A useful first screening step
BMI summarizes weight relative to height and can help identify when more health or body-composition context may be useful.
Free BMI calculator for adults 20+
BMI Calculator for Adults (Body Mass Index)
Calculate adult BMI from height and weight in metric or imperial units. See your BMI category and compare it with standard adult ranges, then learn what this screening result can—and cannot—tell you.
Adults 20+
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Enter height and weight
Calculate your BMI
Adult screening result
Your BMI result
Your result will appear here
Enter your height and weight to see your BMI, adult category, BMI-equivalent healthy-weight range, and a short interpretation.
Body Mass Index—kg/m²
—
Category range—
BMI-equivalent healthy weight*—
Important: BMI is a screening measure. It does not directly measure body fat or distinguish fat mass from muscle and bone.
*Weight range corresponding to BMI 18.5–24.9 at your entered height. It is not an individualized target weight.
Adult BMI chart
BMI categories for adults age 20 and older
For adults 20 and older, standard BMI categories use the same cut points regardless of age, sex, or race. Class 1, 2, and 3 are subdivisions of the obesity range. These are screening categories and should be considered with other health information.
| BMI category | BMI range | Interpretation |
|---|---|---|
| Underweight | Below 18.5 | Below healthy-weight screening range |
| Healthy weight | 18.5 to <25 | Healthy-weight screening range |
| Overweight | 25 to <30 | Above healthy-weight screening range |
| Obesity — Class 1 | 30 to <35 | Class 1 obesity range |
| Obesity — Class 2 | 35 to <40 | Class 2 obesity range |
| Obesity — Class 3 | 40 or higher | Class 3 (severe obesity) range |
Reference: CDC Adult BMI Categories.
Interpret your result
What BMI can—and cannot—tell you
BMI is useful because it is quick, inexpensive, and consistent. For an individual, it is one screening measure—not a complete assessment of body composition or health.
Muscle and bone affect the number
BMI cannot distinguish fat from muscle or bone. Highly muscular people can have a higher BMI without having the same body-fat level as someone with a different body composition.
Other health measures add context
Waist circumference, blood pressure, medical history, physical examination, activity, and laboratory findings can provide a fuller picture.
BMI formula
How to calculate BMI in metric or imperial units
BMI compares body weight with height squared. The result is expressed as kg/m², including when you enter U.S. customary measurements.
BMI = weight (kg) ÷ height² (m²)Example: 70 kg ÷ (1.75 × 1.75) = 22.9
BMI = 703 × weight (lb) ÷ height² (in²)Example: 154 lb at 5 ft 9 in ≈ 22.7
Formula reference: CDC BMI Frequently Asked Questions.
Get a useful result
How to use this BMI calculator
Choose a unit system, enter your height and weight, then review the BMI value and adult category. Accurate measurements help make the estimate more useful.
Select metric or imperial units
Choose centimeters and kilograms, or feet/inches and pounds. Use the units shown beside each field.
Enter consistent measurements
Measure height without shoes and use a reliable scale on a firm, level surface. If tracking changes, measure under similar conditions.
Review the result in context
Compare your BMI with the adult chart, then consider other health information. BMI is a screening measure, not a diagnosis or personal target.
Tool guide
Understand and use the BMI Calculator
Use these tool-specific notes to understand the method, enter better data, interpret the output, and apply the result appropriately.
BMI Basics
BMI relates body mass to height squared. It is a simple adult screening measure for weight category, not a direct measure of body fat, muscle mass, or health status.
Measure Correctly
Use a current body weight and standing height without shoes. Consistent measurement conditions reduce avoidable variation when you track BMI over time.
BMI Formula
Metric BMI is kilograms divided by metres squared. Imperial entries are converted consistently before the same underlying relationship is applied.
Read the Category
Adult category cut points provide population-level screening context. Athletic build, pregnancy, edema, and other factors can make BMI less informative for an individual.
Frequently asked questions
BMI Calculator FAQs
Practical answers about this tool's inputs, method, results, limitations, and common real-world use.
What is a healthy BMI for adults?
For adults age 20 and older, the CDC healthy-weight BMI category is 18.5 to less than 25. BMI is a screening measure and should be considered with other health information.
Is BMI the same as body-fat percentage?
No. BMI uses height and weight only. It does not directly measure body fat or distinguish fat mass from muscle and bone mass.
Does age or sex change adult BMI categories?
For adults age 20 and older, standard BMI category cut points are used regardless of age or sex. Children and teens use age- and sex-specific BMI percentiles.
Can athletes have a high BMI because of muscle?
Yes. Because BMI cannot distinguish muscle from fat, a muscular adult may have a higher BMI even when body-fat levels are not high.
Should the BMI healthy-weight range be my goal weight?
Not automatically. The range shown here simply corresponds to BMI 18.5–24.9 at your height. Individual goals can depend on health history, body composition, performance needs, and professional guidance.
Why is this calculator for adults 20 and older?
Children and teens ages 2–19 are assessed with BMI-for-age percentiles because BMI is interpreted differently during growth and development.
Why is height squared in the BMI formula?
BMI scales body weight to height by dividing mass by height squared. It is an index designed for population screening; it is not a geometric model of individual body composition.
Will kilograms and pounds give the same BMI?
Yes when the height and weight are converted correctly. Metric and imperial inputs describe the same physical measurements, so they should produce the same BMI apart from display rounding.
How much can rounding change my BMI category?
Usually very little, but a value close to a category boundary can move when height or weight is rounded. Use reasonably precise measurements and interpret the unrounded calculation rather than chasing tiny changes.
Can water retention change BMI temporarily?
Yes. Short-term changes in fluid, glycogen, food mass, and hydration can change scale weight and therefore BMI without representing the same change in body fat. Trends are more useful than one isolated measurement.
Evidence & review
Sources and methodology
The formula, adult BMI thresholds, and screening guidance on this page are checked against current U.S. Centers for Disease Control and Prevention BMI resources.
- CDC — Adult BMI Categories
- CDC — Adult BMI Calculator
- CDC — BMI Frequently Asked Questions
- CDC — About Body Mass Index
Content reviewed: .
Health information disclaimer
This calculator is for general education and screening only. It does not diagnose a condition, directly measure body fat, or replace individualized medical advice. If your BMI result concerns you, or a health condition affects your nutrition, weight, or exercise plan, discuss your situation with a qualified healthcare professional.