Fitness calculator
BMI Calculator
Calculate your body mass index in metric or imperial units, see which category it falls into, and find your healthy weight range.
Your BMI
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What is BMI?
Body mass index (BMI) is a screening measure that relates weight to height. It is used to broadly categorize weight status in adults, though it does not directly measure body fat or account for muscle mass, age, or body composition.
BMI formula
With imperial units, the formula uses a conversion factor of 703:
BMI categories for adults
The standard adult BMI categories used by health organizations are: below 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 or above is obesity.
Example
Suppose someone is 175 cm tall and weighs 70 kg. Their height in meters is 1.75.
A BMI of 22.9 falls within the normal weight range of 18.5 to 24.9.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered the normal weight range.
Is BMI accurate for everyone?
No. BMI is a screening tool, not a diagnosis. It can overestimate body fat in muscular people and underestimate it in older adults. Athletes, pregnant women, and children are measured differently. Talk to a healthcare provider for a full assessment.
How do I calculate BMI with pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. Calquo does this conversion automatically in imperial mode.
Is BMI different for children?
Yes. For children and teens, BMI is compared against age- and sex-specific percentiles rather than the fixed adult categories. This calculator is intended for adults.
How the BMI calculator works
Body mass index is a single number that relates your weight to your height. The calculator divides your weight in kilograms by the square of your height in meters. If you enter pounds and inches instead, it converts them first, so both unit systems give the same result.
Alongside the BMI value you get the World Health Organization category it falls into and the weight range that would put you in the normal band for your height. That range is worked out by reversing the formula at BMI 18.5 and 24.9.
BMI formula
The factor of 703 in the imperial version is simply the unit conversion folded into one number, so you do not have to convert pounds and inches by hand. For example, someone who is 1.75 m tall and weighs 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In imperial units that is 154 lb and 69 in: 703 × 154 ÷ (69 × 69) = 22.7, with the small difference coming from rounding the height.
BMI categories for adults
The calculator uses the standard adult ranges published by the World Health Organization and used by the CDC and NHS:
- Below 18.5 – underweight
- 18.5 to 24.9 – normal weight
- 25.0 to 29.9 – overweight
- 30.0 and above – obesity
What BMI can and cannot tell you
BMI is a quick screening measure, not a diagnosis. It works well for spotting trends across large groups of people, but it only knows your height and weight. It cannot tell muscle from fat, so athletes and people who lift weights often read as overweight despite having low body fat. It also does not account for where fat is stored, and it is calibrated for adults rather than children, teenagers, or people who are pregnant.
For that reason, a BMI outside the normal range is best treated as a prompt to look at other measures such as waist circumference, blood pressure, and how you feel day to day, ideally with a doctor or nurse.
Frequently asked questions
What is a healthy BMI?
For adults, a BMI between 18.5 and 24.9 is classified as normal weight. The calculator shows the exact weight range that corresponds to that band for your height.
How do I calculate BMI with pounds and inches?
Multiply your weight in pounds by 703, then divide by your height in inches squared. Switching the calculator to imperial does this conversion for you.
Is BMI the same for men and women?
Yes. The adult BMI formula and categories are identical for men and women, even though women tend to carry a higher percentage of body fat at the same BMI.
Does BMI work for children and teenagers?
Not with these adult ranges. For anyone under 20, BMI is compared against age- and sex-specific growth charts and expressed as a percentile. This calculator is designed for adults.
Why is my BMI high if I am muscular?
BMI only uses height and weight, so it cannot distinguish muscle from fat. Muscle is denser than fat, which pushes heavily muscled people into the overweight or obese range even when their body fat is low.
This calculator is for informational and educational purposes only and is not medical advice. Its results are general estimates, not an individual assessment. Talk to a doctor, registered dietitian, or other qualified health professional before making decisions about your health, diet, or exercise.