BMI Calculator
Use the free HealthFling BMI Calculator to estimate your body mass index from your height and weight. Choose metric (cm/kg) or US/UK-friendly imperial units (ft/in and lb), then get your BMI and adult screening category instantly.
Calculate Your BMI
Your BMI Result
What Is BMI?
Body mass index (BMI) compares weight with height. For adults, it is commonly used as a quick screening measure for weight status. BMI does not directly measure body fat and should be considered alongside other information about health.
A simple adult BMI screening tool
The HealthFling BMI Calculator gives an instant adult BMI result using either metric or US/imperial measurements. Use the result as a screening reference, then consider your wider health, lifestyle, activity and individual circumstances.
How Is BMI Calculated?
The metric formula is weight in kilograms ÷ height in metres². With pounds and inches, the formula is 703 × weight in pounds ÷ height in inches². This HealthFling calculator performs the conversion automatically.
Adult BMI Categories
| BMI | Adult screening category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0–34.9 | Obesity — Class 1 |
| 35.0–39.9 | Obesity — Class 2 |
| 40.0 or above | Obesity — Class 3 |
BMI Limitations You Should Know
BMI can sometimes classify muscular people at a higher BMI even when they do not have a high level of body fat. Interpretation can also require additional context for different populations. For example, NHS guidance notes that some ethnic groups can develop weight-related health risks at lower BMI levels. If you are concerned about your result, discuss it with a qualified healthcare professional.
Who Is This BMI Calculator For?
This calculator uses standard adult BMI categories and is intended for adults aged 20 or older. Children and teenagers require age- and sex-specific BMI assessment rather than the adult categories used here. Pregnancy and some medical circumstances can also make a standard adult BMI result less useful, so professional advice may be more appropriate.
5 Powerful BMI Insights to Keep in Mind
- BMI is a screening number, not a diagnosis. It is useful for broad adult weight-status screening but cannot describe your complete health.
- Muscle can affect interpretation. A person with more muscle may have a higher BMI even when body-fat levels are not high.
- Waist size and other measures can add context. Blood pressure, laboratory results, activity, medical history and body composition may provide additional information.
- Small sustainable habits matter more than chasing one number. Nutrition, movement, sleep and consistency are usually more practical daily targets than repeatedly checking BMI.
- Professional advice can be useful when a result raises concerns. This is especially important when there are medical conditions, pregnancy, unexpected weight changes or other health symptoms.
Useful HealthFling Tools
For movement planning, visit the HealthFling Steps Calculator. You can also use Build My Free Plan or continue to the HealthFling Journey for practical habit-building.
Frequently Asked Questions
What is a healthy BMI for adults?
Using standard adult categories, a BMI from 18.5 to below 25 is described as the healthy-weight range. BMI still needs to be interpreted in context.
Is BMI the same as body-fat percentage?
No. BMI is calculated from height and weight and does not directly measure body-fat percentage.
Can athletes have a high BMI?
Yes. Because BMI does not distinguish muscle from fat, a muscular person may have a higher BMI without having a high amount of body fat.
Can I use this calculator for a child or teenager?
No. This tool uses adult categories for ages 20 and older. Children and teens need BMI-for-age assessment.
Should I make health decisions based only on BMI?
No. BMI is a screening measure. Consider it with other health information and seek professional advice when appropriate.
HealthFling uses established public-health guidance for this educational tool. Read the CDC adult BMI categories, CDC explanation of BMI, and NHS guidance on BMI and its limitations.
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