weigh yourself in the morning, before breakfast and in light clothing.
BMI Formula
Example: Height 170 cm (1.70 m), weight 68 kg. BMI = 68 ÷ (1.70 × 1.70) = 68 ÷ 2.89 = 23.5.
In imperial units the formula is BMI = 703 × weight (lb) ÷ height (in)2. The calculator converts automatically, so you don’t need to do this yourself.
BMI Categories
| BMI | WHO category | Asian Indian guideline |
|---|---|---|
| Below 18.5 | Underweight | Underweight |
| 18.5 – 22.9 | Normal | Normal |
| 23.0 – 24.9 | Normal | Overweight |
| 25.0 – 29.9 | Overweight | Obese |
| 30 and above | Obese | Obese |
The calculator shows the standard WHO categories. If you are of South Asian origin, it is worth keeping the stricter Indian thresholds in mind: in the example above, a BMI of 23.5 is “normal” by WHO standards but at the start of the “overweight” band under Indian guidelines.
Healthy Weight Range for Your Height
By rearranging the formula, you can find the weight range that corresponds to a BMI of 18.5 to 24.9:
| Height | Healthy weight (WHO) |
|---|---|
| 150 cm (4′11″) | 41.6 – 56.0 kg |
| 160 cm (5′3″) | 47.4 – 63.7 kg |
| 170 cm (5′7″) | 53.5 – 72.0 kg |
| 180 cm (5′11″) | 59.9 – 80.7 kg |
Limitations of BMI
- Muscle vs fat: a muscular athlete can have a BMI over 25 with very little body fat.
- Where fat is stored: fat around the waist carries more health risk than fat elsewhere, and BMI cannot see this. Measuring your waist adds useful information.
- Age and sex: women naturally have more body fat than men at the same BMI, and older adults lose muscle over time.
- Pregnancy: BMI is not meaningful during pregnancy.
If Your BMI is Outside the Healthy Range
A single number is not a reason to panic. Small, steady changes work better than crash diets: regular meals with more vegetables, pulses and protein, fewer sugary drinks and fried snacks, at least 150 minutes of moderate activity a week, and enough sleep. If your BMI is well above or below the healthy range, or you have conditions such as diabetes or high blood pressure, talk to a doctor or registered dietitian for advice suited to you.
Related Tools
- Weight Converter — convert between kg, pounds and stone.
- Length Converter — convert your height between feet, inches and centimetres.
- Age Calculator — find your exact age.