BMI Calculator
Calculate your Body Mass Index (BMI) using your height and weight. Get your BMI category, estimated healthy weight range, and a clear explanation of what your result means.
Calculate Your BMI
Your BMI Result
Your BMI result will appear here.
Adult BMI Quick Reference
What Is BMI?
Body Mass Index, commonly abbreviated as BMI, is a numerical measurement based on a person’s weight and height. It is widely used as a screening tool to place adults into broad weight categories.
BMI does not directly measure body fat. Instead, it provides a simple ratio between body weight and height that can be useful when looking at weight-related health risks at a population and individual screening level.
The FreeCalz BMI Calculator accepts both metric and US customary measurements, so you can calculate BMI using kilograms and centimetres or pounds, feet and inches.
Why Is BMI Used?
BMI is easy to calculate, inexpensive to use, and does not require specialised equipment. Healthcare professionals may consider BMI alongside other measurements and health information when assessing a person’s overall health.
A BMI result should therefore be treated as one piece of information rather than a complete assessment of body composition or health.
How to Use the FreeCalz BMI Calculator
- Choose your units: Select Metric for centimetres and kilograms, or US Units for feet, inches and pounds.
- Enter accurate measurements: Use your current height and body weight for the most useful result.
- Calculate: Select Calculate BMI to see your BMI value, adult category and BMI-based weight range.
- Interpret carefully: Use BMI as a screening measure and consider other health information rather than treating the number as a diagnosis.
For a More Consistent Result
Measure height without shoes where practical and use a reliable scale for weight. If you are tracking changes over time, measuring under similar conditions can make the results easier to compare.
BMI Formula
For adults using metric measurements, BMI is calculated by dividing body weight in kilograms by height in metres squared.
For example, if a person weighs 70 kg and is 1.75 metres tall:
BMI ≈ 22.9
For US customary measurements, the equivalent calculation uses weight in pounds and height in inches:
BMI Categories for Adults
For adults, commonly used BMI categories are divided into four main ranges.
| BMI Range | Category | General Interpretation |
|---|---|---|
| Below 18.5 | Underweight | Below the commonly used healthy BMI range |
| 18.5 – 24.9 | Normal weight | Within the commonly used healthy BMI range |
| 25.0 – 29.9 | Overweight | Above the commonly used healthy BMI range |
| 30.0 or higher | Obesity | Higher BMI category requiring broader health assessment |
These categories are intended for adults and are not the same as the BMI interpretation used for children and teenagers.
What Is a Healthy Weight Range?
A commonly used adult BMI range is 18.5 to 24.9. Once your height is known, the BMI range can be converted into an approximate weight range.
The calculation is:
Maximum healthy weight = 24.9 × Height²
For example, for a height of 1.75 m:
Maximum weight: 24.9 × 1.75² ≈ 76.3 kg
This gives an approximate BMI-based range of about 56.7 kg to 76.3 kg for that height. It should not be interpreted as an individual medical target because BMI does not account for body composition or other personal factors.
Limitations of BMI
BMI is useful because it is simple, but it has important limitations.
- BMI does not directly measure body fat percentage.
- It does not distinguish between muscle mass and fat mass.
- A muscular person may have a relatively high BMI despite having a lower body-fat percentage.
- BMI does not show where body fat is distributed.
- It does not consider individual medical history or lifestyle.
- The standard adult BMI categories are not designed for children and teenagers.
For these reasons, BMI is best viewed as a screening measure rather than a diagnosis.
Factors to Consider Alongside BMI
A more complete understanding of health and weight can involve several factors in addition to BMI.
Body Composition
Muscle and bone are denser than body fat. As a result, people with substantial muscle mass can have a higher BMI without having excessive body fat.
Waist Circumference
Where body fat is stored can also be relevant to health. Measurements such as waist circumference may provide additional information about abdominal fat.
Physical Activity
Regular physical activity is an important component of overall health regardless of BMI.
Diet and Lifestyle
Eating patterns, sleep, activity levels, alcohol consumption, smoking, stress and other lifestyle factors can all contribute to health and should not be reduced to a single BMI number.
Who Should Not Use Standard Adult BMI Categories?
The standard BMI categories on this page are intended for adults. BMI is interpreted differently for children and teenagers because age and sex are considered when using growth-based reference charts.
BMI may also require additional context for athletes, people with unusually high muscle mass, older adults, pregnant women, and people with certain medical conditions.
If you are unsure how to interpret your BMI, a qualified healthcare professional can help assess it together with other relevant measurements.
Frequently Asked Questions About BMI
How Your BMI Result Is Calculated
The calculator first converts your height and weight into compatible units. It then divides your weight by the square of your height in metres. The resulting number is your BMI, which is compared with the standard adult BMI ranges shown above.
- Measure height: Use your current height without shoes where practical.
- Measure weight: Use your current body weight in kilograms or pounds.
- Convert units: US-unit inputs are converted internally before the BMI calculation.
- Apply the formula: Weight is divided by height squared.
- Interpret the result: The calculator places the result in a broad adult BMI category.
Example: 70 kg at 1.75 m
For a person weighing 70 kg and measuring 1.75 m, the calculation is 70 ÷ (1.75 × 1.75), giving a BMI of approximately 22.9. That value falls within the commonly used 18.5–24.9 adult reference range.
BMI and Weight Change
BMI can change when body weight changes, but the number alone does not tell you whether a change came from body fat, muscle, water, or another factor. For that reason, a single BMI result is less informative than looking at changes over time together with other relevant measurements.
If you are tracking weight, try to measure under reasonably consistent conditions and focus on longer-term trends rather than reacting to one day’s reading. Waist measurements, physical activity, diet, strength, and other health indicators may provide additional context.
BMI for Different Populations
The standard categories used by this calculator are intended for adults. They should not be applied to children or teenagers in the same way, because pediatric BMI is interpreted using age- and sex-specific growth references.
BMI may also need additional context for athletes and people with high muscle mass, older adults, pregnant people, and individuals with certain health conditions. A BMI value is therefore not a standalone diagnosis or a complete measure of body composition.
Related Health Calculators
What the BMI Calculator Can and Cannot Tell You
This calculator provides a mathematical BMI result from height and weight and places adults into commonly used BMI categories. It also estimates the weight range corresponding to a BMI of 18.5 to 24.9 at the entered height.
It does not measure body fat, muscle mass, waist-to-height ratio, blood pressure, blood glucose, fitness, or other health markers. A BMI result therefore works best as one screening measure within a broader assessment.
FreeCalz BMI Calculator Methodology
FreeCalz calculates adult BMI using the standard height-and-weight BMI formula. Metric inputs use kilograms and centimetres; US-unit inputs use pounds, feet and inches and are converted to metric units for the same underlying calculation.
The healthy-weight estimate shown by the calculator is derived from the 18.5 to 24.9 adult BMI reference interval at the entered height. It is an approximate mathematical range, not a personalised treatment target.
This calculator is designed for general education and screening information. It does not estimate body-fat percentage, diagnose disease, or replace an assessment by a qualified healthcare professional.