BSA Calculator

Introduction

Body Surface Area (BSA) is a measurement of the total area of skin that covers your body. Doctors and nurses use BSA to figure out the right dose of medicine, especially for treatments like chemotherapy. It is also helpful for checking kidney function and heart health. Unlike body weight alone, BSA gives a more accurate picture of your body size because it takes both your height and weight into account.

This BSA Calculator makes it quick and easy to find your body surface area. Simply enter your height and weight, and the tool does the math for you. It uses trusted formulas that doctors rely on every day. Whether you are a healthcare worker, a student, or just someone who wants to learn more about their body metrics, this calculator gives you a fast and reliable result.

How to Use Our BSA Calculator

Enter your height and weight below to quickly calculate your body surface area (BSA). The calculator will give you your BSA result in square meters (m²).

Height: Type in your height using either centimeters or inches. This is how tall you are from head to toe. You can measure your height by standing straight against a wall. If you're interested in how your height relates to other body proportions, try our Waist to Height Ratio Calculator.

Weight: Type in your body weight using either kilograms or pounds. For the best result, weigh yourself in the morning before eating. You can also use our Ideal Body Weight Calculator to see how your current weight compares to recommended ranges.

Formula (if available): Some BSA calculators let you pick a formula. The most common ones are the Du Bois formula and the Mosteller formula. If you are not sure which one to use, the Mosteller formula is a good default choice because it is simple and widely accepted.

Once you enter your numbers and click calculate, the tool will show your body surface area in square meters. BSA is used by doctors to figure out the right dose of certain medicines, especially chemotherapy drugs. It is also helpful for understanding your body size in a way that accounts for both height and weight. A typical adult BSA ranges from about 1.5 to 2.0 m².

What Is Body Surface Area (BSA)?

Body Surface Area, or BSA, is a measure of the total outer area of your body, expressed in square meters (m²). Doctors and nurses use BSA to make important medical decisions, such as figuring out the right dose of certain drugs (especially chemotherapy), estimating kidney function, measuring cardiac output, and assessing burn injuries. Unlike body weight alone, BSA gives a more accurate picture of your body's size because it accounts for both your height and weight together.

How Is BSA Calculated?

There is no single way to measure BSA directly without complex 3D scanning, so scientists have developed mathematical formulas to estimate it. The most common formula is the Du Bois & Du Bois formula, created in 1916, which uses your weight and height in a specific equation. Other well-known formulas include Mosteller (a simpler version popular in clinics), Haycock (often used for infants and children), and Gehan & George (common in cancer treatment dosing). Each formula uses slightly different math, but they all produce very similar results for most people.

Why Are There So Many BSA Formulas?

Different formulas were developed over the years to better fit certain groups of people. For example, the Fujimoto and Takahira formulas were designed using data from Japanese and East Asian populations. The Schlich formula accounts for differences between males and females. The Boyd formula is a classic equation that uses a more complex calculation. While the differences between formulas are usually small — often less than 5% — those small differences can matter when dosing powerful medications. Your doctor will choose the formula that best fits your situation.

What Is a Normal BSA?

The average adult BSA falls between 1.7 and 2.0 m². Men tend to have a higher BSA (around 1.9 m²) than women (around 1.6 m²) because they are generally taller and heavier. A newborn baby has a BSA of about 0.25 m², and a six-year-old child is around 0.8 m². Your BSA naturally changes as you grow, gain weight, or lose weight. To understand your body composition in more detail, you might also explore our Lean Body Weight Calculator.

BSA vs. BMI: What's the Difference?

BSA measures your body's total surface area and is mainly used in clinical and medical settings. BMI (Body Mass Index) is a ratio of your weight to your height squared, and it is used to classify whether a person is underweight, normal weight, overweight, or obese. This calculator provides both values so you can see a complete picture of your body metrics. A healthy BMI range for most adults is 18.5 to 24.9 kg/m². For additional body proportion insights, check out our Waist to Hip Ratio Calculator.

Why Does BSA Matter in Medicine?

• Drug dosing: Many chemotherapy drugs and some antibiotics are dosed based on BSA rather than body weight to reduce the risk of giving too much or too little medication.
• Kidney function: Glomerular filtration rate (GFR), which measures how well your kidneys filter blood, is often adjusted to BSA.
• Cardiac index: Heart performance can be measured per unit of BSA, giving doctors a standardized way to compare heart function across patients of different sizes. You can learn more about heart health with our Heart Rate Zone Calculator.
• Burn assessment: The percentage of BSA affected by burns helps medical teams decide on fluid replacement and treatment plans.

