Free BMI Calculator - Calculate Your Body Mass Index Online

Calculate your BMI (Body Mass Index) instantly with our free online calculator. Enter your height and weight to get your BMI score and category in seconds. Supports both metric (kg, cm) and imperial (lb, inches) units. No signup required.

BMI Calculator

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Your BMI result will appear here.

BMI Categories

BMI Range Category
Below 18.5 Underweight
18.5 – 24.9 Normal
25.0 – 29.9 Overweight
30.0 and above Obese

BMI is a screening tool, not a diagnosis. Consult a healthcare professional for personalized advice.

⚠️ Medical Disclaimer: This BMI calculator is for informational and educational purposes only. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding your health or weight.

What is BMI (Body Mass Index)?

Body Mass Index (BMI) is a numerical value derived from your height and weight. It serves as a screening tool to categorize individuals into different weight ranges that may indicate potential health risks. BMI was developed in the 19th century by Belgian mathematician Adolphe Quetelet and has since become a widely used metric in healthcare and public health.

BMI provides a simple, quick assessment that can help identify whether a person may be underweight, at a healthy weight, overweight, or obese. However, it's important to understand that BMI is just one indicator of health and doesn't measure body fat directly or account for muscle mass, bone density, overall body composition, or distribution of fat.

How is BMI Calculated?

The BMI calculation uses a simple mathematical formula:

  • Metric units: BMI = weight (kg) ÷ height (m)²
  • Imperial units: BMI = (weight (lb) × 703) ÷ height (in)²

For example, if you weigh 70 kg and are 1.75 meters tall, your BMI would be 70 ÷ (1.75 × 1.75) = 22.9, which falls in the normal weight category.

Understanding Your BMI Results

According to the World Health Organization (WHO), BMI categories for adults are:

  • Underweight (BMI below 18.5): May indicate malnutrition, eating disorders, or other health problems. Being underweight can lead to weakened immune function, osteoporosis, and fertility issues.
  • Normal weight (BMI 18.5-24.9): Generally associated with the lowest health risk. This range is considered optimal for most adults.
  • Overweight (BMI 25.0-29.9): May increase risk of cardiovascular disease, type 2 diabetes, and certain cancers. Lifestyle modifications are often recommended.
  • Obese (BMI 30.0 and above): Significantly increases risk of serious health conditions including heart disease, stroke, type 2 diabetes, and certain types of cancer.

Limitations of BMI

While BMI is a useful screening tool, it has several important limitations:

  • Doesn't distinguish between muscle and fat: Athletes and bodybuilders with high muscle mass may have a high BMI despite having low body fat.
  • Doesn't account for fat distribution: Abdominal fat (visceral fat) is more harmful than fat stored in other areas, but BMI doesn't measure this.
  • Age and gender differences: Older adults naturally have more body fat than younger adults at the same BMI. Women typically have more body fat than men at the same BMI.
  • Ethnicity variations: Different ethnic groups may have different health risks at the same BMI level.
  • Not suitable for: Children, pregnant women, elderly individuals, and people with certain medical conditions.

When to See a Doctor

You should consult with a healthcare professional if:

  • Your BMI is outside the normal range (below 18.5 or above 25.0)
  • You're experiencing unexplained weight changes
  • You have concerns about your weight or health
  • You're considering a weight loss or weight gain program
  • You have other health conditions that may be affected by your weight

A healthcare provider can perform additional assessments such as waist circumference, body fat percentage, blood tests, and evaluate your overall health to provide personalized recommendations.

Frequently Asked Questions

What is a healthy BMI range for adults?

For most adults, a BMI between 18.5 and 24.9 is considered normal or healthy. This range is associated with the lowest risk of weight-related health problems according to the World Health Organization.

Is BMI accurate for athletes and muscular people?

BMI does not distinguish between muscle and fat mass. Athletes, bodybuilders, and highly muscular individuals may have a high BMI despite having low body fat. In these cases, other measurements like body fat percentage or waist circumference may be more appropriate.

How can I lower my BMI safely?

To lower your BMI safely, focus on sustainable lifestyle changes including a balanced diet with appropriate calorie intake, regular physical activity (at least 150 minutes of moderate exercise per week), adequate sleep, and stress management. Always consult with a healthcare provider before starting any weight loss program.

How often should I check my BMI?

For most people, checking BMI every few months is sufficient. Check more frequently if you're actively trying to lose or gain weight, or as recommended by your healthcare provider during routine health reviews.

Can I use BMI during pregnancy?

BMI is not an accurate measure during pregnancy due to natural weight gain. Pre-pregnancy BMI may be used to determine healthy weight gain ranges during pregnancy, but consult your healthcare provider for personalized guidance.

Does BMI differ by age?

The standard BMI categories are designed for adults aged 20 and older. For children and teenagers, BMI is interpreted differently using age and sex-specific percentile charts. Older adults may also have different healthy BMI ranges.

What's the difference between BMI and body fat percentage?

BMI is a calculation based on height and weight, while body fat percentage measures the actual proportion of fat in your body. Body fat percentage is more accurate but requires special equipment to measure, whereas BMI can be calculated easily with just height and weight.

Is this BMI calculator accurate?

Yes, our calculator uses the standard WHO formula for BMI calculation. The accuracy of your result depends on entering your correct height and weight measurements. All calculations are performed in your browser for privacy.

Tips for Maintaining a Healthy Weight

Achieving and maintaining a healthy BMI involves more than just diet and exercise. Here are evidence-based strategies to help you maintain a healthy weight:

Nutrition

  • Eat a balanced diet rich in fruits, vegetables, whole grains, and lean proteins
  • Practice portion control and mindful eating
  • Limit processed foods, added sugars, and saturated fats
  • Stay hydrated by drinking plenty of water throughout the day
  • Plan meals ahead to avoid impulsive food choices

Physical Activity

  • Aim for at least 150 minutes of moderate aerobic activity per week
  • Include strength training exercises at least twice per week
  • Find activities you enjoy to make exercise sustainable
  • Incorporate more movement into your daily routine (take stairs, walk during breaks)
  • Start slowly and gradually increase intensity and duration

Lifestyle Factors

  • Get 7-9 hours of quality sleep each night
  • Manage stress through meditation, yoga, or other relaxation techniques
  • Avoid smoking and limit alcohol consumption
  • Track your progress but don't obsess over daily fluctuations
  • Seek support from friends, family, or support groups