Height + weight
→ BSA (m²)
Calculate body surface area in m² from height and weight using the formula named by the relevant protocol or reference.
Use when: Your source asks for BSA or an m² value.
Calculate BSAWhich body measure do you need?
Use the body measure explicitly named by the medicine reference, protocol or equation. BSA, ideal body weight and adjusted body weight are different calculation tools and are not interchangeable.
BSA → m²Devine IBW → kg0.4 AdjBW → kg
Calculate now
What does your clinical source ask for?
Choose the calculator that returns the exact body measure named by the medicine reference, protocol or equation you are following.
Height + Devine equation
→ IBW (kg)
Calculate adult Devine ideal body weight when the clinical source specifically requires IBW as its reference weight.
Use when: Your source explicitly asks for Devine IBW.
Calculate IBWActual weight + IBW
→ AdjBW (kg)
Calculate the 0.4 adjusted-body-weight method from actual weight and Devine IBW when a clinical source explicitly requires it.
Use when: Your source explicitly asks for the 0.4 AdjBW method.
Calculate AdjBWThe source chooses the body measure
Do not substitute actual weight, BSA, ideal body weight or adjusted body weight for one another. Use the measure and equation explicitly required by the governing medicine reference, protocol or calculation method.
Need more than the calculator?
Go further
Understand
Body measure Guides
Compare BSA, IBW and adjusted body weight and understand when each method is used.
OpenLearn
Specialised Dosing Calculations
Learn BSA dosing and other specialised medication-calculation systems.
OpenPractise
Body-measure dosing practice
Practise BSA dosing, then use the wider Practice library for related skills.
OpenSafety & checking
Do not let similar-looking body measures become interchangeable
Keep the named measure, equation and units attached to the result, and verify that the governing source actually requires that method.
Safety & checking
Do not let similar-looking body measures become interchangeable
Keep the named measure, equation and units attached to the result, and verify that the governing source actually requires that method.
1.Choosing the measure yourself
The medicine reference, protocol or equation should tell you whether to use actual weight, IBW, AdjBW, BSA or another descriptor.
2.Treating IBW as a healthy-weight target
Clinical IBW equations are calculation tools. They are not a general recommendation for what a person should weigh.
3.Assuming AdjBW is universal
The 0.4 adjusted-weight method is not a universal dosing rule. Use it only when the applicable source specifies that method.
4.Mixing BSA with other weight methods
BSA is reported in m² and is not interchangeable with BMI, mg/kg dosing or a body weight reported in kilograms.
Related
Continue around this topic
Body measure calculator FAQs
Answers about choosing BSA, IBW, or adjusted body weight without duplicating the individual calculator formulas.
Body measure calculator FAQs
Answers about choosing BSA, IBW, or adjusted body weight without duplicating the individual calculator formulas.
Which body measure calculator should I use?
Use the calculator that matches the body measure explicitly named by the medicine reference, protocol, equation, prescriber, pharmacist, or local policy.
- Choose BSA when the source asks for body surface area in m².
- Choose IBW when the source specifically asks for adult Devine ideal body weight.
- Choose AdjBW when the source specifically asks for the 0.4 adjusted-body-weight method.
What is the difference between BSA, IBW, and adjusted body weight?
They are different body-size descriptors used for different calculation jobs; they should not be treated as interchangeable.
- BSA is an area estimate reported in m² and is calculated from height and weight.
- Devine IBW is an adult reference-weight equation based mainly on height and the selected sex equation.
- The AdjBW calculator on MedMaths starts with Devine IBW and adds 40% of the difference between actual weight and IBW when the method applies.
Does MedMaths decide which dosing weight or body measure a medicine should use?
No. MedMaths calculates the body measure you select; it does not decide which measure is clinically appropriate for a medicine or patient.
- The correct body measure is source- and medicine-specific.
- If the required measure is unclear, verify it with the applicable reference or clinical team before calculating or administering a medicine.
Where can I compare the different BSA formulas?
Use the MedMaths BSA Formula Guide for the Mosteller, Du Bois, Haycock, and Gehan & George comparison; use the BSA Calculator when you need the number itself.
- The calculator performs the arithmetic for the selected equation.
- The Guide explains why the formulas differ and how to follow a protocol-specified formula.
Formula origins in this topic
The equations used in these calculators were developed by published researchers. These researchers are not affiliated with MedMaths and have not reviewed or endorsed this site.
Devine Ideal Body Weight Formula
Equation attributed to: Ben J. Devine
References
Background sources for body surface area, the Mosteller BSA equation and the Devine ideal-body-weight equations.
References
Background sources for body surface area, the Mosteller BSA equation and the Devine ideal-body-weight equations.
Body Surface Area
NCBI Bookshelf / StatPearls
Clinical overview of body surface area and its use in physiological and medication calculations.
Simplified Calculation of Body-Surface Area
New England Journal of Medicine
Robert Mosteller's 1987 publication proposing the simplified square-root BSA equation.
The Origin of the ‘Ideal’ Body Weight Equations
Annals of Pharmacotherapy / SAGE
Historical review of the equations commonly described as Devine ideal body weight formulas.