Free BMI Calculator – Calculate Your Body Mass Index Online
By RapidTool Team · Last updated: September 2026
Body Mass Index (BMI) is a widely used screening tool that estimates whether a person has a healthy body weight for their height. Our free BMI calculator works with both metric (kilograms and centimeters) and imperial (pounds and inches/feet) units, giving you instant results with category classification and ideal weight range.
BMI Categories – What Does Your Score Mean?
| BMI RANGE | CATEGORY | HEALTH RISK |
|---|
| Below 18.5 | Underweight | Possible nutritional deficiency |
| 18.5 – 24.9 | Normal Weight | Lowest health risk |
| 25.0 – 29.9 | Overweight | Moderate health risk |
| 30.0 – 34.9 | Obese Class I | High health risk |
| 35.0 – 39.9 | Obese Class II | Very high health risk |
| 40.0 and above | Obese Class III | Extremely high health risk |
How Is BMI Calculated?
Metric formula: BMI = weight (kg) ÷ height² (m²)
Imperial formula: BMI = 703 × weight (lbs) ÷ height² (inches²)
For example, a person weighing 70 kg and 1.75 m tall has a BMI of: 70 ÷ (1.75 × 1.75) = 22.9, which falls in the Normal Weight category.
Frequently Asked Questions
Is BMI an accurate measure of health?
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat mass, so athletes with high muscle mass may have a high BMI without being unhealthy. BMI also doesn't account for age, sex, ethnicity, or body fat distribution. Always consult a healthcare professional for a full assessment.
What is a healthy BMI for adults?
For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, optimal ranges can vary by age and ethnicity. Some health organizations suggest different thresholds for Asian populations due to different body composition patterns.
Can children use this BMI calculator?
This calculator is designed for adults aged 18 and over. Children and teenagers should use age- and sex-specific BMI-for-age percentile charts, as their healthy weight ranges change with age and development. Consult a pediatrician for children's healthy weight assessment.
What is the ideal weight for my height?
Our calculator shows the ideal weight range for your height based on a healthy BMI of 18.5–24.9. For example, someone 5'7" tall has an ideal weight range of approximately 121–153 lbs (55–69 kg). This range is shown automatically after you calculate your BMI.
⚠️ Medical Disclaimer: This BMI calculator is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional before making any health decisions.