BMI Calculator: Formula, Normal Range, Categories & Healthy Weight
Learn how Body Mass Index (BMI) is calculated using height and weight. Understand the BMI formula, adult BMI categories, healthy weight range, clinical significance, interpretation, and important limitations.
BMI Calculator
Calculate BMI using your height and weight and quickly determine the corresponding adult BMI category.
Open BMI Calculator →What Is BMI?
Body Mass Index (BMI) is a commonly used weight-for-height index for assessing weight status in adults. It is calculated from a person's body weight and height and is expressed in kg/m².
BMI is useful as a population-level and individual screening measure for underweight, overweight, and obesity. However, it does not directly measure body fat or distinguish between fat mass and lean muscle mass.
The World Health Organization defines BMI as body weight in kilograms divided by height in metres squared. 1
BMI is an anthropometric screening measure, not a complete assessment of an individual's health. A BMI result should be interpreted together with factors such as waist circumference, body composition, medical history, metabolic risk factors, and overall clinical context.
Use the LabProSuite BMI Calculator to calculate BMI from height and weight.
BMI Formula
The standard adult BMI formula uses body weight in kilograms and height in metres.
For example, if an adult weighs 70 kg and has a height of 1.75 m:
BMI = 22.9 kg/m²
This example falls within the standard adult normal-weight BMI range. WHO provides the same calculation method for adult BMI. 2
How to Convert Height for BMI Calculation
BMI requires height in metres when weight is entered in kilograms. If height is provided in centimetres, divide the height by 100.
For example, a height of 160 cm is equal to 1.60 m.
Adult BMI Categories
For adults, commonly used international BMI categories classify underweight, normal weight, overweight, and obesity. WHO describes BMI below 18.5 as underweight, 18.5–24.9 as normal weight, 25.0–29.9 as pre-obesity/overweight, and 30 or above as obesity. 3
| BMI (kg/m²) | Adult Classification |
|---|---|
| <18.5 | Underweight |
| 18.5–24.9 | Normal weight |
| 25.0–29.9 | Overweight / Pre-obesity |
| 30.0–34.9 | Obesity Class I |
| 35.0–39.9 | Obesity Class II |
| ≥40.0 | Obesity Class III |
What Is a Normal BMI?
For adults, a BMI from 18.5 to 24.9 kg/m² is commonly classified as the normal-weight range. 4
However, a BMI within this range does not automatically mean that a person has ideal body composition or low cardiovascular risk. BMI should be considered alongside other health indicators.
How to Calculate a Healthy Weight Range From BMI
For a given adult height, an approximate weight range corresponding to a BMI of 18.5–24.9 can be calculated using the inverse BMI formula.
Therefore, for a specific height:
- Lower reference weight ≈ 18.5 × height²
- Upper reference weight ≈ 24.9 × height²
Example: For an adult with a height of 1.70 m:
Lower reference weight: 18.5 × 1.70² ≈ 53.5 kg
Upper reference weight: 24.9 × 1.70² ≈ 72.0 kg
This represents the approximate weight range corresponding to the standard BMI range of 18.5–24.9.
BMI Calculation Example
Consider an adult with:
- Weight: 80 kg
- Height: 1.70 m
BMI is calculated as:
BMI ≈ 27.7 kg/m²
A BMI of approximately 27.7 kg/m² falls within the adult overweight range under the standard classification.
Calculate Your BMI
Enter your height and weight in the LabProSuite BMI Calculator for an instant BMI result and category.
Calculate BMI →Why Is BMI Clinically Important?
Higher BMI is associated with increased risk of several chronic conditions, including cardiovascular disease, type 2 diabetes, high blood pressure, and certain cancers. WHO notes that increasing BMI is associated with increasing risk for several noncommunicable diseases. 5
BMI can therefore be useful as one component of an overall health and risk assessment, particularly when followed over time.
Limitations of BMI
BMI has several important limitations because it is calculated only from height and weight.
- BMI does not directly measure body fat percentage.
- BMI does not distinguish muscle mass from fat mass.
- A muscular individual may have a high BMI without having excessive body fat.
- BMI does not show where body fat is distributed.
- Waist circumference may provide additional information about central adiposity.
