BMI Calculator
Calculate your Body Mass Index and understand your BMI category based on your height and weight.
- Metric & US Units
- Healthy Weight Range
- PDF Report
- Works on Mobile
Calculate Your BMI
Choose any height & weight unit combination.
BMI Calculator is a free online tool that helps you calculate your Body Mass Index using your height and weight. Simply enter your measurements in metric or US units, and our BMI Calculator instantly shows your BMI value, BMI category, and healthy weight range. The entire calculation runs in your browser — no signup, no data sent to any server.
Table of Contents
What is BMI? (Body Mass Index Explained)
Body Mass Index (BMI) is a simple screening measure that uses your height and weight to estimate whether your body weight falls within a healthy range. It is one of the most widely used health indicators worldwide because it is quick, free and requires no special equipment — just your height and weight.
BMI is often used by doctors, nutritionists and health organizations as a first step to identify potential weight-related health risks. However, it is important to understand that BMI is not a medical diagnosis. It is a general screening tool, not a direct measure of body fat or overall health.
Why BMI is Used as a Screening Tool
- It is fast and free to calculate
- It applies the same formula to all adults
- It gives a general idea of whether weight may be a health concern
- It is useful for tracking weight trends over time
How to Use the BMI Calculator
Our free online BMI Calculator is designed to give you an instant result in any unit combination. You can mix and match metric and US units — for example, feet with kilograms, or centimeters with pounds.
Step 1 – Enter Your Height
Choose cm for centimeters, or ft + in for feet and inches. Enter your height in the selected unit.
Step 2 – Enter Your Weight
Choose kg for kilograms or lb for pounds. Enter your current weight.
Step 3 – Click Calculate
Press the Calculate BMI button. You’ll instantly see:
- Your BMI value
- Your BMI category (Underweight, Healthy Weight, Overweight or Obesity)
- Your healthy weight range for your height
- An option to download a PDF report
The calculator also supports an optional age and gender input. Note that for users under 18, adult BMI categories are not used, because BMI-for-age requires specialized growth charts.
How BMI is Calculated (The BMI Formula)
BMI is calculated using a simple mathematical formula. The formula differs slightly between the metric system and the US customary system.
Metric BMI Formula
BMI = Weight (kg) ÷ Height² (m)
To use this formula, convert your height from centimeters to meters by dividing by 100. Then square that number and divide your weight by it.
US Unit BMI Formula
BMI = 703 × Weight (lb) ÷ Height² (in)
The number 703 is a conversion factor that adjusts the formula for pounds and inches.
Example Calculation
Example 1 — Metric:
- Height: 175 cm = 1.75 m
- Weight: 70 kg
- BMI = 70 ÷ (1.75 × 1.75) = 22.9
Example 2 — US Units:
- Height: 5 ft 9 in = 69 inches
- Weight: 154 lb
- BMI = 703 × 154 ÷ (69 × 69) = 22.7
A BMI of 22.9 or 22.7 both fall into the Healthy Weight category.
Adult BMI Categories (Chart)
For adults aged 18 and older, the World Health Organization (WHO) uses the following standard BMI categories:
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy Weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Obesity is sometimes further divided into:
- Class 1: 30.0 – 34.9
- Class 2: 35.0 – 39.9
- Class 3: 40.0 and above
These ranges are based on population-level data and are not intended as a diagnosis for any individual.
Underweight (Below 18.5)
Being underweight may indicate nutritional deficiencies, weakened immunity or underlying health conditions. If your BMI is below 18.5, consider speaking with a healthcare professional.
Healthy Weight (18.5 – 24.9)
This range is associated with the lowest risk of weight-related health problems for most adults.
Overweight (25.0 – 29.9)
Being in the overweight range may increase the risk of certain health conditions, but it does not automatically mean you are unhealthy. Factors like muscle mass, activity level and genetics all matter.
Obesity (30.0 and above)
Obesity is associated with a higher risk of several health conditions. However, BMI alone cannot determine your overall health — a proper evaluation by a healthcare professional is important.
What is a Healthy Weight Range?
A healthy weight range is the range of body weights that corresponds to a BMI of 18.5 to 24.9 for your specific height. Our BMI Calculator automatically estimates this range and displays it based on the unit system you selected.
Example: For someone 175 cm (5 ft 9 in) tall, the healthy weight range is approximately:
- Metric: 56.7 kg – 76.3 kg
- US: 125 lb – 168 lb
This range is a general guideline, not a strict target. Your ideal weight can vary based on age, muscle mass, body composition and overall health.
BMI for Children and Teenagers (Under 18)
BMI is interpreted differently for children and teenagers. This is because body composition changes significantly during growth, and the amount of body fat naturally varies by age and sex.
For people under 18, BMI should be assessed using age- and sex-specific BMI-for-age growth charts (also called BMI percentile). These charts compare a child’s BMI to others of the same age and sex.
Important: Our BMI Calculator does not provide a pediatric BMI category. If you are under 18, use the calculator to find your BMI value, then consult a pediatrician or use a dedicated BMI-for-age percentile tool.
Limitations of BMI – What It Doesn’t Measure
BMI is a useful screening tool, but it has important limitations. It does not:
- Distinguish between muscle and fat. Athletes and very muscular people often have a high BMI without excess body fat.
- Account for body fat distribution. Fat stored around the waist is more concerning than fat stored elsewhere.
- Reflect differences by age, sex or ethnicity. Body composition varies across populations.
- Work well for certain groups. Older adults, pregnant people, and very tall or very short individuals may not be accurately represented.
- Measure overall health. Fitness, nutrition, blood pressure, cholesterol and genetics all play a role in health.
Bottom line: BMI is a starting point for understanding your weight, not a complete picture of your health.
Frequently Asked Questions (FAQ)
What is a healthy BMI for adults?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy weight range.
How do I calculate BMI in kg and cm?
Divide your weight in kilograms by your height in meters squared: BMI = kg ÷ (m × m).
Can I use pounds and feet with this calculator?
Yes. Our calculator supports both metric and US units, and you can even mix them (for example, feet with kilograms).
Is BMI the same for men and women?
The formula is the same, but body composition differs, so BMI may not reflect health equally for everyone.
Can BMI be used for children?
No — for children and teens under 18, BMI should be interpreted using age- and sex-specific growth charts, not adult BMI categories.
How accurate is BMI?
BMI is a screening tool, not a diagnostic test. It is accurate on a population level but may not reflect an individual’s health perfectly.
Does BMI measure body fat?
No. BMI only uses height and weight and does not directly measure body fat.
What is a healthy weight range?
It is the weight range that corresponds to a BMI of 18.5–24.9 for your height.
Is this BMI Calculator free?
Yes, our BMI Calculator is completely free and requires no registration.
Can I download my BMI result?
Yes, you can download a PDF report that includes your BMI, category and healthy weight range.
Try Our BMI Calculator Now
Ready to check your Body Mass Index? Scroll up and use our free BMI Calculator — it takes just a few seconds. Enter your height and weight, click Calculate, and get your BMI value, category and healthy weight range instantly.