What Is a BMI Calculator?

A BMI calculator is a simple tool that estimates your Body Mass Index using your height and weight. BMI is one of the most widely used screening measures for assessing whether your weight falls within a healthy range for your height. Use the calculator above to get your BMI, your category, and a healthy weight range for your height in seconds.

How Is BMI Calculated?

BMI is calculated by dividing your weight in kilograms by your height in meters, squared. In imperial units, it’s your weight in pounds divided by your height in inches squared, multiplied by 703. This gives a single number that places you into one of four standard categories: underweight, normal weight, overweight, or obese.

Understanding Your BMI Result

• Below 18.5 — Underweight
• 18.5 to 24.9 — Normal weight
• 25 to 29.9 — Overweight
• 30 and above — Obese

These ranges are based on World Health Organization guidelines and apply to most adults. If your BMI falls outside the normal range, it’s worth discussing with a healthcare provider rather than making changes based on this number alone.

Why BMI Isn’t the Whole Picture

BMI is a useful starting point, but it has real limitations. It doesn’t distinguish between muscle and fat, so athletes and people with higher muscle mass can show a higher BMI without carrying excess body fat. It also doesn’t account for where fat is distributed on the body, which matters for certain health risks. Age, sex, and bone density can shift what counts as a healthy range for one person versus another.

For a fuller picture of your health, consider pairing your BMI result with a waist circumference measurement, a body fat percentage reading, or a conversation with a doctor. Think of BMI as a quick screening tool — a place to start, not a diagnosis.

How to Use This BMI Calculator

Choose your preferred unit system — metric or imperial — using the toggle above. Enter your height and weight, and optionally your age. Click “Calculate BMI” to see your result, your category on the scale, and the healthy weight range for your height. Your data stays in your browser and isn’t stored or sent anywhere.

Frequently Asked Questions

Is BMI accurate for everyone?

No. BMI works reasonably well as a general screening tool for most adults, but it’s less reliable for athletes, older adults, pregnant women, and growing children, since it can’t tell the difference between muscle, fat, and bone.

What’s a healthy BMI range?

For most adults, a BMI between 18.5 and 24.9 is considered within the healthy range. This calculator shows you the exact healthy weight range in kilograms or pounds based on your specific height.

Can I use this BMI calculator for my child?

This calculator is built for adults. Children and teens are assessed using age- and sex-specific BMI percentiles rather than the fixed adult categories shown here, so a pediatric growth chart is the more accurate tool for anyone under 18.