Understanding your BSA is just one part of a complete health picture. Consider pairing this tool with our Macro Calculator for nutritional planning, our Water Intake Calculator for hydration goals, or our VO2 Max Calculator to assess your cardiovascular fitness. Athletes may also find the FFMI Calculator useful for evaluating fat-free mass relative to body size.

Important: This BSA calculator is meant for educational purposes only. It should not replace advice from a doctor, pharmacist, or other qualified healthcare professional. Always consult your medical provider before making any health or treatment decisions based on these results.

Frequently Asked Questions

What is a BSA calculator used for?

A BSA calculator estimates the total surface area of your body in square meters (m²). It uses your height and weight to give a result. Doctors use BSA to dose medicines like chemotherapy, check kidney function, measure heart performance, and plan burn treatment.

Which BSA formula is the most accurate?

No single formula is the most accurate for everyone. The Du Bois & Du Bois formula is the most widely used standard. Haycock works best for children and babies. Schlich is better when gender differences matter. Your doctor will pick the best formula for your specific case.

Can I use this BSA calculator for a child or baby?

Yes, but you should pay attention to the formula used. The Haycock formula was designed and validated for infants and children. The calculator includes this formula and shows its result alongside others. For very small babies, results may be less precise, so always confirm with a pediatrician.

What units do I need to enter my height and weight in?

You can enter weight in kilograms (kg), pounds (lbs), or grams (g). For height, you can use feet and inches or centimeters (cm). The calculator converts between units automatically, so use whichever you are comfortable with.

Why does this calculator show different BSA values for different formulas?

Each formula uses slightly different math and was built using data from different groups of people. This means the results vary a little. For most adults, the difference is small — usually less than 5%. The calculator shows all formulas so you can compare them side by side.

What does the Target BMI field do?

The Target BMI field is optional. If you type in a BMI goal (like 22), the calculator shows how much you would need to weigh to reach that BMI at your current height. It also shows what your BSA would be at that target weight.

Why does gender matter for BSA calculation?

Most BSA formulas do not use gender. However, the Schlich formula does. It has separate equations for males and females because body proportions differ between the two. Selecting your gender ensures the Schlich result is correct.

How is BSA different from body weight?

Body weight is just how heavy you are. BSA measures the total outer area of your body. Two people can weigh the same but have different BSAs if one is taller. BSA is more useful in medicine because it better reflects how the body processes drugs and loses heat.

What does BSA have to do with chemotherapy dosing?

Many chemotherapy drugs are dosed in milligrams per square meter (mg/m²) of BSA. This method helps doctors give a dose that matches each patient's body size, which lowers the risk of giving too much or too little of a powerful drug.

Is a higher BSA always bad?

No. BSA is not a health score. It simply describes your body's surface area. Taller and heavier people naturally have a higher BSA. It is a neutral measurement used for medical calculations, not a sign of good or bad health on its own.

What does BMI Prime mean in the results?

BMI Prime is your BMI divided by 25. A value of 1.0 means your BMI is exactly 25, which is the upper limit of the normal range. A value below 1.0 means you are within or below normal weight. A value above 1.0 means you are above normal weight.

Can I trust this calculator for medical decisions?

This calculator uses the same formulas that doctors use, but it is meant for educational purposes only. You should never change medications or treatments based on these results alone. Always talk to your doctor or pharmacist before making health decisions.

What is the ideal weight range shown in the BMI section?

The ideal weight range shows the weights that would give you a BMI between 18.5 and 24.9 kg/m² at your current height. This is the range that most health organizations consider normal for adults.

Why do the BSA vs. Weight chart lines curve instead of being straight?

BSA formulas use exponents (powers) of weight and height, not simple multiplication. This means as weight goes up, BSA increases at a slowing rate. That is why the lines on the chart curve upward but gradually flatten out at higher weights.

What happens if I enter a very unusual weight or height?

The calculator will show a warning if your values fall outside the typical range. Results may still appear, but they could be less accurate because the formulas were developed using data from people within common height and weight ranges. Extreme values are flagged with an orange warning message.