Body Surface Area Calculator - Free BSA Medical Calculator for Chemotherapy Dosing and Dialysis (No Sign-up Required)
Body Measurements
Enter age for appropriate BSA reference ranges
Standing height measurement
Body weight measurement
What is BSA?
Body Surface Area (BSA) is the measured or calculated surface area of a human body. It's used in medicine to calculate drug dosages, medical indicators, and other clinical measures.
BSA Calculation Results
Enter your measurements and click "Calculate BSA" to see your results
Understanding Body Surface Area (BSA) in Medicine
Body Surface Area (BSA) is the measured or calculated surface area of a human body, typically expressed in square meters (m²). BSA is one of the most important measurements in clinical medicine, particularly for calculating accurate drug dosages, assessing burn injuries, and normalizing cardiac output. Unlike simple weight-based dosing, BSA accounts for both height and weight, providing a more accurate reflection of metabolic mass and medication distribution.
Why BSA is Important in Medicine
BSA-based dosing is critical because it:
- Improves medication safety: Prevents under or overdosing, especially in chemotherapy
- Accounts for body composition: Better reflects metabolic capacity than weight alone
- Standardizes across populations: Enables comparison between children, adults, and different body types
- Reduces toxicity risk: Particularly important for narrow therapeutic index drugs
- Optimizes efficacy: Ensures adequate drug exposure for therapeutic effect
BSA Formulas Explained
Multiple formulas have been developed to calculate BSA. Our calculator includes all 8 major validated formulas:
1. Du Bois Formula (1916)
History: The original and most widely recognized formula, published in 1916.
Use: Traditional standard for clinical calculations.
Accuracy: Validated across broad populations, slightly overestimates at extremes.
2. Mosteller Formula (1987)
History: Simplified formula developed in 1987.
Use: FDA-recommended for clinical trials, easiest to calculate.
Accuracy: Highly accurate, agrees closely with Du Bois formula.
3. Haycock Formula (1978)
History: Developed for infants and children.
Use: Preferred for pediatric populations.
Accuracy: More accurate for children than Du Bois.
4. Gehan & George (1970)
History: Derived from direct measurements.
Use: Validated across wide weight range (0.8-150 kg).
Accuracy: Very accurate for both children and adults.
5. Boyd Formula (1935)
History: Complex formula using logarithmic adjustment.
Use: Research applications.
Accuracy: Good, but complex to calculate manually.
6. Fujimoto Formula (1968)
History: Developed in Japan for Asian populations.
Use: May be more accurate for Asian body types.
Accuracy: Good for intended population.
7. Takahira Formula (1925)
History: Japanese modification of Du Bois.
Use: Alternative to Du Bois.
Accuracy: Very similar to Du Bois results.
8. Schlich Formula (2010)
Female: 0.000975482 × H0.46 × W0.78
History: Modern gender-specific formula (2010).
Use: Most recent formula, gender-adjusted.
Accuracy: May be most accurate for modern populations.
⚠️ Formula Selection Guidelines
- Most clinical settings: Mosteller or Du Bois (most widely accepted)
- Pediatric patients: Haycock, Gehan & George, or Mosteller
- Clinical trials: Mosteller (FDA recommended)
- Asian populations: Fujimoto or Takahira may be more accurate
- Gender considerations: Schlich formula accounts for gender differences
- In practice: Differences between formulas are usually <5%, any validated formula is acceptable
Clinical Applications of BSA
💊 Oncology: Chemotherapy Dosing
BSA-based dosing is the gold standard for most chemotherapy agents. Most antineoplastic drugs are dosed in mg/m² to minimize toxicity while maintaining efficacy.
How to calculate chemotherapy dose:
- Calculate patient's BSA using validated formula (Mosteller recommended)
- Identify prescribed dose in mg/m² from protocol (e.g., Doxorubicin 50 mg/m²)
- Multiply: Total Dose = BSA × mg/m² dose
- Example: 1.85 m² × 50 mg/m² = 92.5 mg total dose
Common chemotherapy agents dosed by BSA:
- • Doxorubicin (Adriamycin): 60-75 mg/m² every 21 days
- • Cisplatin: 50-120 mg/m² every 3-4 weeks
- • 5-Fluorouracil (5-FU): 400-600 mg/m² IV bolus
- • Carboplatin: Target AUC (area under curve) using Calvert formula
- • Paclitaxel: 175-250 mg/m² every 3 weeks
- • Docetaxel: 60-100 mg/m² every 3 weeks
⚠️ Always verify calculations, check for dose modifications (renal/hepatic impairment, obesity, elderly), and follow institutional protocols. Two-provider verification is standard practice.
🩸 Nephrology: Dialysis and Renal Function
BSA is used to normalize renal function measurements and optimize dialysis treatment.
Glomerular Filtration Rate (GFR) Indexing
eGFR is often reported "indexed" to BSA of 1.73 m² (average adult BSA) to standardize results. Actual GFR = Indexed GFR × (Patient BSA / 1.73).
Dialysis Blood Flow Rates
Blood flow rate during hemodialysis: 250-300 mL/min × (BSA/1.73). For BSA 1.85 m²: 267-320 mL/min recommended.
Kt/V Calculation (Dialysis Adequacy)
Target Kt/V ≥1.2 for adequate hemodialysis. BSA is used to estimate urea distribution volume (V).
🔥 Critical Care: Burn Assessment
BSA is critical for calculating burn extent and fluid resuscitation requirements.
