Why Chemotherapy Doses Depend on Body Size: BSA Explained with Real Formulas

Chemotherapy drugs are potent medications that target rapidly dividing cells — but they also affect healthy tissue. To maximize effectiveness while minimizing toxicity, oncologists calculate chemotherapy doses based on the patient’s Body Surface Area (BSA), not simply their weight. BSA is a measurement of the total surface area of the skin, and it correlates more closely with metabolic rate, organ function, and drug clearance than body weight alone.

Calculate your own BSA with our Body Surface Area Calculator.

Average BSA by Height and Weight

Height	Weight	Average BSA (Mosteller formula)
5’0″ (152 cm)	50 kg (110 lbs)	1.45 m²
5’5″ (165 cm)	60 kg (132 lbs)	1.65 m²
5’9″ (175 cm)	70 kg (154 lbs)	1.84 m²
5’10” (178 cm)	75 kg (165 lbs)	1.92 m²
6’0″ (183 cm)	80 kg (176 lbs)	2.01 m²
6’2″ (188 cm)	90 kg (198 lbs)	2.16 m²

The average adult BSA is approximately 1.7 m² (standard reference used for many drug dosages). Most chemotherapy doses are calculated as mg per m² of BSA. For example, a common drug like carboplatin is dosed at AUC 5-6 (area under the curve) per the Calvert formula, which uses BSA and renal function.

BSA Formulas: How They Compare

Formula	Year	Equation	Best For
Mosteller	1987	√(height(cm) × weight(kg) / 3600)	General use, simplest
Du Bois & Du Bois	1916	0.007184 × height(cm)^0.725 × weight(kg)^0.425	Adults, most widely cited
Haycock	1978	0.024265 × height(cm)^0.3964 × weight(kg)^0.5378	Children and infants
Gehan & George	1970	0.0235 × height(cm)^0.42246 × weight(kg)^0.51456	Obese patients
Boyd	1935	0.0003207 × height(cm)^0.3 × weight(g)^(0.7285 – 0.0188 × log(weight(g)))	Very wide weight range

The Mosteller formula is the most commonly used in clinical practice today because it is simple and accurate enough for most patients. The Du Bois formula remains the most cited in medical literature and is the standard used in many oncology protocols.

Why BSA Instead of Just Weight?

Drug metabolism and clearance rates correlate more strongly with BSA than with body weight. This is because BSA reflects the size of metabolically active organs (liver, kidneys) more accurately than weight alone. Two patients of the same weight can have very different BSA values — for example, a tall, thin person (180 cm, 70 kg) has a BSA of 1.88 m², while a short, stocky person (160 cm, 70 kg) has a BSA of 1.73 m². The same chemotherapy dose in mg/m² would give the first patient about 9% more drug.

When Weight-Based Dosing Is Used Instead

Not all cancer drugs use BSA-based dosing. Some newer targeted therapies and immunotherapies (like pembrolizumab/Keytruda) use fixed doses regardless of BSA. Drugs with narrow therapeutic windows may use either BSA or adjusted body weight. For obese patients (BMI > 30), many oncologists use actual body weight for BSA calculation rather than ideal body weight, based on evidence from the American Society of Clinical Oncology (ASCO) guidelines.

Frequently Asked Questions

What is a normal BSA? The average adult BSA is 1.7 m². Men typically range from 1.8 to 2.0 m²; women range from 1.6 to 1.8 m². Newborns have a BSA of about 0.2 m².

Does BSA change with age? Yes. BSA increases rapidly during childhood, peaks in young adulthood, and gradually declines by about 5-10% in older age due to changes in body composition and height loss.

Can I calculate my own BSA at home? Yes. BSA requires only your height and weight. Use our Body Surface Area Calculator for an instant result using the Mosteller formula.

Is BSA the same as BMI? No. BMI (Body Mass Index) measures weight relative to height squared and is used for obesity classification. BSA measures the total surface area of the body and is used for metabolic and dosing calculations. A person with a high BMI can have a normal BSA, and vice versa.

Use our Body Surface Area Calculator to compute your BSA using multiple formulas, and compare results with the standard reference values.