BMI Calculator
Adjust the inputs below. Results update as you type.
How it works
Body mass index (BMI) is a height-and-weight screening ratio used in public-health categories for adults. It is quick to compute and useful for population context, but it is not a direct measure of body fat, fitness, or individual disease risk. Muscle mass, age, sex, ethnicity, and fat distribution all limit how far you should push a single number.
Enter height and weight in metric or U.S. units. The calculator reports BMI and the standard adult bands (underweight through Class III obesity where applicable). Athletes and people with high muscle mass may land in a higher BMI category without excess adiposity; older adults may have health risks at lower BMI than charts suggest.
Use BMI as a starting conversation with other metrics—waist measures, body-fat estimates, clinical labs, and how you feel day to day. It does not diagnose conditions and is not calibrated as a pediatric clinical tool on this page. If results are extreme or conflict with symptoms, seek qualified medical guidance rather than adjusting diet or training from BMI alone.
Input guidance
- Use a recent measured weight and accurate height.
- Adult category charts do not replace pediatric clinical assessment.
- Interpret BMI with body composition and medical context, not alone.
The formula
BMI = weight (kg) ÷ height (m)², or 703 × weight (lb) ÷ height (in)². Standard adult categories: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese.
Worked example
A person 1.75 m tall weighing 70 kg has BMI = 70 ÷ (1.75)² = 70 ÷ 3.06 = 22.9, which falls in the normal range.
More examples to test
- 5'10" and 180 lb: locate the adult category and neighboring band boundaries.
- Same BMI with high muscle mass: note why category alone can mislead.
How to interpret results
BMI is a screening ratio. Combine it with waist, fitness, labs, and clinician guidance before changing health plans.
When this can be inaccurate
Does not measure body fat directly; athletes, older adults, and some ethnic groups may be misclassified by BMI alone.
Change history
- July 2026: Added Class I–III framing and adult screening limitations.
- June 2026: BMI bands and unit handling reviewed.
Site-wide corrections also appear on the corrections log.
Track calories, macros, and fitness progress
General wellness resource.
Frequently asked questions
Is BMI accurate for everyone?+
No. BMI does not distinguish muscle from fat, so athletes can read as overweight and some people with low muscle can read as normal despite high body fat.
What is a healthy BMI?+
For most adults, 18.5–24.9 is considered the healthy range, but it is a screening tool, not a diagnosis — context and other measures matter.
Does BMI work for children?+
Children use age- and sex-specific BMI percentiles, not the fixed adult categories, because their body composition changes as they grow.
Can this calculator diagnose a condition?+
No. It is a screening and education tool only, not a clinical diagnosis.
When should I seek professional advice?+
Seek professional advice when results are extreme, persistent, or conflict with symptoms, goals, or prior medical guidance.
Guided next steps
Want the full workflow? Use this calculator inside a step-by-step guide.
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