BMI Calculator – Check Your Body Mass Index (Metric & Imperial)
BMI Calculator
Calculate your Body Mass Index quickly to evaluate if you are at a healthy weight for your height and gender.
* BMI is an estimate of body fat and a good measure of your patients' risk for diseases that can occur with more body fat. It applies to both adult men and women.
Quick answer
A BMI calculator divides your weight in kilograms by your height in metres squared: BMI = kg ÷ m². For adults, a BMI under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight and 30 or more is obese. For example, 72 kg at 175 cm gives a BMI of 23.5, which is in the healthy range.
Our free BMI calculator works out your Body Mass Index in a second and tells you which weight category you fall into. You can enter your height and weight in metric (kg and cm) or imperial (lbs, feet and inches), and the colour scale shows at a glance where your number sits.
BMI is the screening measure used by the World Health Organization and most doctors as a quick first check of weight. It is not a diagnosis, but it is a useful starting point for a conversation about health.
What Is BMI?
Body Mass Index (BMI) is a number that compares your weight with your height. Because taller people naturally weigh more, BMI scales weight by height squared so that people of different heights can be compared on the same chart. The result is grouped into standard adult categories that are linked to health risk.
A BMI calculator is popular because it needs only two measurements and no equipment beyond a scale and a tape measure, yet it gives a consistent answer anyone can track over time.
How to Use the BMI Calculator
Follow these four steps to get your BMI:
Step 1: Choose Your Units and Gender
Select Metric (kg/cm) or Imperial (lbs/ft) depending on how you measure, then pick Male or Female. The units switch changes the height and weight boxes for you.
Step 2: Enter Your Age, Height and Weight
Type your Age, your Height (in cm, or feet and inches) and your Weight (in kg or lbs). Measure without shoes and in light clothing for the most accurate BMI.
Step 3: Click Calculate BMI
Press Calculate BMI. The BMI calculator converts your height to metres, squares it and divides your weight by the result.
Step 4: Read Your BMI and Category
Your BMI appears in the circle with a label such as Normal Weight. The coloured bar underneath marks the four ranges (Under, Normal, Over and Obese) so you can see how close you are to the next category.
BMI Formula
BMI = 703 × weight (lb) ÷ height (in)²
Metric example: 72 kg and 175 cm. Height in metres is 1.75, and 1.75² = 3.0625. 72 ÷ 3.0625 = 23.5.
Imperial example: 160 lb and 5 feet 9 inches (69 inches). 69² = 4,761. 703 × 160 ÷ 4,761 = 23.6. Both people fall in the healthy weight range.
BMI Categories for Adults
These are the standard WHO categories the BMI calculator uses for adults aged 20 and over:
| BMI | Category | What it suggests |
|---|---|---|
| Below 18.5 | Underweight | May point to low energy intake or another health issue |
| 18.5 to 24.9 | Healthy weight | Lowest weight-related health risk for most adults |
| 25.0 to 29.9 | Overweight | Raised risk of high blood pressure and type 2 diabetes |
| 30.0 and above | Obese | Higher risk; talk to a doctor about a plan |
Some health bodies use lower cut-offs for people of South Asian, Chinese and other Asian backgrounds, for example treating a BMI of 23 or more as overweight, because health risks start at a lower BMI. If that applies to you, read your result with that in mind.
BMI Examples
| Height | Weight | BMI | Category |
|---|---|---|---|
| 160 cm | 50 kg | 19.5 | Healthy weight |
| 165 cm | 75 kg | 27.5 | Overweight |
| 175 cm | 72 kg | 23.5 | Healthy weight |
| 180 cm | 100 kg | 30.9 | Obese |
| 170 cm | 52 kg | 18.0 | Underweight |
Limitations of BMI
- Muscle vs fat: athletes with a lot of muscle can have a high BMI without excess fat.
- Body shape: BMI does not show where fat is stored; waist size is a better guide to belly fat.
- Age: older adults may lose muscle, so a "normal" BMI can still hide low muscle mass.
- Children and teens: under 20s need BMI-for-age percentiles, not the adult categories.
- Pregnancy: BMI is not meaningful during pregnancy.
Use your BMI alongside other checks such as waist circumference, blood pressure and blood tests, and talk to a healthcare professional before making big changes.
Tips for a Healthy BMI
- Track the trend, not one number: check your BMI every few weeks at the same time of day.
- Eat mostly whole foods: vegetables, fruit, lean protein and whole grains help manage weight steadily.
- Move every day: aim for at least 150 minutes of moderate activity a week, plus strength training.
- Sleep well: poor sleep is linked to weight gain.
- Set small goals: losing 5% of body weight already brings real health benefits for many people.
Why Use This BMI Calculator?
- Metric or imperial: switch units with one click.
- Visual scale: see your category on a colour bar, not just a number.
- Private: your measurements never leave your device.
- Free: no sign-up, works on phone, tablet and laptop.
Frequently Asked Questions
What is a healthy BMI?
For most adults a BMI between 18.5 and 24.9 is considered a healthy weight. Some guidelines use a lower upper limit of about 23 for people of Asian background.
How do I calculate BMI by hand?
Divide your weight in kilograms by your height in metres squared. In pounds and inches, multiply weight by 703 and divide by height in inches squared. The BMI calculator does this instantly.
Is BMI different for men and women?
The adult BMI formula and categories are the same for men and women. Women naturally carry more body fat at the same BMI, which is one reason BMI is only a screening tool.
Is BMI accurate for athletes?
Not always. Muscle weighs more than fat, so very muscular people can show an overweight BMI while having low body fat.
Can children use this BMI calculator?
The adult categories do not apply to children and teenagers. Under 20s should use BMI-for-age percentile charts with a doctor.
Is my data saved?
No. The BMI calculator runs entirely in your browser and nothing you type is stored.