BMI Calculator
Calculate adult BMI, understand the result visually, and learn what BMI can—and cannot—tell you.
Calculate your BMI
What BMI means
Body mass index (BMI) compares body weight with height. For adults, it is commonly used as a quick screening measure because it is simple and reproducible. It does not directly measure body fat, fitness, muscle mass, bone density or fat distribution.
Common adult reference ranges
| BMI | Classification |
|---|---|
| < 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0+ | Obesity range |
Important interpretation note
These are general adult screening thresholds. Some health authorities use additional subcategories or population-specific action points. A numerical category should not be treated as a diagnosis.
How BMI is calculated
Metric: BMI = weight (kg) ÷ height² (m)
Imperial: BMI = 703 × weight (lb) ÷ height² (in)
Worked example
A person weighing 70 kg and measuring 1.75 m has BMI = 70 ÷ (1.75 × 1.75) ≈ 22.9. The calculator uses the unrounded value internally and rounds the displayed BMI.
Healthy-weight range calculation
For an adult height, this page also shows the weights corresponding to BMI 18.5 through 24.9. That is a mathematical reference range based on BMI—not a personalized target weight.
Useful facts and limitations
BMI does not measure body fat
Two people can have the same BMI but very different proportions of muscle and body fat. This is one reason muscular athletes can receive a high BMI despite having relatively low body fat.
Age and life stage matter
Adult BMI cutoffs should not simply be applied to children and teenagers, who are normally interpreted using age- and sex-specific growth references. Pregnancy also changes the usefulness of ordinary adult BMI interpretation.
Population differences matter
Health risk can occur at different BMI levels in different populations. Country or population-specific clinical guidance may therefore use different action points from the general adult categories shown here.
Look beyond one number
Health assessment can also consider waist measurements, body composition, blood pressure, laboratory results, medical history, activity, nutrition and other factors. BMI is one piece of information.
BMI Prime and Ponderal Index
BMI Prime compares BMI with an upper reference value of 25: BMI Prime = BMI ÷ 25. A value of 1.00 therefore corresponds to BMI 25 under that reference.
Ponderal Index uses height cubed rather than height squared. MesraTools shows it as an additional mathematical index, not as a diagnosis or replacement for professional assessment.
Frequently asked questions
Can BMI tell me how much body fat I have?
No. BMI is calculated only from height and weight. It does not separate fat, muscle, bone or water.
Why can two BMI websites give slightly different results?
Differences can come from unit conversion, rounding, category boundaries or the reference standard used for interpretation. The underlying adult BMI formula itself is straightforward.
Should children use this adult BMI meter?
No. Children and teenagers require age- and sex-specific BMI-for-age interpretation. This MesraTools version intentionally limits its category meter to general adult interpretation rather than pretending the adult thresholds apply to children.
Is a “healthy BMI” proof that someone is healthy?
No. It is only a screening range. Health cannot be determined from BMI alone.
Does MesraTools store my measurements?
No. This calculator performs the calculation locally in the browser.
Related tools
Understand BMI Calculator
BMI Calculator converts your entered assumptions into a numerical estimate so you can understand the result, compare alternatives and make a more informed planning decision.
When this tool is useful
Use it for planning, comparison and what-if analysis before committing to a financial, time, health or everyday decision.
How to use it well
Enter the requested values carefully, confirm units and percentages, run the calculation, then review the headline result together with the breakdown and assumptions.
How to interpret the result
BMI is a screening ratio based on height and weight. It does not directly measure body fat, fitness, diagnosis or individual health status.
Practical suggestions
- Use the result as general information rather than a diagnosis.
- Consider age, body composition and clinical context where relevant.
- Speak with a qualified health professional for personal medical interpretation or concerns.
Example workflow
Example workflow: enter a representative bmi calculator input, run the tool, review the output, then change one important input and compare the difference.
Important limitations
BMI is a population-level screening measure with important individual limitations. This calculator does not provide diagnosis or medical advice.
Privacy: Where the page states that processing is browser-local, your entered content stays in the browser during normal processing. Any tool that requires server or third-party processing must disclose that separately.