Rule of Nines (% BSA burned)
Adult:
- • Head: 9%
- • Each arm: 9% (×2 = 18%)
- • Chest: 9%
- • Abdomen: 9%
- • Upper back: 9%
- • Lower back: 9%
- • Each leg: 18% (×2 = 36%)
- • Genitalia: 1%
Child (modified):
- • Head: 18% (larger head)
- • Each arm: 9%
- • Chest: 9%
- • Abdomen: 9%
- • Upper back: 9%
- • Lower back: 9%
- • Each leg: 13.5% (shorter legs)
Parkland Formula (Fluid Resuscitation)
Give half in first 8 hours, remaining half over next 16 hours. Example: 80 kg patient with 30% BSA burns: 4 × 80 × 30 = 9,600 mL Lactated Ringer's (4,800 mL in first 8h, 4,800 mL over next 16h).
💚 Cardiology: Cardiac Index
Cardiac Index (CI) normalizes cardiac output to BSA for comparison across different body sizes.
Normal CI: 2.5-4.0 L/min/m²
Example: Cardiac output 5.5 L/min, BSA 1.85 m² → CI = 5.5/1.85 = 2.97 L/min/m² (normal)
CI <2.2 suggests low cardiac output (heart failure, shock). CI >4.2 may indicate hyperdynamic state (sepsis, hyperthyroidism, anemia).
Special Populations and BSA Considerations
👶 Pediatric Patients
- •Formula choice: Haycock or Mosteller preferred
- •Dose caps: Some drugs have pediatric maximum doses even with BSA calculation
- •Neonates: Extra caution, may need specialized formulas or weight-based dosing
- •Growth: Recalculate BSA regularly as child grows
- •Verification: Always have two providers verify pediatric chemotherapy doses
🏋️ Obese Patients
- •BSA vs weight: BSA increases with obesity but not proportionally
- •Chemotherapy dosing: ASCO guidelines recommend using actual body weight for BSA (no capping)
- •BSA cap: Some institutions cap BSA at 2.0-2.5 m² to limit toxicity
- •Alternative: Consider ideal body weight or adjusted body weight for certain drugs
- •Monitoring: Watch for increased toxicity, may need dose reduction
👴 Elderly Patients
- •Physiology: Decreased lean body mass, altered drug metabolism
- •Renal function: Check creatinine clearance, may need dose reduction
- •Tolerance: May not tolerate full BSA-based doses, start lower
- •Frailty: Consider performance status, not just BSA
- •Polypharmacy: Watch for drug interactions
🤰 Pregnant Patients
- •Weight changes: Use pre-pregnancy weight or adjust for pregnancy weight
- •Blood volume: Increased during pregnancy, may affect drug distribution
- •Drug selection: Many chemotherapy agents contraindicated in pregnancy
- •Specialist consult: Maternal-fetal medicine and oncology collaboration essential
Safety Checklist for BSA-Based Dosing
🚨 Critical Safety Steps
- 1.Verify measurements: Confirm height and weight are current and accurate. Recheck if values seem unusual.
- 2.Calculate BSA correctly: Use validated formula (Mosteller recommended). Double-check calculation or use calculator.
- 3.Verify dose from protocol: Confirm the mg/m² dose from institutional protocol or drug monograph.
- 4.Calculate total dose: Total dose = BSA × mg/m² dose. Show your work.
- 5.Check for dose modifications: Adjust for renal/hepatic impairment, obesity (per guidelines), elderly, prior toxicity.
- 6.Independent verification: Have second qualified provider verify all calculations independently.
- 7.Check maximum dose: Some drugs have maximum dose limits regardless of BSA (especially pediatrics).
- 8.Verify final dose makes sense: Does it fall within expected range? Too high or too low may indicate error.
- 9.Document everything: Record BSA, dose calculation, modifications, verification in patient chart.
- 10.When in doubt, consult: Pharmacist, oncologist, or specialist. Never guess with chemotherapy dosing.
Common Mistakes to Avoid
❌ Using wrong units
Always verify if height should be in cm or inches, weight in kg or lbs. Converting incorrectly can lead to massive dosing errors. Our calculator handles conversions automatically.
❌ Outdated measurements
Recalculate BSA if patient has significant weight change (>10%) or for growing children. Don't rely on BSA from months ago.
❌ Forgetting dose modifications
Standard BSA calculation must be adjusted for renal failure, hepatic impairment, prior toxicity, and sometimes obesity or elderly. Check protocol for modifications.
❌ No independent verification
Chemotherapy errors can be fatal. Always have a second qualified provider independently verify BSA and dose calculations. This is standard of care.
❌ Confusing mg/m² with mg/kg
These are completely different! mg/m² requires BSA calculation, mg/kg uses weight directly. Mixing them up results in massive under or overdosing.
✅ Best Practices Summary
- ✓Use Mosteller or Du Bois formula (most widely accepted)
- ✓Verify current height and weight measurements
- ✓Always have independent verification of chemotherapy doses
- ✓Check for dose modifications (renal, hepatic, elderly, obesity)
- ✓Use institutional protocols and drug monographs
- ✓Document all calculations in patient chart
- ✓Recalculate BSA with significant weight changes
- ✓Consult pharmacy or specialist when uncertain
📚 Further Reading & References
- •Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098.
- •Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Int Med. 1916;17:863.
- •American Society of Clinical Oncology. Chemotherapy Dosing in Obese Adults: Guideline. J Clin Oncol. 2012.
- •FDA Guidance for Industry. Estimating the Maximum Safe Starting Dose in Initial Clinical Trials.