⚖️ BMI Calculator

Simply enter your height and weight to calculate your BMI (Body Mass Index) and obesity in real time.

Your BMI
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BMI Formula

BMI = Weight(kg) / Height(m)²2

BMI (Body Mass Index) is an international indicator of obesity calculated from the relationship between weight and height.

Example: Height 170cm, Weight 65kg

BMI = 65 / (1.70 × 1.70) = 65 / 2.89 = 22.49

BMI Criteria (Japan Society for the Study of Obesity)

BMI judgment WHO Standard
Under 18.5 低体重（やせ） Underweight
18.5 ~ 24.9 普通体重 Normal range
25.0 ~ 29.9 肥満（度1） Pre-obese
30.0 ~ 34.9 肥満（度2） Obese class I
35.0 ~ 39.9 肥満（度3） Obese class II
40.0 or above 肥満（度4） Obese class III

Usage and Application Examples

  • Simply enter your height and weight and your BMI will be calculated in real time!
  • Gauge allows you to see at a glance where your BMI stands overall
  • Appropriate and normal weight ranges are displayed and used for goal setting
  • Compare the results with the results of your physical examination to help you manage your health.

What is BMI Calculator?

BMI Calculator instantly computes Body Mass Index from height and weight measurements, providing a standard metric for assessing body composition categories. The calculator displays real-time results with immediate classification into underweight, normal, overweight, and obese categories. This free online tool helps individuals track health metrics without complex calculations, supporting both metric and imperial measurement systems.

How to Use

Enter your height using available units: meters with decimals (1.75) or feet and inches separately. Input your weight in kilograms or pounds depending on your preference. The calculator displays instant results showing your BMI number and corresponding health category. Most calculators provide color-coded categories for quick visual reference. Some tools include historical tracking to monitor BMI changes over time. Select your gender and age if the tool includes additional health metrics beyond basic BMI.

Use Cases

Fitness enthusiasts use BMI calculators to establish baseline health metrics when starting exercise programs. Healthcare providers reference BMI during initial patient consultations as a conversation starting point. Weight loss planners track BMI improvements as motivation and milestone markers. Students and educators use the tool to teach health concepts and body composition fundamentals in classroom settings. Insurance and occupational health programs use BMI data for wellness program eligibility assessment.

Tips & Insights

BMI categorization varies slightly between organizations; standard ranges are underweight (below 18.5), normal (18.5–24.9), overweight (25–29.9), and obese (30+). BMI alone doesn't distinguish between muscle and fat, so athletic individuals may register higher BMI despite healthy composition. Waist circumference and body fat percentage provide complementary assessment. Age-adjusted BMI categories exist for children and differ from adult ranges significantly.

Frequently Asked Questions

What is BMI?

BMI (Body Mass Index), also called Body Mass Index, is an index of obesity calculated from weight and height. The formula is "weight (kg) / height (m) squared. It is an international standard established by the World Health Organization (WHO) and widely used for health management.

What is a healthy range of BMI?

According to the standards of the Japan Society for the Study of Obesity, a BMI of 18.5 to 24.9 is considered "normal weight." A BMI of 22 is considered the standard value that is least likely to cause illness, and the appropriate weight is calculated based on this value.

What is the formula for calculating BMI?

BMI = Weight (kg) / (Height (m) x Height (m)). For example, for a height of 170 cm and weight of 65 kg, BMI = 65 / (1.70 x 1.70) = 22.49.

What are the limitations of BMI?

Since BMI does not directly measure body fat percentage, athletes with high muscle mass may have a higher BMI. In addition, since it does not take into account age, gender, or body composition, BMI alone cannot be used to determine health status. It should be used as a guide only.

How do you calculate the correct weight?

Proper weight is calculated as "Height (m) x Height (m) x 22", where BMI 22 is the value that is statistically considered to be the least likely to cause illness. For example, for a height of 170 cm, the appropriate weight is 1.70 x 1.70 x 22 = 63.6 kg.

Is the same formula used for BMI for children?

The formula is the same, but the judgment criteria are different. Since children are evaluated based on percentile values for each age and gender, the judgment criteria of this calculator (for adults) are for those 18 years of age and older.

Can I use different units (pounds and inches) instead of kg and cm?

Yes, this calculator supports both metric (kg/cm) and imperial (lbs/inches) units. You can switch between units using the dropdown menu at the top of the calculator. The BMI calculation automatically adjusts the formula based on your selected units, ensuring accurate results every time.

How do I interpret my BMI results?

BMI results are typically categorized as: Underweight (under 18.5), Normal weight (18.5-24.9), Overweight (25-29.9), and Obese (30+). The calculator displays your result with a color-coded indicator and corresponding health category. Most healthcare professionals recommend aiming for a BMI in the normal weight range, though individual health varies based on other factors.

How often should I recalculate my BMI?

It's recommended to calculate your BMI monthly or quarterly to track long-term trends rather than daily fluctuations. If you're on a weight management program, tracking every 2-4 weeks provides meaningful data to assess progress. This frequency allows you to see patterns without being discouraged by short-term weight variations.

Does BMI account for muscle mass?

No, BMI does not distinguish between muscle and fat, so athletes with significant muscle mass may have a higher BMI despite being healthy. For accuracy in these cases, body composition analysis or measurements like body fat percentage are more appropriate. If you have significant muscle mass, consult your healthcare provider for a comprehensive health assessment.

Is there a different BMI formula for different age groups?

While the BMI formula is the same across age groups, interpretation differs significantly. Adult categories (18+) use standard ranges, but children and teens have age- and sex-specific percentile-based categories. This calculator uses adult BMI standards; for children, consult pediatric BMI charts or your healthcare provider.

Can I use BMI to determine if I need to lose or gain weight?

BMI is one useful tool for general health assessment, but weight changes should always be discussed with a healthcare provider considering your complete health picture. While BMI can suggest whether weight adjustment might be beneficial, factors like fitness level, family history, and medical conditions also matter significantly. Your doctor can provide personalized guidance based on your individual circumstances.