BMI Calculator
Enter your height and weight to find your BMI (Body Mass Index) and see which weight category you fall into.
What Is Body Mass Index? (BMI)
Body Mass Index (BMI) is the most widely used measurement for classifying weight categories worldwide. It is obtained by dividing your weight by the square of your height. Recognized by the World Health Organization (WHO) and health authorities everywhere, BMI serves as a fundamental indicator of whether your weight is within a healthy range. The formula is remarkably simple: BMI = weight (kg) ÷ height² (m²).
For example, a person weighing 75 kg at 1.75 m tall has a BMI of: 75 ÷ (1.75 × 1.75) = 75 ÷ 3.0625 ≈ 24.5, which falls within the normal range. Our free Body Mass Index Calculator performs this instantly — you only need to enter your height and weight to calculate BMI and see your category.
What Is a Healthy BMI? — WHO BMI Chart
The answer to what a healthy BMI is depends on the categories defined by the WHO for adults (ages 18–65). The BMI chart below shows each range, its weight category and the related health status:
| BMI Range | Category | Health Status |
|---|---|---|
| Below 16.0 | Severe Underweight | Risk of serious malnutrition |
| 16.0 – 18.5 | Underweight | Below normal; weight monitoring advised |
| 18.5 – 24.9 | Normal (Healthy) | Ideal range |
| 25.0 – 29.9 | Overweight | Increased risk of diabetes and heart disease |
| 30.0 – 34.9 | Obese Class I | Significant health risk; see a doctor |
| 35.0 – 39.9 | Obese Class II | Serious metabolic disease risk |
| 40.0 and above | Morbid Obesity (Class III) | Very high risk; medical evaluation essential |
BMI and Your Ideal Weight Range
Our calculator does more than give you a BMI value; it also computes the ideal weight range specific to your height. The lower bound of the normal range corresponds to a BMI of 18.5 and the upper bound to 24.9. For someone 170 cm tall, this range is roughly 53.5 – 72.0 kg. If your current weight is outside this range, the tool also shows how many kilograms you need to gain or lose.
BMI by Age
When interpreting BMI by age, standard thresholds do not apply to every age group:
- Children and adolescents under 18: Age- and sex-specific percentile charts are used. The standard BMI thresholds (18.5 / 25 / 30) cannot be applied directly. Percentile tracking is more reliable for child growth.
- Adults aged 18–64: The standard WHO classification applies.
- Aged 65 and over: Research suggests a range of 22–27 is more protective; being slightly overweight can be protective in this group.
- Pregnancy: BMI interpretation differs during pregnancy; only pre-pregnancy weight should be used, and separate weight-gain guidelines should be followed throughout.
Limitations of BMI — Athletes and Muscle Mass
BMI does not measure body fat distribution or the muscle-to-fat ratio. Athletes with high muscle mass may exceed the "Overweight" threshold, but this does not indicate a health risk. Likewise, older adults with reduced muscle mass may have a "Normal" BMI that hides a high body fat percentage. For this reason, BMI is far more meaningful when evaluated together with waist circumference and body fat percentage.
BMI in Daily Health Management
In daily practice, tracking BMI is one of the foundational steps of healthy weight management. Knowing your current BMI before setting weight-loss or weight-gain goals helps you use other health tools — such as calorie and basal metabolic rate calculators — more accurately. Consistently monitoring your BMI month to month lets you observe your changes over time and share them with a dietitian or doctor when needed.
How Is BMI Calculated? Step by Step
To understand how BMI is calculated, follow these steps:
- Enter your height in meters: 175 cm → 1.75 m
- Enter your weight in kilograms: for example 70 kg
- Apply the formula: BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9
- Categorize it: 22.9 → falls in the "Normal (Healthy)" range
The calculator completes these steps for you automatically; you only need to enter your height and weight.
BMI and Health: What to Watch For
A BMI value alone is not enough. When assessing your BMI from a health perspective, also consider these factors:
- Waist circumference: Abdominal fat can be a cardiovascular risk factor even when BMI is normal. A waist over 88 cm in women and 102 cm in men is considered high risk.
- Body fat percentage: BMI can be misleading for muscular individuals. A body fat measurement provides a more comprehensive assessment.
- Basal metabolic rate: Your BMR directly affects your daily calorie needs and weight-management goals. Using a BMR calculator together with BMI helps you build a more effective plan.
- Genetic and ethnic factors: For some populations of Asian descent, a BMI above 23 may be considered the overweight threshold. Follow the recommendations of your regional health authorities.
Common Uses of BMI Calculation
| Use Case | How It Helps |
|---|---|
| Weight management | Set an ideal weight target based on your goal BMI range |
| Sport and fitness | Establish a starting point before a training plan |
| Health monitoring | Track your BMI at regular intervals to see the trend |
| Child development | Monitor growth in children (alongside a percentile chart) |
You can find more information and scenarios about BMI in the frequently asked questions section below. BMI calculation is one of the cornerstones of healthy living and a preliminary assessment method frequently used during doctor visits. This free BMI calculator online needs no sign-up and runs entirely in your browser: enter your height, weight and sex to find your BMI and take a concrete step toward your target weight range. Keep up the habit of checking your BMI monthly to track your changes over time and share them with your dietitian or doctor when needed.
Frequently Asked Questions About the BMI Calculator
According to the WHO, a healthy BMI for adults is between 18.5 and 24.9. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese. For people over 65, a range of 22–27 is considered more suitable.
The BMI formula is: weight (kg) ÷ height² (m²). Example: for 70 kg and 1.75 m, BMI = 70 ÷ 3.0625 ≈ 22.9 (Normal range). You only need to enter your height and weight; the calculator applies the formula for you.
For ages 18–65 the standard WHO thresholds apply (Normal: 18.5–24.9). Over 65, a range of 22–27 is more protective. For children under 18, age- and sex-specific percentile charts are required; standard BMI thresholds do not apply to children.
No. Under the age of 18, age- and sex-specific percentile thresholds are used (BMI-for-age percentiles). The standard adult BMI classification can be misleading for children, so a percentile-based assessment should be used instead.
BMI cannot distinguish muscle from fat. Athletes with high muscle mass may reach the "Overweight" range without any real health risk. For athletes, waist circumference and body fat percentage are more reliable indicators.
Yes, the calculation (weight ÷ height²) is identical everywhere. However, some health authorities use slightly different category thresholds for certain populations (for example a lower overweight cut-off for some Asian populations).
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