- Age, sex, ethnicity, body composition, and clinical conditions can affect interpretation.
BMI should be considered a screening tool rather than a standalone diagnostic test. When BMI appears inconsistent with the clinical picture, additional anthropometric or clinical assessment may be appropriate.
BMI and Waist Circumference
BMI provides information about weight relative to height, but it does not describe the distribution of body fat.
Waist circumference can provide additional information about central adiposity and metabolic risk. WHO also notes that additional measurements such as waist circumference can help in assessing obesity. 6
Is the Adult BMI Calculator Suitable for Children?
No. Adult BMI categories should not simply be applied to children and adolescents.
For children and adolescents, BMI is interpreted according to age- and sex-specific growth references or percentiles. WHO states that the thresholds used for children and adolescents differ from adult BMI cut-offs. 7
This LabProSuite article describes standard adult BMI interpretation. For children and adolescents, age- and sex-specific growth references should be used.
Can BMI Be Used During Pregnancy?
BMI is generally not used in the same way to assess weight status during pregnancy because pregnancy involves expected changes in body weight and composition.
Pregnancy weight management should therefore be assessed using appropriate prenatal guidance and clinical evaluation rather than interpreting a current pregnancy weight with standard adult BMI categories alone.
BMI vs Body Fat Percentage
| Feature | BMI | Body Fat Measurement |
|---|---|---|
| Uses height | Yes | Usually not directly |
| Uses body weight | Yes | May be used depending on method |
| Measures body fat directly | No | Some methods estimate body fat |
| Distinguishes muscle from fat | No | Some methods can provide additional information |
| Simple screening tool | Yes | Depends on method |
How to Use the LabProSuite BMI Calculator
- Enter your body weight.
- Enter your height.
- Select the appropriate units if available.
- Click the calculate button.
- Review your calculated BMI.
- Check the corresponding adult BMI category.
- Interpret the result together with other health information.
Use the LabProSuite BMI Calculator to calculate BMI quickly from height and weight.
Frequently Asked Questions About BMI
What is BMI?
BMI stands for Body Mass Index. It is calculated by dividing body weight in kilograms by height in metres squared.
What is the BMI formula?
BMI = Weight (kg) ÷ Height² (m²).
What is a normal BMI?
For adults, a BMI of 18.5–24.9 kg/m² is commonly classified as normal weight.
What BMI is considered overweight?
For adults, a BMI of 25.0–29.9 kg/m² is commonly classified as overweight or pre-obesity.
What BMI is considered obesity?
For adults, a BMI of 30 kg/m² or higher is classified as obesity.
Is BMI the same as body fat percentage?
No. BMI is calculated from height and weight and does not directly measure body fat percentage.
Can a muscular person have a high BMI?
Yes. BMI does not distinguish muscle mass from fat mass, so a muscular person may have a higher BMI without having excessive body fat.
Is BMI different for children?
Yes. Children and adolescents require age- and sex-specific BMI interpretation rather than adult BMI categories.
Can BMI be used during pregnancy?
Standard adult BMI categories are not intended to assess pregnancy weight status. Pregnancy weight should be evaluated using appropriate prenatal guidance and clinical assessment.
Is BMI enough to assess health?
No. BMI is a screening measure and should be interpreted with other clinical and anthropometric information such as waist circumference, body composition, medical history, and metabolic risk factors.
Conclusion
Body Mass Index (BMI) is a simple and widely used measure calculated from weight and height. For adults, it can help classify weight status into underweight, normal weight, overweight, and obesity categories.
However, BMI does not directly measure body fat and should not be considered a complete assessment of health. Body composition, waist circumference, medical history, metabolic risk factors, and other clinical information may provide important additional context.
For a quick calculation, use the LabProSuite BMI Calculator to calculate BMI from height and weight.
Disclaimer
This article and calculator are provided for educational and laboratory reference purposes only. BMI is a screening measure and should not be used as the sole basis for diagnosis, treatment, or medical decision-making.
Clinical interpretation should be performed by a qualified healthcare professional using the individual's complete clinical history, anthropometric measurements, laboratory findings, applicable guidelines, and other relevant information.
References
Nutrition for a healthy life — BMI and healthy body weight
Obesity and Overweight
BMI definitions and adult classification
