BMI Calculator: Check Your Body Mass Index
Use this BMI calculator to check your body mass index in seconds. Enter your height and weight and see which range you fall in.
BMI is a quick screening number, not a diagnosis.
Informational site. This content is not medical advice and does not replace a doctor, nutritionist or other health professional. BMI is only a general screening reference.
BMI calculator
BMI calculator
BMI is weight in kilograms divided by height in meters squared. In imperial units it is 703 times weight in pounds divided by height in inches squared.
BMI ranges for adults
- Below 18.5: underweight
- 18.5 to 24.9: healthy weight
- 25 to 29.9: overweight
- 30 to 34.9: obesity class 1
- 35 to 39.9: obesity class 2
- 40 or more: obesity class 3
What BMI does not show
BMI does not measure body fat, muscle mass or where fat is stored. Athletes and older adults can get results that do not reflect their health. Talk to a health professional to interpret your number.
How to use the BMI calculator step by step
- Measure your height without shoes, standing straight, and write it in centimeters or inches.
- Weigh yourself in the morning, before eating, wearing light clothes, and write it in kilograms or pounds.
- Choose the unit system in the calculator, metric or imperial, so the numbers match what you typed.
- Press the calculate button and read the number and the range shown below it.
- Compare the result with the ranges on this page and keep the number to follow your progress over time.
Small measuring errors change the result. A difference of two centimeters in height or two kilos in weight can move your BMI by a few tenths, so always measure the same way when you want to compare results.
Examples of BMI results
A person who is 1.70 m tall and weighs 70 kg has a BMI of about 24.2, which is inside the healthy range. Someone with the same height who weighs 85 kg has a BMI near 29.4, which is at the upper end of the overweight range. A person who is 1.80 m tall and weighs 55 kg has a BMI near 17.0, which is below the healthy range.
These examples show why the number needs context. Two people with the same BMI can have very different amounts of muscle, different ages and different health histories.
Common mistakes when calculating BMI
- Mixing units, such as typing pounds while the calculator is set to kilograms.
- Typing height in meters when the field expects centimeters.
- Using an old weight from months ago instead of a recent measurement.
- Treating the number as a final judgment instead of a general screening reference.
- Comparing the adult ranges with results for children and teenagers.
When BMI is less reliable
BMI can be misleading for people who train with weights, because muscle weighs more than fat and the number may look high even with low body fat. It can also be less accurate for older adults who lost muscle, for pregnant women and for people with very short or very tall builds. In these cases other measures, such as waist circumference, body composition tests and blood work, give a more complete picture.
Everyday habits that support a healthy weight
Regular physical activity, balanced meals with vegetables, fruit and fiber, enough sleep and drinking water are habits commonly recommended by health organizations. Changes are more lasting when they are gradual and realistic. Avoid extreme diets and products that promise fast results, and ask a professional before making big changes.
When to talk to a health professional
If your result is below 18.5 or above 25, if your weight changed quickly without explanation, or if you have conditions such as diabetes, high blood pressure or heart problems, talk to a doctor or nutritionist. They can interpret your BMI together with your history and suggest a safe plan.
Frequently asked questions
Is a BMI calculator accurate? It does the math correctly, but the BMI itself is a simple estimate that ignores muscle, bone and fat distribution.
How often should I check my BMI? Once a month is enough for most adults. Checking every day only shows normal daily weight changes.
Does the same BMI apply to men and women? Yes, the adult ranges are the same, although body composition differs between sexes.
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