Body Surface Area (BSA) Calculations for Nurses
Body surface area is the gold standard for dosing chemotherapy drugs and certain pediatric medications because it more accurately reflects how the body distributes and eliminates drugs than weight alone. A nurse who understands BSA can verify chemotherapy orders, recognize dosing inconsistencies, and educate patients about why their dose is individualized. This page covers the two main BSA formulas, reference values for common body types, and how to apply BSA to a drug dose.
Clinical Disclaimer: This reference is for educational purposes. Always verify drug doses with a pharmacist and follow your institution's protocols. BSA-based chemotherapy orders must be independently verified by two licensed clinicians before administration.
How to Calculate BSA
Two formulas are in common clinical use. The Mosteller formula is preferred in most institutions for its simplicity and accuracy. The DuBois formula (1916) is older and more complex but gives virtually identical results in the normal adult range. Both require height in centimeters and weight in kilograms — convert from inches and pounds if needed before applying the formula.
Mosteller Formula (preferred)
BSA (m²) = √[(Height cm × Weight kg) ÷ 3,600]
Example: 170 cm, 70 kg → √[(170 × 70) ÷ 3,600] = √3.306 ≈ 1.82 m²
DuBois Formula
BSA (m²) = 0.007184 × Height (cm)^0.725 × Weight (kg)^0.425
More complex to compute by hand; same result as Mosteller within ±2% for typical adults.
Applying BSA to a Drug Dose
Total Dose (mg) = Dose per m² (mg/m²) × BSA (m²)
Example: Carboplatin 400 mg/m² for a patient with BSA 1.82 m² → 400 × 1.82 = 728 mg
Normal adult BSA is approximately 1.7 m² (range roughly 1.5–2.2 m² for most adults). Protocols that set a BSA cap (e.g., max 2.0 m²) do so to prevent overdosing in obese patients — always check whether your institution's protocol applies a cap.
Quick Reference: BSA by Weight and Height
| Weight (kg) | Height (cm) | BSA Mosteller (m²) | BSA DuBois (m²) | Notes |
|---|---|---|---|---|
| 50 kg | 160 cm | 1.52 | 1.52 | Small adult |
| 60 kg | 165 cm | 1.67 | 1.66 | Average female |
| 65 kg | 168 cm | 1.75 | 1.74 | Average female |
| 70 kg | 170 cm | 1.82 | 1.81 | Average adult |
| 75 kg | 173 cm | 1.90 | 1.89 | Average male |
| 80 kg | 175 cm | 1.97 | 1.96 | Average male |
| 90 kg | 180 cm | 2.12 | 2.11 | Larger adult |
| 100 kg | 183 cm | 2.26 | 2.25 | Large adult |
BSA values calculated using Mosteller formula; DuBois values are approximated. Always recalculate from the patient's actual current measurements.
Frequently Asked Questions
Why is BSA used for chemotherapy dosing?
Body surface area is used for chemotherapy because many cytotoxic drugs have narrow therapeutic windows — a small overdose can be lethal, and an underdose may be ineffective. BSA correlates better than weight alone with cardiac output and renal clearance, which determine how quickly a drug is distributed and eliminated. By dosing per m², clinicians can achieve more consistent drug exposure across patients of different body sizes. Weight-based mg/kg dosing is less accurate for these drugs because organ function does not scale linearly with weight.
What is the Mosteller formula for BSA?
The Mosteller formula calculates BSA as: BSA (m²) = √[(Height in cm × Weight in kg) ÷ 3,600]. It is the most widely used formula in clinical practice due to its simplicity. For example, a patient who is 170 cm tall and weighs 70 kg: BSA = √[(170 × 70) ÷ 3,600] = √[11,900 ÷ 3,600] = √3.306 ≈ 1.82 m². The DuBois formula (BSA = 0.007184 × Height^0.725 × Weight^0.425) is an older, more complex formula that gives similar results.
What is a normal BSA for adults?
The average BSA for adult men is approximately 1.9 m² and for adult women approximately 1.6 m². A commonly referenced average for adults of both sexes is 1.7 m². Newborns have a BSA of about 0.25 m², and a 10-year-old child is approximately 1.14 m². Oncology protocols often use 1.7–1.8 m² as a starting reference when actual measurements are not available, though calculating from the individual patient's actual height and weight is always preferred.