Health & fitness
Estimate adult body mass index from height and weight.
Enter your numbers to see the answer.
BMI calculator guide
Body mass index is a screening ratio that compares weight with height. This calculator takes weight in kilograms and height in centimetres, converts the height to metres, squares it, and divides the weight by that value to give a single BMI figure, then labels it with the adult range used by the World Health Organization: below 18.5 is underweight, 18.5 to 24.9 is the healthy-weight range, 25 to 29.9 is overweight, and 30 or above is classed as obesity. BMI is widely used because it needs only two measurements, which makes it useful for population studies and as a first check in a clinic, but it does not distinguish muscle from fat, does not show where fat is stored, and the adult thresholds do not apply to children, teenagers, pregnant women, or very muscular people. Treat the result as a screening estimate, not a diagnosis; a healthcare professional will interpret it alongside waist measurement, blood pressure, blood tests, history, and other context.
BMI = weight (kg) ÷ [height (m)]², where height (m) = height (cm) ÷ 100. Adult ranges: < 18.5 underweight; 18.5–24.9 healthy weight; 25.0–29.9 overweight; ≥ 30.0 obesity.
Worked example with the defaults: a weight of 70 kg and a height of 170 cm. Convert the height to metres, 170 ÷ 100 = 1.70 m, then square it: 1.70 × 1.70 = 2.89 m². Divide weight by that figure: 70 ÷ 2.89 = 24.22, which is the BMI the calculator displays, with the caption “healthy weight” because 24.22 falls between 18.5 and 24.9. The same person at 75 kg would have a BMI of 75 ÷ 2.89 = 25.95 and move into the overweight range, showing how a 5 kg change shifts the category near a threshold.
Enter weight in kilograms and height in centimetres, as labeled. Do not mix pounds with kilograms or inches with centimetres; convert first, using 1 lb = 0.4536 kg and 1 in = 2.54 cm. Someone who is 5 ft 7 in and 154 lb is 170 cm and 70 kg. If you prefer imperial arithmetic by hand, BMI = weight (lb) × 703 ÷ [height (in)]², which gives the same result.
Use BMI as one screening signal alongside history, waist measurement, fitness, age, and clinical context. Discuss concerns with a healthcare professional, especially if the result sits close to a threshold or you have a high muscle mass.
Do not interpret BMI as body-fat percentage, diagnosis, or a complete health assessment; a 90 kg rugby player at 180 cm has a BMI of 27.8 and may carry very little fat. Do not enter height in metres in the centimetre field, because 1.7 instead of 170 produces a BMI in the hundreds of thousands. Do not apply the adult ranges to anyone under 20, for whom age- and sex-specific percentile charts are used, or to pregnant women. Remember that some populations, including many people of South Asian descent, face higher metabolic risk at lower BMI values, so the cut-offs are not universal.
This is educational screening information, not medical advice or a treatment recommendation.
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How it works
Estimate adult body mass index from height and weight. This tool explains the calculation so you can adjust the assumptions to match your situation.
Worked example
With Weight = 70 kg · Height = 170 cm → 24.22 BMI (adult screening range: healthy weight). Change an input above and this example updates with your numbers.
Common questions
BMI is a ratio of weight to height used for screening and population comparison. A value of 24.22 for someone who is 70 kg and 170 cm indicates the healthy-weight range, but the number does not directly measure body fat, fitness, or health.
Yes. Muscle mass, age, sex, pregnancy, body composition, bone density, and population-specific guidance affect interpretation. Athletes can register as overweight with low body fat, and older adults may have a normal BMI with reduced muscle and higher fat.
The World Health Organization defines the adult healthy-weight range as a BMI of 18.5 to 24.9. Below 18.5 is classed as underweight, 25 to 29.9 as overweight, and 30 or more as obesity. These are screening categories, not a diagnosis.
Multiply weight in pounds by 703 and divide by height in inches squared. A 154 lb person who is 67 inches tall gets 154 × 703 ÷ (67 × 67) = 24.1, matching the metric result for 70 kg and 170 cm within rounding.
A BMI outside the 18.5–24.9 range is a reason to have a conversation, not a diagnosis. A clinician will consider waist circumference, blood pressure, blood sugar, cholesterol, family history, and lifestyle before recommending anything, so use the result as a screening prompt.