BMI Calculator
Body mass index (BMI) is a quick screening number that relates your weight to your height. Enter your weight and height below — in kilograms and centimetres, or pounds, feet and inches — and this calculator instantly shows your BMI along with the standard weight category it falls into: underweight, normal weight, overweight, or obesity.
BMI is used by doctors and health organisations because it is simple and works with measurements most people already know. It does not measure body fat directly, so athletes with high muscle mass can score high without excess fat. Treat the result as a starting point for a conversation about your health, not a final verdict.
How it works
The calculator converts your measurements to kilograms and metres if needed, divides your weight by your height squared, and matches the result against the World Health Organization's standard adult categories:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Formula
BMI = weight (kg) ÷ height (m)²
For imperial units, pounds are converted at 1 lb = 0.45359237 kg and inches at 1 in = 0.0254 m before applying the same formula. An equivalent shortcut is BMI = 703 × weight (lb) ÷ height (in)².
Worked example
Say you weigh 70 kg and are 1.75 m (175 cm) tall:
Height squared: 1.75 × 1.75 = 3.0625 m². BMI = 70 ÷ 3.0625 = 22.9, which lands in the Normal weight range (18.5 – 24.9). Entering the equivalent imperial figures (154.3 lb, 5 ft 8.9 in) gives the same result, because the calculator converts to metric behind the scenes.
This BMI calculator is a screening estimate for informational purposes only, not professional advice or a medical diagnosis. BMI does not account for muscle mass, age, or body composition — talk to a doctor or qualified health professional about what your result means for you.
Frequently asked questions
What is a healthy BMI for adults?
For most adults, a BMI between 18.5 and 24.9 is considered the healthy or normal-weight range by the World Health Organization. Below 18.5 counts as underweight, 25 to 29.9 as overweight, and 30 or above as obesity. These cut-offs apply to adults of all ages; children and teens use age- and sex-specific percentile charts instead.
How do I calculate BMI with pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. For example, at 160 pounds and 5 feet 10 inches (70 inches), you compute 703 times 160 divided by 4,900, which gives a BMI of about 23.0. This calculator does the conversion for you when you switch to imperial units.
Is BMI accurate for athletes and muscular people?
Not always. BMI only compares weight to height, so it cannot tell muscle from fat. Athletes and very muscular people often score in the overweight range while carrying little body fat. If you train heavily, measures such as waist circumference, waist-to-height ratio, or a body-fat assessment give a much clearer picture than BMI alone.
Does BMI differ for men and women?
The formula and the standard adult categories are identical for men and women. However, women typically carry more body fat than men at the same BMI, and body composition also shifts with age. That is one reason BMI is treated as a screening tool rather than a diagnosis, and why clinicians often pair it with other measurements.
What BMI is considered obese?
A BMI of 30 or higher falls in the obesity range for adults. Clinicians often subdivide it further: class 1 covers 30 to 34.9, class 2 covers 35 to 39.9, and class 3, sometimes called severe obesity, is 40 and above. A higher class is associated with greater health risk, but an evaluation by a doctor considers much more than BMI.