BMI Calculator (Body Mass Index and BSA)

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BMI Calculator (Body Mass Index and BSA)

Estimates body mass index for weight classification and body surface area for medical dosing and clinical assessments

All tools /

BMI Calculator (Body Mass Index and BSA)

Estimates body mass index for weight classification and body surface area for medical dosing and clinical assessments

Weight

Enter your weight in kilograms

Height

Enter your height in centimeters

BMI — (), BSA — m²

0/2 answered · enter values to update

Instructions

The BMI and BSA calculators use height and weight to provide quick clinical estimates.

BMI (Body Mass Index):
BMI is a screening tool that classifies weight in relation to height. It helps identify underweight, healthy weight, overweight, and obesity, which are linked to various health risks.

BSA (Body Surface Area):
BSA is a measure of the body’s external surface area. It is commonly used to adjust drug dosing, calculate cardiac index, and interpret renal function.

Overview

When to use

Why use

Evidences

Interpretation

BMI (kg/m2) = Weight (kg) / Height (m2)

BSA (m2) = Squareroot[(Height (cm)×Weight (kg)) / 3600]

BMI Table:

BMI Range	Category
< 18.5	Underweight
18.5-24.9	Normal
25.0-29.9	Overweight
30.0-34.9	Obesity – Class I (Moderate risk)
35.0-39.9	Obesity – Class II (High risk)
>40.0	Obesity – Class III (Severe risk)

BSA Table:

BSA Range (m2)	Interpretation
<1.5	Small body surface
1.5-2.0	Typical adult range
>2.0	Large body surface
>2.5	Very large body surface

Mosteller introduced a simplified and accurate BSA formula, BSA(m²)=√([height(cm)×weight(kg)]/3,600), which remains widely used due to ease and performance. Comparative studies in children and adults show Mosteller’s and Boyd’s equations have the smallest bias versus reference methods, supporting clinical use across ages. The classical DuBois and DuBois BSA equation is the historical foundation for BSA estimation in clinical dosing and normalization
https://pubmed.ncbi.nlm.nih.gov/3657876/

BMI associates with cardiometabolic risk in large cohorts. A prospective study from the Physicians’ Health Study (n=13,563; median 14.5 years) found a strong gradient between higher BMI and incident hypertension, even within the normal to mildly overweight range. In patients with stable coronary disease, a U-shaped relationship was observed between BMI and cardiovascular and all-cause mortality, with lowest risk around BMI≈27, and higher risk at BMI<20 or ≥35.
https://www.ahajournals.org/doi/10.1161/JAHA.121.023667

Overview

When to use

Why use

Evidences

The BMI and BSA calculators serve different but complementary roles in clinical medicine.

BMI is a public health and screening tool that classifies weight status, helping identify risks for conditions such as diabetes, hypertension, and cardiovascular disease. Despite its limitations in athletes, elderly, and some ethnic groups, BMI remains widely adopted for population surveillance and risk stratification.
BSA is essential in clinical dosing and physiology, offering a standardized measure of body surface. It is critical for safe chemotherapy administration, pediatric dosing, GFR normalization, and cardiac output interpretation. Unlike BMI, it is not a measure of obesity but a scaling factor for body size.
Together, these tools provide a fuller picture: BMI for health risk screening and BSA for precise medical calculations.

Overview

When to use

Why use

Evidences

Interpretation

BMI (kg/m2) = Weight (kg) / Height (m2)

BSA (m2) = Squareroot[(Height (cm)×Weight (kg)) / 3600]

BMI Table:

BMI Range	Category
< 18.5	Underweight
18.5-24.9	Normal
25.0-29.9	Overweight
30.0-34.9	Obesity – Class I (Moderate risk)
35.0-39.9	Obesity – Class II (High risk)
>40.0	Obesity – Class III (Severe risk)