Calculate body surface area (BSA) in m² from height and weight, compare Mosteller, Du Bois, Haycock, Gehan & George, and Boyd formulas, review formula spread.
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Body surface area calculator with formula comparison Estimate BSA in m² from height and weight, compare Mosteller, Du Bois, Haycock, Gehan & George, and Boyd formulas, scale a per-m² protocol value, or adjust a value indexed to 1.73 m².
Clinical-reference caution
For a general BSA check, compare formulas and keep the same method when tracking repeated estimates.
BSA can support dosing or indexed physiology checks, but it should not be used to self-prescribe or adjust treatment.
Body surface area
1.82 m²
Primary estimate uses the Mosteller formula.
1.82 m²
Average across five formulas
1.37%
Formula spread
1.05×
Relative to 1.73 m²
24.22
BMI context
Formula
BSA
Use note
Mosteller
1.82 m²
Simple default used by many clinical calculators.
Du Bois
1.81 m²
Classic historical equation from height and weight.
Haycock
1.83 m²
Common comparator for pediatric and mixed-age contexts.
Gehan & George
1.83 m²
Frequently included in multi-formula BSA comparisons.
Boyd
1.83 m²
Older weight-sensitive equation used in some reference tools.
Converted inputs: 170 cm and 70 kg.
Formula sensitivity: the five equations differ by 0.02 m² for these inputs. Keep the formula consistent when tracking repeated results.
Body surface area calculator: BSA formulas, m² results, and clinical context
A body surface area calculator estimates the total outer surface of the body in square metres using height and weight. This page also explains the main assumptions behind the body surface area calculator result, highlights the supporting figures shown by the calculator, and helps the reader use the estimate without overstating what a quick online tool can prove.
What body surface area is measuring
Body surface area, usually abbreviated as BSA, is an estimate of the total area of the human body’s external surface. In practice it is not measured directly for everyday clinical use. Instead, it is estimated from height and weight using a mathematical formula. That is why a body surface area calculator in m² usually asks for only those two inputs.
BSA is still used in a range of medical settings, especially where body size affects dosing, equipment settings, or physiological comparison. It is most familiar in chemotherapy dosing, but it also appears in burn assessment, paediatric dosing contexts, and some cardiology and nephrology references. Even so, BSA is an estimate, not a directly measured physical constant for the person sitting in front of the calculator.
Core body surface area formulas
The live calculator shows five established BSA equations. Mosteller is popular because it is easy to calculate. Du Bois is one of the oldest and most historically cited equations. Haycock is often discussed because it has been used in paediatric settings and in comparisons against measured surface area. Gehan & George and Boyd are included because strong clinical calculator references often show them when the user needs a wider formula comparison.
Mosteller: BSA = √((height in cm × weight in kg) / 3600)
The Mosteller equation is a simplified body surface area formula and is often used in practice because it is easy to compute.
Du Bois: BSA = 0.007184 × height(cm)^0.725 × weight(kg)^0.425
The Du Bois equation is one of the classic historical formulas for estimating BSA from height and weight.
The Boyd equation uses weight in grams and a self-adjusting exponent, so it can diverge from simpler formulas in some body-size ranges.
Worked example: BSA from height and weight
For a person who is 170 cm tall and weighs 70 kg, the Mosteller formula calculates BSA as √((170 × 70) / 3600), or about 1.82 m². The Du Bois formula gives about 1.81 m², Haycock gives about 1.83 m², Gehan & George gives about 1.83 m², and Boyd gives about 1.83 m² for the same inputs.
Those answers are close, but they are not identical. The calculator therefore shows the selected primary formula, the average across formulas, and the formula spread. This makes it easier to see whether the difference is trivial for a general reference check or important enough that the exact protocol formula should be confirmed before using the number.
If a protocol value is entered as an amount per m², the calculator multiplies that value by the selected BSA. That output is a scaling example only. Real medication or treatment decisions may also require rounding rules, dose caps, organ-function adjustments, current lab data, age-specific rules, and clinician review.
Why different formulas give slightly different answers
Different BSA equations were derived from different samples and measurement methods, so small differences between formulas are normal. In an average-sized adult, those differences are often modest, but they can matter more at the extremes of height, weight, age, or body shape. That is why some clinical references specify which equation should be used rather than simply asking for “body surface area.”
This also explains why a body surface area calculator should be treated as a reference tool rather than an absolute body-size truth. If a treatment protocol or research paper specifies Mosteller, it is better to use Mosteller consistently than to switch formulas between visits.
Mosteller is commonly used because it is simple and fast to calculate.
Du Bois remains widely cited because of its historical role in clinical practice.
Haycock is often referenced in paediatric and comparative validation work.
