Body Surface Area (BSA) Calculator
Calculate BSA using the Mosteller, DuBois & DuBois, or Haycock formula. BSA is the standard metric for chemotherapy dose individualisation and is used widely in oncology, pharmacology, burns assessment, and renal and cardiac indexing.
Calculate Body Surface Area
Enter height and weight to calculate BSA. Select your preferred unit system and formula. The Mosteller formula is recommended for most clinical applications including chemotherapy dosing.
BSA is an estimation of total body surface area derived from height and weight. Different formulas produce slightly different results — variations of 5–10% between formulas are common. For consistency, the same formula should be used throughout a patient’s treatment course. Always confirm chemotherapy doses against institutional protocols and current prescribing information.
Understanding Body Surface Area
Body surface area is a geometric property of the human body that correlates with several physiological parameters more reliably than body weight alone. BSA scales with metabolic rate, blood volume, glomerular filtration rate, and cardiac output. This relationship underpins its use in drug dosing — particularly for cytotoxic chemotherapy — where the therapeutic window is narrow and dosing precision is critical.
The concept of using BSA for drug dosing dates to Pinkel’s 1958 observation that dose-limiting toxicities in children were better predicted by BSA than by weight. Since then, BSA-based dosing has become the dominant paradigm in oncology, despite ongoing debate about whether it truly improves dosing accuracy compared to flat-dosing or pharmacokinetically guided approaches.
Mosteller Formula (1987)
BSA = √(Heightcm × Weightkg ÷ 3600)
Example: 170 cm, 70 kg
= √(170 × 70 ÷ 3600)
= √3.306
= 1.82 m²
Most widely used. Simplest formula — easy bedside calculation. Recommended by ASCO and most oncology protocols.
DuBois & DuBois (1916)
BSA = 0.007184 × H0.725 × W0.425
Example: 170 cm, 70 kg
= 0.007184 × 1700.725 × 700.425
= 0.007184 × 44.57 × 6.40
= 1.81 m²
Original formula. Derived from only 9 subjects. May underestimate BSA at extremes of body weight. Still widely referenced.
Why Mosteller? The Mosteller formula produces values very close to DuBois at normal body weights but is simpler to calculate (requiring only a square root). It has become the de facto standard in most oncology protocols. The Haycock formula is preferred for neonates and young children because it was validated in a paediatric population (0–18 years). For consistency, the same formula should be used throughout a patient’s treatment course.
Interpretation & Reference Ranges
BSA values vary with age, sex, and body habitus. The table below provides typical adult and paediatric reference ranges. Note that BSA is a continuous variable — there are no rigid “normal” or “abnormal” categories. The clinical significance lies in how BSA is used (drug dosing, cardiac index, renal indexing) rather than the value itself.
| Population | Typical BSA (m²) | Notes |
|---|---|---|
| Neonate (3.5 kg) | 0.20–0.25 | Use Haycock formula. BSA-based dosing is standard for neonatal chemotherapy. |
| Infant (10 kg) | 0.45–0.50 | Haycock formula recommended. Proportionally larger surface area relative to weight than adults. |
| Child (30 kg) | 1.00–1.10 | Transition to adult-type proportions. BSA-based dosing is standard in paediatric oncology. |
| Adult female (average) | 1.60–1.80 | Based on average height ~163 cm and weight ~65 kg. Varies with body composition. |
| Adult male (average) | 1.80–2.00 | Based on average height ~175 cm and weight ~80 kg. Varies with body composition. |
| Obese adult (BMI >35) | 2.20–2.80+ | Consider BSA capping at 2.0 m² for some chemotherapy agents. Check institutional protocol. |
BSA in Clinical Indexing
The 1.73 m² convention: When eGFR is reported in mL/min/1.73 m², it has been normalised to a standard BSA. For patients with a BSA that differs significantly from 1.73 m² (e.g., BSA 2.4 in a large patient or 1.3 in a small elderly patient), the absolute GFR (un-indexed) should be calculated for drug dosing: Absolute GFR = eGFR × (patient BSA ÷ 1.73).
BSA & Chemotherapy Dosing
BSA-based dosing is the dominant paradigm in medical oncology. Most cytotoxic chemotherapy protocols express doses in mg/m² or units/m², with the intent of normalising drug exposure across patients of different body sizes. However, the relationship between BSA and drug clearance is imperfect, and there is growing evidence that BSA explains only a fraction of interpatient pharmacokinetic variability.
The standard workflow for chemotherapy dosing involves: (1) measuring the patient’s height and weight, (2) calculating BSA using the institutional formula of choice (usually Mosteller), (3) multiplying the protocol dose (mg/m²) by the BSA, and (4) rounding to the nearest practical dose increment.
