BMI Calculator – Calculate Your Body Mass Index Online
By Talcart · Last updated July 10, 2026
BMI Calculator Guide
Understanding BMI
BMI Formula
Metric: BMI = weight(kg) / height(m)²
Imperial: BMI = (weight(lb) × 703) / height(in)²
BMI Categories
Underweight: < 18.5
Normal weight: 18.5 - 24.9
Overweight: 25 - 29.9
Obese: ≥ 30
BMI Calculator – Calculate Your Body Mass Index Online
This BMI calculator divides your weight in kilograms by your height in meters squared: a 70 kg adult who is 1.75 m tall has a BMI of 22.9, inside the healthy 18.5-24.9 range. Enter your height and weight in metric or imperial units to get your Body Mass Index, your WHO weight category, and the weight range considered healthy for your height.
Key facts
- WHO adult BMI categories: under 18.5 underweight, 18.5-24.9 healthy weight, 25.0-29.9 overweight, 30.0 and above obesity.
- The CDC imperial formula is BMI = 703 x weight (lb) / height (in)^2, equivalent to the metric kg/m2 calculation.
- WHO estimates that in 2022 about 2.5 billion adults were overweight, of whom about 890 million were living with obesity.
- Obesity is subdivided by WHO into class I (30.0-34.9), class II (35.0-39.9), and class III (40.0+).
What is the BMI Calculator?
Body Mass Index (BMI) is a person's weight in kilograms divided by the square of their height in meters, used by the WHO and CDC as a screening measure for underweight, healthy weight, overweight, and obesity in adults. BMI does not measure body fat directly, but it correlates moderately well with body-fat levels across most of the adult population and with weight-related health risks such as type 2 diabetes and heart disease. Because it is a screening tool rather than a diagnosis, an out-of-range result is best discussed with a healthcare provider.
How does the BMI Calculator work?
The calculator applies the standard formula BMI = weight (kg) / height (m)^2. With imperial units it uses the CDC conversion BMI = 703 x weight (lb) / height (in)^2, which gives the same result. The output is compared against the WHO adult cutoffs — below 18.5 underweight, 18.5-24.9 healthy weight, 25.0-29.9 overweight, and 30.0 or above obesity — and the tool also back-solves the formula to show the weight range that would put your BMI between 18.5 and 24.9 at your height.
What is the BMI Calculator formula?
- weight – your body weight in kilograms (or pounds, with conversion)
- height – your height in metres (or inches, with conversion)
WHO adult BMI categories with example weights at 1.75 m (5 ft 9 in)
| Category | BMI (kg/m2) | Weight at 1.75 m |
|---|---|---|
| Underweight | Below 18.5 | Under 56.7 kg (125 lb) |
| Healthy weight | 18.5 - 24.9 | 56.7 - 76.5 kg (125 - 169 lb) |
| Overweight | 25.0 - 29.9 | 76.6 - 91.8 kg (169 - 202 lb) |
| Obesity class I | 30.0 - 34.9 | 91.9 - 107.1 kg (203 - 236 lb) |
| Obesity class II | 35.0 - 39.9 | 107.2 - 122.4 kg (236 - 270 lb) |
| Obesity class III | 40.0 and above | 122.5 kg (270 lb) and above |
How do you use the BMI Calculator?
- Choose your preferred unit system (metric or imperial).
- Enter your current height.
- Enter your current weight.
- Read your BMI value and the category it falls into.
Worked example
| Scenario | A 1.75 m tall adult who weighs 70 kg |
| Calculation | BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.86 |
| Result | BMI 22.86 → Healthy weight range (18.5 – 24.9). |
Common use cases
Tips & best practices
BMI is less accurate for very muscular people, pregnant women, and growing children.
Combine BMI with waist circumference for a fuller picture.
Frequently asked questions
A BMI between 18.5 and 24.9 kg/m2 is classified as healthy weight for adults by both the WHO and the CDC. Below 18.5 is underweight, 25.0-29.9 is overweight, and 30.0 or above is obesity. These cutoffs apply to adults aged 20 and over regardless of sex, though BMI is a screening measure and individual health risk depends on more than one number.
The same 18.5-24.9 healthy range applies to adult women and men — WHO and CDC adult BMI categories are not sex-specific. That said, women naturally carry a higher body-fat percentage than men at the same BMI, and BMI is not valid during pregnancy. Women tracking weight for health reasons should pair BMI with waist circumference and advice from a healthcare provider.
Divide your weight in kilograms by your height in meters squared. For example, 70 kg / (1.75 m x 1.75 m) = 22.9. With pounds and inches, multiply your weight by 703 and divide by your height in inches squared: a 154 lb person at 69 inches gets 703 x 154 / (69 x 69) = 22.7. Then compare the result against the 18.5 / 25 / 30 category cutoffs.
No — BMI often overestimates body fat in muscular people because muscle weighs more than fat per unit of volume. A strength athlete can register a BMI of 27-30 while carrying low body fat. The CDC notes BMI is a screening tool, not a measure of body composition, so athletes should rely on body-fat testing, waist circumference, or a clinical assessment instead.
A BMI of 30.0 or higher is classified as obesity in adults. The WHO subdivides it into class I (30.0-34.9), class II (35.0-39.9), and class III (40.0 and above), sometimes called severe obesity. Health risks such as type 2 diabetes, hypertension, and cardiovascular disease rise with each class, so a BMI in this range is a strong signal to consult a healthcare provider.
Not with adult cutoffs. For ages 2-19 the CDC interprets BMI using age- and sex-specific percentiles from growth charts: below the 5th percentile is underweight, the 5th to 84th is healthy weight, the 85th to 94th is overweight, and the 95th percentile or above is obesity. This calculator uses adult categories, so children's results should be assessed by a pediatrician.
Possibly. A WHO expert consultation found that many Asian populations face elevated risk of type 2 diabetes and cardiovascular disease at lower BMIs, and identified 23.0 and 27.5 kg/m2 as potential public-health action points alongside the standard cutoffs. Some countries apply lower thresholds accordingly. If you are of Asian descent, discuss the appropriate range with your healthcare provider.