BMI Calculator
Calculate BMI online with international and Asia-Pacific classifications, healthy range targets, WHtR checks, and exportable charts for metric or imperial inputs.Estimated BMI
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| BMI range | Category | Copy |
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1. The web tool provided is for general informational purposes only and should not be considered as professional advice.
2. We do not guarantee the accuracy, completeness, or reliability of the tool.
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Introduction:
Body Mass Index estimates relative weight for height and is commonly used to screen broad weight categories. It pairs well with waist‑to‑height ratio for a quick check of central adiposity. These indices are simple snapshots that help track trends over time rather than precise measures of health.
Enter weight and height in either metric or imperial units to see BMI, its category band, BMI Prime, a healthy weight range for your height, and optional waist‑to‑height ratio when you provide a waist reading. Select the classification preset that fits your population and use the target BMI slider to map a personalised goal weight. Results update instantly as you adjust units or values.
Treat boundaries with caution. A small change near a threshold can flip the label without reflecting a meaningful difference. Age, sex, ethnicity, pregnancy, and athletic body composition can shift interpretation.
This tool provides informational estimates and does not substitute professional advice.
Technical Details
Body Mass Index (BMI) is defined as mass divided by height squared. BMI Prime expresses BMI relative to the upper bound of the healthy band (25 kg/m²), and a healthy weight range derives from 18.5–24.9 kg/m² at your height. Waist‑to‑height ratio (WHtR) is waist circumference divided by height and offers a simple central adiposity check. The tool includes WHO, Asia-Pacific, and NIH/CDC adult reference tables so you can compare interpretations across regions.
| Symbol | Meaning | Unit/Datatype | Source |
|---|---|---|---|
| Body mass | kg | Input (kg or lb → kg) | |
| Stature | m | Input (cm/m/in → m) | |
| Waist circumference | m | Input (cm/in → m) | |
| Body Mass Index | kg/m² | Derived | |
| BMI Prime (BMI/25) | unitless | Derived | |
| Waist‑to‑height ratio | unitless | Derived |
Worked example
Weight 70 kg, height 1.70 m, waist 80 cm.
Interpretation: BMI in the “Normal” band; WHtR around 0.47 is typically considered acceptable for adults.
BMI bands (adults)
| Category | Lower | Upper | Implication |
|---|---|---|---|
| Severely Underweight | 0 | 16.49 | Clinical concern; seek guidance. |
| Underweight | 16.5 | 18.49 | Below recommended range. |
| Normal | 18.5 | 24.9 | Typical healthy band. |
| Overweight | 25 | 29.9 | Elevated risk indicator. |
| Obese I | 30 | 34.9 | Increased clinical risk. |
| Obese II | 35 | 39.9 | High clinical risk. |
| Obese III | 40 | 100 | Very high clinical risk. |
Units, precision, and rounding
- Weight: kg or lb; height: cm, m, or in; waist: cm or in.
- Internal math converts to kg and m; displayed BMI uses one decimal, BMI Prime three decimals, WHtR three decimals.
- Healthy weight range uses 18.5–24.9 kg/m² with one‑decimal rounding.
Input & validation
| Field | Type | Accepted values | Notes | Placeholder |
|---|---|---|---|---|
| weight | number | > 0 | kg or lb; converts to kg | 70 |
| height | number | > 0 | cm/m/in; converts to m | 170 |
| waist | number | > 0 | Optional; cm/in → m for WHtR | 80 |
| age | number | 0–120 | Optional; not used in math | — |
| sex | enum | male/female | Optional; not used in math | — |
I/O formats
| Input | Accepted Families | Output | Encoding/Precision |
|---|---|---|---|
| Weight, height, waist | Numbers with units | BMI, Prime, WHtR | 1–3 decimals as noted |
| — | — | Healthy weight range | One decimal; kg and lb |
| — | — | CSV/JSON exports | Plain CSV; UTF‑8 JSON |
Privacy & compliance
Calculations run in your browser; no data is sent to a server. These outputs are estimates and not medical advice.
How‑to Guide
- Enter Weight and pick kg or lb.
- Enter Height and pick cm, m, or in.
- Select a BMI classification preset or leave the WHO default.
- Adjust the Target BMI slider to preview an exact goal weight.
- Optional: add Waist to see WHtR.
- Review BMI, category, BMI Prime, and healthy range; copy or download if needed.
Example: 70 kg, 170 cm → BMI ≈ 24.2 (Normal), Prime ≈ 0.968; waist 80 cm → WHtR ≈ 0.471.
Assumptions & limitations
- Indices screen broad categories; they do not diagnose health.
- Muscular, pregnant, growing, or older individuals may not fit BMI bands well.
- WHtR is available only when both waist and height are valid.
- Rounding at one decimal can shift labels at boundaries.
Edge cases & error sources
- Zero or negative height/weight suppresses results.
- Mixed units without switching selectors yield incorrect values.
- Very small heights or extreme weights can exceed typical adult ranges.
- Locale formatting affects displayed separators; exports keep plain ASCII digits.
FAQ
Is my data stored?
No. Inputs and outputs stay on your device; exports are created locally.
Can I use pounds and inches?
Yes. The app converts lb→kg and in→m before calculation; results display consistently.
Which number should I watch?
Track BMI trend over time and consider WHtR when central fat is a concern. Use the healthy range as a planning guide.
Does BMI apply to athletes?
BMI can misclassify very muscular people; pair it with performance markers and body composition measures when available.