For example, a protocol calling for doxorubicin 60 mg/m² in a patient with a BSA of 1.82 m² yields 60 × 1.82 = 109.2 mg. This would typically be rounded to 110 mg. Most institutions allow rounding within ±5% of the calculated dose without requiring formal dose modification.
Height is typically measured once (at baseline) while weight is measured before each cycle, as weight can fluctuate significantly during treatment. BSA should be recalculated for each cycle if weight has changed meaningfully (>5% from baseline).
Historically, many institutions capped BSA at 2.0 m² for chemotherapy dosing, regardless of the patient’s actual BSA. This practice arose from concern about increased toxicity in large patients, but it has no strong evidence basis. In fact, ASCO published guidelines in 2012 recommending full weight-based dosing (using actual body weight, uncapped BSA) for obese patients receiving curative-intent chemotherapy.
The rationale is that capping BSA effectively under-doses obese patients, potentially reducing efficacy without a demonstrated reduction in toxicity. Studies of breast cancer (CALBG 8541), colon cancer, and lymphoma have shown that dose reductions based on BSA capping are associated with worse outcomes.
However, some agents with high toxicity potential (e.g., vincristine, which is typically capped at 2 mg total regardless of BSA) and some palliative regimens may warrant dose modification. Always follow institutional protocols and consult oncology pharmacy for dose verification.
An increasing number of modern agents — particularly monoclonal antibodies, immune checkpoint inhibitors, and targeted therapies — use flat (fixed) dosing rather than BSA-based dosing. This shift is driven by pharmacokinetic evidence that BSA explains less than 15% of the interpatient variability in clearance for many drugs, and that flat dosing achieves comparable exposure distributions.
Examples of drugs that have transitioned to flat dosing include pembrolizumab (200 mg or 400 mg flat, rather than 2 mg/kg), nivolumab (240 mg or 480 mg flat), and atezolizumab (1200 mg flat). The practical advantages of flat dosing include reduced pharmacy preparation time, fewer dosing errors, and the ability to use pre-filled presentations.
For traditional cytotoxic chemotherapy (alkylating agents, anthracyclines, taxanes, platinum compounds), BSA-based dosing remains standard practice because these drugs have narrower therapeutic indices and greater toxicity related to exposure.
For some drugs, pharmacokinetic (PK) or pharmacodynamic (PD) monitoring provides more precise dose individualisation than BSA alone. The best-established example is carboplatin, which is dosed using the Calvert formula based on target AUC and measured or estimated GFR: Dose (mg) = Target AUC × (GFR + 25). This approach bypasses BSA entirely and accounts for renal function, which is the primary determinant of carboplatin clearance.
Therapeutic drug monitoring (TDM) with dose adjustment is used for methotrexate (high-dose regimens) and busulfan (pre-transplant conditioning). For 5-fluorouracil (5-FU), dose adjustment based on pharmacokinetically guided DPD activity testing or area under the curve monitoring has shown improved outcomes compared to fixed BSA-based dosing.
The future of oncology dosing is likely to move increasingly towards PK-guided approaches, genotype-guided dosing (e.g., DPYD testing before fluoropyrimidines, UGT1A1 testing before irinotecan), and fixed dosing for large-molecule agents, with BSA-based dosing remaining for traditional cytotoxics where better methods are not yet validated.
Always verify chemotherapy doses against institutional protocols, current prescribing information, and pharmacy systems. BSA calculation is only one step in the dosing workflow. Dose reductions for renal impairment, hepatic dysfunction, prior toxicity, performance status, and drug interactions must be applied separately. All chemotherapy orders should be independently verified by an oncology pharmacist.
Special Populations & Considerations
Clinical takeaway: BSA is a surrogate for body size, not a direct measure of drug clearance capacity. In patients at the extremes of body composition — obesity, sarcopenia, cachexia, significant oedema — BSA-based dosing may be inaccurate. Consider pharmacokinetically guided dosing, TDM, or dose adjustment based on first-cycle toxicity in these populations.
Common Pitfalls & Limitations
Different BSA formulas can produce results that vary by 5–10% in the same patient. The Mosteller and DuBois formulas agree closely at average body weights but diverge at extremes. Switching formulas between cycles can cause unintended dose fluctuations — a patient whose BSA is calculated as 1.85 m² by Mosteller and 1.78 m² by DuBois would receive a 4% dose difference for the same weight.
Institutions should standardise on a single formula and ensure all electronic prescribing systems, pharmacy software, and clinical calculators use the same one. The Mosteller formula is the most widely adopted standard.
