BMI Calculator
Understand your body composition with our simple Body Mass Index tool.
Your Result
“BMI is only one indicator and does not directly measure body fat or overall health.”
BMI Limitations: BMI is a useful screening tool but does not diagnose body fatness or health. It does not differentiate between muscle and fat.
- Athletes may have a high BMI due to muscle mass.
- Older adults may have more body fat than younger adults with the same BMI.
Always consult a healthcare provider for a complete health assessment.
How to Use This Calculator
- 1 Choose your system: Toggle between Metric (kg/cm) and Imperial (lbs/ft) units using the tabs at the top of the calculator.
- 2 Input measurements: Enter your accurate weight and height in the respective fields.
- 3 Add details (Optional): Providing age and gender helps contextualize the data, though the core BMI calculation relies strictly on height and weight.
- 4 View results: Click "Calculate BMI" to see your score, health category, and estimated ideal weight range.
Underweight
< 18.5
Normal
18.5 - 24.9
Overweight
25.0 - 29.9
How is BMI Calculated?
The Body Mass Index (BMI) is calculated by dividing a person's weight in kilograms by the square of their height in meters. It provides a simple numeric measure of a person's thickness or thinness, allowing health professionals to discuss weight problems more objectively.
Metric Units
BMI = kg / m²
Imperial Units
BMI = 703 × lbs / in²
BMI Categories Table
| BMI category | BMI range (kg/m²) | What it means |
|---|---|---|
| Underweight | < 18.5 | May indicate undernutrition or illness |
| Healthy weight | 18.5 – 24.9 | Typical range for most adults |
| Overweight | 25.0 – 29.9 | Higher than recommended weight |
| Obesity (Class I) | 30.0 – 34.9 | Increased health risks |
| Obesity (Class II) | 35.0 – 39.9 | High health risks |
| Obesity (Class III) | ≥ 40.0 | Very high health risks |
Note: Based on authoritative sources like the CDC, NHS, and WHO, which all use very similar cut-offs for adults.
Common BMI Examples
Height: 180 cm
Weight: 75 kg
Result
BMI 23.1 (Normal)
Height: 165 cm
Weight: 85 kg
Result
BMI 31.2 (Obese)
Height: 175 cm
Weight: 50 kg
Result
BMI 16.3 (Underweight)
Frequently asked questions (FAQ)
What is the Body Mass Index (BMI) and how does this tool work?
Body Mass Index is a simple, free screening system that uses a standard formula (kg/m2) to estimate body fat. Our online calculator is a lightweight and user-friendly tool designed to measure your mass relative to your height. When you use this metric, it helps determine if you fall within a widely accepted weight range.
Which category on the BMI scale is considered healthy?
For most adults, a value between 18.5 and 24.9 is generally considered healthy. The calculator will evaluate your data and place you into a specific category:
- Below 18.5: Underweight
- 18.5 – 24.9: Normal/Healthy Weight
- 25.0 – 29.9: Overweight
- 30.0 and above: Obese
Is this interactive method reliable for athletes?
Not always. While this is a fast and intuitive way to analyze general health, it may not be comprehensive for everyone. The index does not distinguish between muscle and fat. Because muscle is denser, athletes may compare poorly on the scale—appearing overweight even with low body fat. In these cases, a more customizable assessment of body composition is needed to be accurate.
How does age adjust the BMI calculation?
Standard BMI ranges are static for adults (20+), but the interpretation is dynamic for younger people. For children and teens, we must interpret the result differently. We compare their numbers against growth charts (percentiles) relative to their age and gender to ensure the assessment is correct.
Why does the user need to input gender?
Although the mathematical formula is the same, the interface asks you to enter gender because men and women often have different body fat distributions. To assess health risks properly, it helps to know that at the same BMI unit, women typically carry more body fat than men.
How do I determine the health risks of a high BMI?
If the system shows you are in the overweight or obese category, it is time to evaluate potential risks. A high BMI is a strong indicator that can help you and your doctor track the likelihood of developing chronic conditions such as type 2 diabetes, heart disease, stroke, and sleep apnea.
Are there risks to having a low value?
Yes. If the display shows a result below 18.5, it suggests you are underweight. This metric can signal health issues such as a weakened immune system, osteoporosis (fragile bones), anemia, or fertility issues. You should measure your progress carefully if you fall into this zone.
Why measure waist size if I already have my BMI result?
BMI provides a general estimate, but a waist measurement offers a visual check on where you carry weight. This is crucial because excess belly fat (visceral fat) is a more dangerous health risk than fat stored on the hips. Combining waist data with your BMI provides a more responsive and accurate picture of your heart health.
Can pregnant women use this to track weight?
No. This online tool is not designed to monitor pregnancy weight gain. Pregnant women require a specific weight gain plan to ensure the baby is healthy. You should consult a doctor to determine the right goals rather than relying on a standard BMI assessment.
The interface displays my result; what should I do next?
Remember that BMI is a screening tool, not a medical diagnosis.
- If your result is outside the "Normal" range: Use the data as a starting point to consult a healthcare provider. They can perform a full check using other metrics (like blood pressure) to create a customizable health plan.
- If your result is Normal: Continue to maintain a balanced diet and use this interactive page to periodically calculate and track your stats.