BMI is a screening estimate for adults age 20 and older. It is not a diagnosis or a substitute for professional medical advice. BMI does not directly measure body fat and should be considered alongside other health factors. If you have health questions, speak with a qualified healthcare provider.
What the result explains
What This Calculator Provides
This calculator estimates body mass index (BMI) for adults age 20 and older from height and weight. Choose metric or imperial units and the tool converts measurements before applying the same formula. The result includes the BMI value, the general adult CDC category, and the weight range corresponding to BMI 18.5 through 24.9 at the entered height. BMI can help describe weight relative to height across populations, but it does not measure body fat or diagnose an individual health condition.
- BMI to one decimal place
- general adult BMI category
- height-specific BMI 18.5–24.9 weight range
How to Use This Calculator
- Enter the known valuesUse the labeled fields and units shown in the calculator. Correct any validation message before continuing.
- Review the resultRead the main answer together with its breakdown, formula, rounding, and assumptions.
- Copy and verifyCopy the result when available, then check important decisions against the relevant record, institution, or professional.
Method
Formula and Calculation Method
Metric BMI formula
BMI = weight (kg) ÷ height² (m²).
- Convert centimeters to meters by dividing by 100.
- Square the height before dividing the weight.
A person who is 175 cm tall is 1.75 m tall, so the denominator is 1.75 × 1.75.
Imperial BMI formula
BMI = 703 × weight in pounds ÷ (height in inches)²
- Total inches = feet × 12 + remaining inches.
- The factor 703 adapts pounds and inches to the metric definition.
The calculator converts pounds and total inches using exact unit definitions before evaluating BMI.
Worked from input to answer
Worked Examples
Published example: For an adult who weighs 70 kg and is 175 cm tall, BMI is 22.9.
Metric example: 70 kg and 175 cm
- Height = 175 ÷ 100 = 1.75 m
- BMI = 70 ÷ (1.75 × 1.75)
Result: BMI = 22.9, which falls in the general adult healthy-weight category.
Imperial example: 180 lb and 5 ft 10 in
- Total height = (5 × 12) + 10 = 70 inches
- BMI = 703 × 180 ÷ 70²
Result: BMI = 25.8, which falls in the general adult overweight category.
The Measurements Behind the Number
BMI is only as good as the two figures you feed it, and those usually arrive in mismatched units. Converting kilograms to pounds or centimeters to inches first avoids the most common mistake, which is mixing a metric weight with an imperial height.
If you work in stone, or your scale and your doctor disagree about units, the weight converter and the height converter handle every combination. To read a change over time honestly, expressing it as a percentage says more than the raw difference does.
What BMI measures
BMI relates body weight to the square of height. It is useful as a consistent screening measure, particularly in population research, because it needs only two measurements. It is not a direct body-fat measurement and does not describe fat distribution, muscle mass, bone density, fitness, blood pressure, or laboratory results.
Adult BMI categories
The following ranges are the CDC categories for adults age 20 and older. A category is context for a screening number, not a diagnosis.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to below 25 | Healthy weight |
| 25 to below 30 | Overweight |
| 30 or above | Obesity |
How to interpret the result
Treat BMI as one starting point alongside age, health history, body composition, and advice from a qualified clinician. The adult cutoffs are not the correct interpretation method for children and teenagers, whose BMI is evaluated by age- and sex-specific percentiles.
Practical Uses
- Checking an adult screening value before a routine appointment
- Comparing metric and imperial BMI calculations
- Understanding how a height or weight change affects the formula
- Learning the adult category boundaries used in public-health reporting
Assumptions
- The person is an adult age 20 or older.
- Height and weight are measured accurately without unit mix-ups.
- The standard adult CDC category ranges are being used.
Important Limitations
- BMI does not directly measure body fat or diagnose health.
- It can be less representative for very muscular people, during pregnancy, and in some older adults or people with body-composition differences.
- Children and adolescents require BMI-for-age interpretation, which this calculator does not provide.
Sources and References
- CDC: Adult BMI CategoriesAdult category ranges and screening interpretation.
Frequently asked questions
Common questions about BMI
Everything you need to know about using our BMI calculator.
Is BMI a diagnosis?
No. BMI is a screening measure. Individual health assessment may include body composition, medical history, examination, and other measures.
Does the calculator support pounds and feet?
Yes. Choose Imperial, then enter pounds plus feet and inches. Inches must be less than 12.
Why is height squared in the BMI formula?
Squaring height is part of the BMI definition and scales weight relative to body size more usefully than dividing by height alone.
Can I use adult BMI categories for a child?
No. Children and teens use age- and sex-specific BMI percentiles, not the fixed adult cutoffs shown here.
Why can a muscular person have a high BMI?
BMI uses total weight and cannot distinguish muscle from fat, so greater muscle mass can raise the result.