Formula consistency matters more than chasing a tiny difference between methods in routine use.
Which BSA formula should you choose?
For quick educational use, Mosteller is often the most practical default because it is transparent and easy to audit by hand. Many calculators and clinical teaching materials use it for that reason. However, the best formula is not always the simplest one; it is the one required by the protocol, institution, research paper, or dosing reference you are trying to follow.
Du Bois may appear in older references and long-running clinical systems. Haycock is commonly cited in paediatric and mixed-age contexts. Gehan & George and Boyd appear in broader formula comparisons. If a page, prescription, chart, or protocol names a formula, use that formula consistently rather than switching to a different equation because it produces a slightly more convenient number.
Formula spread is most useful as a quality-control signal. If all formulas are close, the BSA estimate is relatively stable for the entered height and weight. If the spread grows, especially at extremes of size or altered body composition, that is a cue to verify the intended method before using the result for any medical calculation.
A body surface area result is most useful when the surrounding medical context is clear. It can help with dose calculations, protocol checks, and comparing values that are normalized to m², but it is not a full assessment of health, fitness, or body composition. A higher or lower BSA simply reflects body size as captured by the chosen equation.
For general users, this calculator works best as a reference and estimation tool. For medical decisions, use the same formula required by the relevant protocol and rely on clinician review where dosing or treatment safety is involved. A free body surface area calculator online is useful because it makes the arithmetic easy, but it does not replace clinical judgement.
The optional indexed-value field is for values that are explicitly reported against a standard BSA of 1.73 m², such as some kidney-function or physiology references. Multiplying the indexed value by the selected BSA and dividing by 1.73 gives an arithmetic body-size adjustment, but the clinical meaning still depends on the test, protocol, and clinician interpretation.
NCBI Bookshelf — Body Surface Area — Current clinical review summarising where BSA is used, why formula choice matters, and the limitations of BSA-based dosing.
Body surface area (BSA) is primarily used in clinical settings to calculate drug doses, particularly for chemotherapy agents where dosing by weight alone would under- or over-dose patients at the extremes. It is also used to calculate burn coverage and haemodynamic parameters.
Which formula is most accurate?
The DuBois and DuBois formula (1916) is historically the most widely used. The Mosteller formula (1987) is simpler and nearly as accurate for most adults. The Haycock formula is preferred for paediatric patients. No formula is exact for all body types.
Can I use BSA to compare individuals of different sizes?
BSA normalises physiological variables by body size. Cardiac output, glomerular filtration rate, and metabolic rate can all be expressed per square metre of BSA, making comparisons between people of different sizes more meaningful than using absolute values.
What is the Mosteller formula for body surface area?
The Mosteller formula is BSA = √((height in cm × weight in kg) / 3600). It is widely used because it is easy to calculate and usually gives a result close to more complex height-weight formulas for many adults.
Why does this BSA calculator show more than one formula?
Different BSA equations were derived from different study populations and mathematical fits. Showing Mosteller, Du Bois, Haycock, Gehan & George, and Boyd side by side helps you see whether formula choice changes the result enough to matter for the context you are checking.
What does a normal body surface area mean?
There is no single clinical cut-off that makes BSA normal or abnormal. Many adult references cluster around roughly 1.7 m², but body surface area mainly reflects height and weight. Interpretation depends on why the value is being used.
Can this calculator be used for chemotherapy dosing?
It can show the arithmetic behind a BSA-based scaling example, but it should not be used to self-dose chemotherapy or adjust any treatment. Oncology dosing may involve protocol-specific formulas, dose caps, rounding rules, organ-function adjustments, toxicity history, and clinician verification.
Should I use actual weight, ideal weight, or adjusted weight for BSA?
Use the weight basis required by the protocol or clinician. Many simple BSA formulas use actual height and actual weight, but some medical contexts may specify a different weight basis, especially when body composition or body-size extremes are relevant.
How precise should a BSA result be?
Most BSA values are displayed to two decimal places because the formulas themselves are estimates. Avoid over-interpreting tiny differences between formulas unless the protocol you are following has explicit rounding or threshold rules.
Is BSA the same as BMI?
No. BMI is weight divided by height squared and is used as a broad body-size classification metric. BSA estimates external body surface area in square metres and is used for scaling some clinical values, dosing references, and physiological measurements.
What does per 1.73 m² mean in a BSA calculator?
Some physiology and kidney-function values are indexed to a standard body surface area of 1.73 m² so people of different sizes can be compared on the same scale. If a value is explicitly reported per 1.73 m², the calculator can show the arithmetic adjustment to the selected BSA, but the clinical interpretation still belongs with the relevant test, protocol, or clinician.
