BMI, BSA, ideal and adjusted body weight calculator

Calculates body mass index, body surface area (Mosteller), ideal body weight (Devine) and adjusted body weight from height, weight and sex.

For healthcare professionals. Runs on your device. Nothing you enter is saved or sent.

Body size: BMI, BSA, IBW, AdjBW

When this estimate is not valid

BMI does not separate fat from muscle and can misclassify athletes, older adults and some ethnic groups.
The Devine IBW was described for adults; it is not validated under 152.4 cm (60 in) or in children.
Several BSA formulas exist; check which one a protocol specifies.
Under 18 years, BMI is interpreted with age- and sex-specific percentiles, not adult cut-offs.

Estimate only. Interpret it with the patient's clinical picture and the product label.

How it is calculated

BMI = weight (kg) ÷ height (m)²

Body mass index, shown to one decimal.

BSA = √(height (cm) × weight (kg) ÷ 3600)

Body surface area (Mosteller), in m², shown to two decimals.

IBW = 50 (men) or 45.5 (women) + 2.3 × (height in inches − 60)

Ideal body weight (Devine): 50 kg for men or 45.5 kg for women, plus 2.3 kg for every inch of height over 60 inches (152.4 cm). It needs sex and a height of at least 120 cm; under 152.4 cm the formula is not validated and a warning is shown.

AdjBW = IBW + 0.4 × (actual weight − IBW)

Adjusted body weight. It is normally used only when actual weight is above IBW.

Weight can be entered in kg or lb and height in cm or inches. Limits: weight 2–300 kg, height 45–230 cm.

Worked example

Height 170 cm, weight 70 kg:

70 ÷ 1.7² = 24.2 kg/m²
√(170 × 70 ÷ 3600) = 1.82 m²

BMI 24.2 kg/m², body surface area 1.82 m².

A man 180 cm tall weighing 80 kg (180 cm = 70.87 in):

50 + 2.3 × (70.87 in − 60) = 75.0 kg
75.0 + 0.4 × (80 − 75.0) = 77.0 kg

Ideal body weight 75.0 kg, adjusted body weight 77.0 kg.

Questions

Which BSA formula does this use?

Mosteller (1987): √(height in cm × weight in kg ÷ 3600). Other formulas, such as DuBois, give slightly different values; check which one a chemotherapy or dosing protocol specifies.

When is adjusted body weight used?

Adjusted body weight is used for some drugs in people whose actual weight is well above ideal body weight, for example in some aminoglycoside dosing and creatinine clearance calculations. The 0.4 factor is the one most often used; check the protocol for the drug.

Can ideal body weight be used for children or short adults?

The Devine formula was described for adults. It is not validated for heights under 152.4 cm (5 ft) or for children: the calculator shows a warning under 152.4 cm and no ideal body weight under 120 cm.

Does BMI measure body fat?

No. BMI does not separate fat from muscle and can misclassify athletes, older adults and some ethnic groups.

References

Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098. DOI 10.1056/NEJM198710223171717 PubMed 3657876
Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650–655. Not indexed in PubMed

Formula version: BMI · Mosteller 1987 · Devine 1974 · MediHelp calc v1.0.1

Formula and sources checked on 2026-10-29