Cancer patients frequently experience weight changes during treatment — from tumour response, appetite changes, fluid shifts, cachexia, or steroid-induced weight gain. Using a stale weight from the baseline visit can lead to under- or over-dosing. Best practice is to weigh the patient at each cycle visit and recalculate BSA if weight has changed by more than 5% from the last calculated value.
Height, in contrast, is typically measured once at baseline (adults don’t change height during treatment, and it is less prone to measurement variability).
BSA explains only 15–35% of interpatient variability in clearance for most cytotoxic drugs. Other factors — hepatic function, renal function, genetic polymorphisms (CYP2D6, UGT1A1, DPYD), drug interactions, protein binding, and body composition — often contribute more to pharmacokinetic variability than body size.
For drugs with a wide therapeutic index (most monoclonal antibodies), BSA-based dosing offers no meaningful advantage over flat dosing. For drugs where exposure matters critically (carboplatin, high-dose methotrexate, busulfan), PK-guided dosing methods are superior to BSA-based dosing. BSA-based dosing is a pragmatic compromise — it is simple, widely standardised, and “good enough” for most cytotoxics, but it is not precision dosing.
Empirical BSA capping at 2.0 m² remains entrenched at some institutions despite ASCO’s clear recommendation against this practice for curative-intent chemotherapy. Studies in breast cancer (CALBG 8541), colon cancer (NSABP), and DLBCL have consistently shown that dose reduction in obese patients is associated with inferior disease-free and overall survival.
The fear that full-weight dosing in obese patients leads to unacceptable toxicity has not been borne out in the evidence — toxicity rates in obese patients dosed by actual weight are comparable to those in non-obese patients. Dose reductions should be based on actual toxicity experienced, not on anticipated toxicity based on body weight.
Quick Reference Summary
| Formula | Expression | Best Used For |
|---|---|---|
| Mosteller | √(Hcm × Wkg ÷ 3600) | General use, oncology standard. Simplest formula. |
| DuBois & DuBois | 0.007184 × H0.725 × W0.425 | Historical standard. May underestimate at extreme weights. |
| Haycock | 0.024265 × H0.3964 × W0.5378 | Paediatric patients (validated 0–18 years). Preferred for neonates/infants. |
| Calvert (carboplatin) | Dose = AUC × (GFR + 25) | Carboplatin dosing. Uses GFR, not BSA. Target AUC typically 5–7. |
Use the same formula consistently, weigh the patient every cycle, and never cap BSA for curative-intent chemotherapy. BSA-based dosing is a standardised starting point — not a substitute for clinical judgement. Adjust for organ dysfunction, prior toxicity, performance status, and drug-specific protocols. When a superior dosing method exists (Calvert for carboplatin, TDM for methotrexate/busulfan), use it.
Disclaimer & References
For Educational Purposes Only. This calculator and the accompanying clinical information are intended as educational tools for healthcare professionals. They do not replace clinical judgement. Results should be interpreted in the full clinical context. Lab reference ranges vary by institution — verify with your own laboratory. Drug dosages should be confirmed against current prescribing information.
References
- Mosteller RD. Simplified calculation of body-surface area. New England Journal of Medicine. 1987;317(17):1098. DOI: 10.1056/NEJM198710223171717
- DuBois D, DuBois EF. A formula to estimate the approximate surface area if height and weight be known. Archives of Internal Medicine. 1916;17(6):863–871. DOI: 10.1001/archinte.1916.00080130010002
- Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults. Journal of Pediatrics. 1978;93(1):62–66. DOI: 10.1016/S0022-3476(78)80601-5
- Griggs JJ, Bohlke K, Balaban EP, et al. Appropriate chemotherapy dosing for obese adult patients with cancer: American Society of Clinical Oncology clinical practice guideline. Journal of Clinical Oncology. 2012;30(13):1553–1561. DOI: 10.1200/JCO.2011.39.9436
- Pinkel D. The use of body surface area as a criterion of drug dosage in cancer chemotherapy. Cancer Research. 1958;18(7):853–856.
- Calvert AH, Newell DR, Gumbrell LA, et al. Carboplatin dosage: prospective evaluation of a simple formula based on renal function. Journal of Clinical Oncology. 1989;7(11):1748–1756. DOI: 10.1200/JCO.1989.7.11.1748
- Gurney H. How to calculate the dose of chemotherapy. British Journal of Cancer. 2002;86(8):1297–1302. DOI: 10.1038/sj.bjc.6600139
- Baker SD, Verweij J, Rowinsky EK, et al. Role of body surface area in dosing of investigational anticancer agents in adults, 1991–2001. Journal of the National Cancer Institute. 2002;94(24):1883–1888. DOI: 10.1093/jnci/94.24.1883