Health Calculator · Adults 20+
BMI Calculator
Body mass index (BMI) compares weight with height. This adult BMI calculator is for people aged 20 and older. Use centimeters and kilograms or feet, inches and pounds to explore BMI categories, reference weight ranges, weight comparisons and dated trends. Results are informational, not a medical assessment.
BMI inputs
Sample measurements are prefilled. Replace them with your own values. No data is uploaded or stored by this calculator.
Changing region resets the sample and optional entries. Changing units converts entered measurements, rounded to two input decimals; this may slightly affect results near a classification boundary.
Whole number of feet
0 up to, but below, 12 inches
Use a period (.) as decimal separator, up to two places
Your BMI results
Enter valid measurements to see your results. Results are hidden while the inputs are invalid.
BMI Explorer
Alternative weight scenario
Compare an imagined weight at the same height. This is mathematical exploration, not a recommended weight.
Reverse BMI → weight
To explore a target BMI, enter a reference value to find the corresponding weight at your height. This is a mathematical conversion, not a recommendation to reach that BMI or weight.
Previous weight comparison
Compare your current BMI and weight to a previous measurement. Lower or higher weight is not automatically labeled healthier.
Dated weight and BMI history
Manually enter up to 50 optional records dated YYYY-MM-DD, all using your current entered height. They stay only in this page session, with no automatic saving. Dates need not be before today. The current undated weight is not inserted into the chart.
No dated measurements yet. Add two or more records to see historical trends.
Formula and calculation assumptions
| Measure | Formula |
|---|---|
| BMI | Weight (kg) ÷ Height (m)² |
| BMI Prime | BMI ÷ 25 |
| Ponderal Index | Weight (kg) ÷ Height (m)³ |
| Mosteller BSA | √[Height (cm) × Weight (kg) ÷ 3600] |
| BMI 18.5–below 25 reference | BMI boundary × Height (m)²; upper boundary excluded |
| Weight for selected BMI | Reference BMI × Height (m)² |
| Exact units | 1 in = 2.54 cm; 1 lb = 0.45359237 kg |
Worked example: 170 cm, 78 kg
BMI = 78 ÷ (1.70 × 1.70) ≈ 26.9896 (display 27.0, overweight). BMI Prime ≈ 1.0796; Ponderal Index ≈ 15.8762 kg/m³; Mosteller BSA ≈ 1.9192 m².
At 170 cm, the mathematical BMI reference weight interval is [53.465, 72.25) kg. The upper boundary is excluded. A hypothetical 72 kg corresponds to BMI ≈ 24.9135; a reference BMI of 22 corresponds to 63.58 kg. Neither number is a weight recommendation.
All category decisions use exact decimal-rational values, not rounded display numbers. The calculator uses the CDC 20+ category boundaries. BSA is estimated with the Mosteller formula. No child, pregnancy-specific, ethnicity-specific or personalized medical assessment is provided.
Sources: CDC adult BMI categories · NHLBI BMI calculator · Mosteller BSA reference.
Frequently Asked Questions
How do you calculate adult BMI?
Divide weight in kilograms by height in metres squared. US customary height and weight are converted using exact defined unit factors before calculation.
What BMI categories does this calculator use?
For adults aged 20 or older, the CDC categories are: underweight, below 18.5; healthy weight, 18.5 to below 25; overweight, 25 to below 30; obesity class 1, 30 to below 35; obesity class 2, 35 to below 40; and obesity class 3, 40 or above. Classification uses the unrounded BMI, not the one-decimal display.
What is the BMI reference weight interval for my height?
It is the weight interval mathematically corresponding to BMI 18.5 up to, but not including, BMI 25. The upper boundary is excluded. This is not an individual ideal-weight recommendation.
Why can the displayed BMI and category appear to disagree?
A BMI of 24.96 displays as 25.0 when rounded to one decimal place, but its exact value is still below 25, so it remains in the healthy-weight reference range.
Is BMI calculated differently for women and men?
No. For adults aged 20 or older, the standard CDC BMI formula and category cutoffs are the same for women and men. BMI does not distinguish muscle from fat, so the same BMI does not imply identical body composition or health. This calculator does not provide sex-specific body-fat estimates.
How are historical BMI readings calculated?
Each dated weight uses your currently entered height. Records are sorted by date and the current undated input is not automatically added to the history. One record is not considered a trend.
What are BMI Prime and the Ponderal Index?
BMI Prime is BMI divided by 25. The adult Ponderal Index displayed here is kilograms divided by metres cubed. Both are mathematical measures and do not correct every limitation of BMI.
What is body surface area (BSA)?
The optional BSA estimate uses the Mosteller formula: square root of (height in centimetres × weight in kilograms ÷ 3600). It is not a directly measured area and is not intended here for medication dosing.
Can I export or print my BMI results?
Export CSV downloads dated weights, BMI values and category codes in chronological order, using full numerical values rather than the rounded display. Print summary prints the current results and reference weight boundaries; the interactive explorer and history are excluded from that print summary.
Does this calculator provide a medical assessment?
No. BMI is a general screening measure and does not directly measure body fat or distinguish muscle from fat. This calculator excludes children, pregnancy-specific assessment, diagnoses, and personalized treatment advice.
Related Tools
For adults aged 20 or older. General educational measurements only. BMI is not a diagnosis, personal goal, treatment plan, or a replacement for qualified medical evaluation. Entered measurements and history remain in this browser tab's active component state and are not automatically stored or sent to a service by this tool.