Body Surface Area (BSA) Calculator

Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer Last updated: August 20, 2026

Disclaimer: This calculator is provided for informational and educational purposes only and does not constitute financial, medical, legal, or other professional advice. Always consult a qualified professional before making decisions based on these results.

📚 Confused about how this is calculated? Read the full Why Life Scales by Surface, Not by Weight →

Why Body Surface Area Beats Body Weight

Weight alone is a blunt instrument for describing how much of a person there is. Two people at 70 kg can differ substantially in the amount of skin, and therefore in the amount of metabolic surface, they carry. Body surface area (BSA) captures that dimension in a single figure expressed in square metres, and it has become the reference denominator in contexts where scaling to body size matters more than scaling to mass alone — chemotherapy protocols, cardiac index, and burn assessment among them. This calculator applies the Mosteller formula, which survives because it is the rare clinical shortcut that is both defensible and computable in your head.

The Formula

This calculator uses the Mosteller equation exactly as published:

BSA (m²) = √( (Height (cm) × Weight (kg)) ÷ 3600 )

The elegance is in the constant. 3600 is simply 60 × 60, which means a person 60 cm tall weighing 60 kg would have a BSA of exactly 1.00 m². Everything else scales from that anchor as the square root of the height-weight product — which is why BSA rises much more gently than weight does.

Mosteller BSA Reference Grid

Every value below was computed with the same formula this calculator runs:

Body surface area in m² by height and weight (Mosteller)
Height	50 kg	60 kg	70 kg	80 kg	90 kg	100 kg
150 cm	1.44	1.58	1.71	1.83	1.94	2.04
160 cm	1.49	1.63	1.76	1.89	2.00	2.11
170 cm	1.54	1.68	1.82	1.94	2.06	2.17
180 cm	1.58	1.73	1.87	2.00	2.12	2.24
190 cm	1.62	1.78	1.92	2.05	2.18	2.30

Read across a row and note how doubling weight from 50 kg to 100 kg raises BSA by only about 42% — the square-root relationship at work.

The Square-Root Curve

BSA at 170 cm across a 50 kg range of body weight. The bars climb, but they flatten — surface area is far less sensitive to mass than mass is to itself.

Where BSA Is Actually Used

Oncology dosing — many cytotoxic agents are prescribed in mg/m², making BSA the direct multiplier that turns a protocol dose into a patient dose.
Cardiac index — cardiac output divided by BSA normalises pump performance across body sizes, so a 1.5 m² patient and a 2.2 m² patient can be compared on the same scale.
Renal reporting — eGFR is conventionally reported per 1.73 m², a historical "average adult" BSA, which is why that odd-looking number appears in every lab report.
Fluid and burn calculations — surface-area-based estimates underpin several established resuscitation and metabolic formulas.

Mosteller Versus the Alternatives

Mosteller is not the only BSA equation — Du Bois, Haycock, and Boyd all predate or compete with it. Mosteller earned its place in 1987 by producing results in close agreement with the older equations while reducing the arithmetic to a single square root. When a formula is going to be used at a bedside under time pressure, tractability is a feature, not a compromise.

Note: This tool is a general reference for understanding the Mosteller calculation. It is not medical advice and must not be used to determine a real medication dose. Any dosing decision belongs with a qualified clinician or pharmacist working from the actual prescribing information.

How to Use This Calculator

Enter Height (cm). If you have height in inches, multiply by 2.54 first.
Enter Weight (kg). From pounds, divide by 2.20462.
Select Calculate. The result returns BSA rounded to two decimal places, with the intermediate square-root step shown so the arithmetic can be checked by hand.

Related Calculations

BSA is the denominator behind eGFR, which reports kidney function per 1.73 m². For the mass-based alternative to surface-area dosing, see the Medication Dosage Calculator.

Principles of Pharmacokinetics and Body Surface Area (BSA)

A Body Surface Area (BSA) calculator computes the total external surface area of the human body in square meters (m²). In clinical oncology, pediatric pharmacotherapy, and cardiology, BSA provides a physiological dosing metric superior to total body weight because it correlates directly with metabolic rate, cardiac output, and renal glomerular filtration rate.

The Fundamental BSA Formulas in Clinical Medicine

Mosteller Formula (Universal Clinical Standard): BSA (m²) = √[ ( Height (cm) × Weight (kg) ) / 3,600 ]
DuBois & DuBois Formula: BSA (m²) = 0.007184 × Height (cm)^0.725 × Weight (kg)^0.425
Haycock Formula (Pediatrics): BSA (m²) = 0.024265 × Height (cm)^0.3964 × Weight (kg)^0.5378
Average Adult BSA Reference: Men ≈ 1.90 m² | Women ≈ 1.60 m²

Step-by-Step Worked Calculation Example

Example: Calculating Chemotherapy Dosage for an Oncology Patient

Problem: A cancer patient measures Height = 175 cm and Weight = 72 kg. Chemotherapy protocol mandates a Carboplatin dose of 300 mg/m² of BSA. Calculate: (1) Patient BSA using Mosteller formula; and (2) Total prescribed chemotherapy dose in milligrams.

Step 1: Calculate BSA (Mosteller):

BSA = √[ ( 175 × 72 ) / 3,600 ] = √[ 12,600 / 3,600 ] = √[ 3.50 ] = 1.87 m²

Step 2: Calculate Prescribed Chemotherapy Dose:

Total Dose = 1.87 m² × 300 mg/m² = 561.0 mg Carboplatin

Conclusion: Dosing based on 1.87 m² BSA avoids under-dosing or severe chemotherapy toxicity.

Cardiac Index (CI) Normalization via BSA

In intensive care cardiology and hemodynamic monitoring, total Cardiac Output (CO in L/min) is normalized to body surface area to compute the Cardiac Index (CI):

Cardiac Index (CI) = Cardiac Output (L/min) / Body Surface Area (m²)
Normal Physiological Range: 2.50 to 4.00 L/min/m²
Cardiogenic Shock Threshold: CI < 2.20 L/min/m² with elevated pulmonary capillary wedge pressure.

BSA Dosing in Narrow Therapeutic Index Chemotherapy

In medical oncology, antineoplastic agents (such as Doxorubicin, Cisplatin, and Paclitaxel) have a narrow therapeutic window:

Dosing based precisely on Body Surface Area prevents life-threatening bone marrow suppression and cardiotoxicity while ensuring sufficient systemic drug concentrations to achieve tumor eradication.

BSA in Pediatric Burn Resuscitation

In pediatric emergency medicine and burn trauma surgery, fluid resuscitation formulas (Parkland / Galveston formulas) calculate 24-hour lactated Ringer's IV fluid requirements based on total burned Body Surface Area (5,000 mL/m² BSA burned), preventing hypovolemic burn shock.

BSA Normalization in Renal Pharmacotherapy

While standard Cockcroft-Gault Creatinine Clearance outputs unadjusted mL/min, nephrology staging equations normalize glomerular filtration to a standard body surface area of 1.73 m², allowing standardized cross-patient comparison of chronic kidney disease progression.

Precision Pharmacotherapy Dosing

Utilizing validated Body Surface Area formulas ensures therapeutic drug concentrations are achieved safely in high-risk clinical oncology and critical care regimens.

Clinical BSA Assessment

Routine Body Surface Area calculation remains an essential bedside clinical pharmacology tool, directly guiding safe and effective individualized drug dosing for critically ill and oncology patients worldwide.

Patient Safety in Dosing

Accurate BSA measurement remains fundamental to safe individualized medication dosing across all clinical specialties.