BMI Calculator
Calculate your Body Mass Index (BMI) instantly with our free online calculator. Get your weight category, health guidance, and understand what your BMI means for your health.
What is BMI?
BMI (Body Mass Index) is a numerical measure of body fat based on weight relative to height. It's widely used to categorize individuals as underweight, normal weight, overweight, or obese. Formula: BMI = weight (kg) ÷ height² (m²).
What is a healthy BMI range?
A healthy BMI ranges from 18.5 to 24.9. Below 18.5 is considered underweight, 25-29.9 is overweight, and 30 or above is classified as obese. This range applies to most adults aged 18-65.
Is BMI accurate for everyone?
BMI is a useful screening tool but has limitations. It doesn't distinguish between muscle and fat mass, so athletes may have high BMI despite being healthy. It may also be less accurate for pregnant women, elderly people, and growing children.
How do I calculate BMI in imperial units?
For imperial units, use this formula: BMI = (weight in pounds × 703) ÷ (height in inches)². Alternatively, convert to metric first: 1 pound = 0.4536 kg, 1 inch = 0.0254 meters.
What are the BMI categories?
BMI categories are: Underweight (below 18.5), Normal weight (18.5-24.9), Overweight (25-29.9), Obese Class I (30-34.9), Obese Class II (35-39.9), and Obese Class III (40 or higher).
What are the health risks of high BMI?
High BMI (overweight and obesity) increases risk of heart disease, type 2 diabetes, high blood pressure, stroke, certain cancers, sleep apnea, and osteoarthritis. Maintaining a healthy weight reduces these risks.
What are the health risks of low BMI?
Low BMI (underweight) can lead to malnutrition, weakened immune system, osteoporosis, anemia, fertility issues, and increased risk of complications from surgery or illness.
How often should I check my BMI?
For general health monitoring, checking BMI once a month is sufficient. If you're actively trying to lose or gain weight, weekly checks can help track progress. Remember BMI is just one indicator of health.
What is the BMI formula?
The BMI formula is: BMI = weight (kg) ÷ height² (m²). For imperial units: BMI = (weight in pounds × 703) ÷ (height in inches)². The result is the same regardless of units used.
Can BMI be used for children and teenagers?
BMI can be used for children and teens aged 2-19, but it's interpreted differently using age and sex-specific percentile charts. A pediatric BMI calculator should be used instead of adult charts.
How to Use BMI Calculator
Calculate your Body Mass Index in seconds and see which weight category it falls into. Everything is computed in your browser, so your height and weight are never sent anywhere.
- Choose Metric or Imperial next to Unit:, depending on the measurements you are used to.
- In Metric mode, type your height into the Height (cm) box and your weight into the Weight (kg) box.
- In Imperial mode, fill in Height (ft) and Height (in) separately, then enter your weight in Weight (lbs).
- Read your BMI score and its category — underweight, normal, overweight, or obese — shown as soon as you finish typing.
- Use the accompanying health guidance to decide whether the result warrants professional advice.
BMI does not distinguish muscle from fat, so athletic people often land in the overweight band despite low body fat.
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