Adjusted Body Weight Calculator
Compute adjusted body weight (AjBW) the way dietitians and pharmacists do: Devine ideal body weight plus 40% of the excess. Enter sex, height (inches or cm), and actual weight (lb or kg) to get AjBW, IBW, and your percent of IBW.
Example: with Sex Female · Height 64 · Height unit inches (5 ft 4 in = 64 in) · Actual weight 200 · Weight unit lb (pounds) → Adjusted body weight (AjBW): 152.4 lb (69.1 kg).
- Ideal body weight (Devine)120.6 lb (54.7 kg)
- Percent of IBW166% of IBW
- When AjBW appliesAt 120% of IBW or more, AjBW is commonly used for weight-based dosing and calorie math
Computed by the calculator below using its default values. Change any input to see your own numbers.
AjBW = IBW + 0.4 × (actual − IBW), with IBW from the Devine formula. Used because lean tissue — not fat — drives most drug distribution and calorie needs.
Why adjusted body weight exists
Weight-based math — drug doses, protein targets, calorie estimates — assumes weight is mostly lean, metabolically active tissue. In significant obesity that assumption breaks: adipose tissue takes up some drugs and burns some energy, but much less than muscle and organs do. Dosing on total weight overshoots; dosing on ideal weight undershoots. Adjusted body weight splits the difference by counting the ideal weight fully and the excess at 40%.
The 0.4 correction factor is a clinical convention, not a measured constant — some protocols use 0.3 or 0.5 for specific drugs. This calculator uses the classic 0.4 seen in aminoglycoside dosing and nutrition-support references, applied on top of the 1974 Devine ideal-weight formula.
Reading your result
AjBW only means something when actual weight is meaningfully above ideal — most references start applying it around 120% to 125% of IBW. Below that, clinicians generally just use actual weight, and if you weigh less than your IBW, actual weight is always the number to use. The percent-of-IBW line tells you which situation you are in.
How it’s calculated
IBW (Devine 1974): men 50 kg + 2.3 kg per inch over 5 ft; women 45.5 kg + 2.3 kg per inch over 5 ft. AjBW = IBW + 0.4 × (actual kg − IBW), applied only when actual weight exceeds IBW. Conversions: 1 lb = 0.45359237 kg; 1 in = 2.54 cm. Percent of IBW = actual ÷ IBW × 100.
This is an educational estimate, not medical advice — the 0.4 factor and even the choice of AjBW vs actual or ideal weight vary by drug and protocol, so confirm any dosing or clinical nutrition decision with a pharmacist, dietitian, or physician.
Devine ideal body weight by height
| Height | IBW — women | IBW — men |
|---|---|---|
| 5 ft 0 in | 100.3 lb (45.5 kg) | 110.2 lb (50.0 kg) |
| 5 ft 4 in | 120.6 lb (54.7 kg) | 130.5 lb (59.2 kg) |
| 5 ft 8 in | 140.9 lb (63.9 kg) | 150.8 lb (68.4 kg) |
| 6 ft 0 in | 161.2 lb (73.1 kg) | 171.1 lb (77.6 kg) |
Computed with the Devine formula: 45.5 kg (women) or 50 kg (men) + 2.3 kg per inch over 60 in; rounded to 0.1.
Common mistakes
- Using AjBW when actual weight is below or near IBW — the adjustment is only for weight well above ideal, typically 120%+ of IBW.
- Applying the 0.4 factor to total weight instead of only the excess above IBW.
- Forgetting Devine works in kilograms and inches — mixing in pounds without converting inflates everything.
- Treating 0.4 as universal: some drugs use 0.3, others use total or ideal weight; the protocol wins.
Frequently asked questions
What is the adjusted body weight formula?
AjBW = IBW + 0.4 × (actual weight − IBW), in kilograms. IBW comes from the Devine formula: 50 kg + 2.3 kg per inch over 5 feet for men, 45.5 kg + 2.3 for women. Example: a 5 ft 4 in woman weighing 200 lb has IBW 54.7 kg and AjBW about 69.1 kg (152 lb).
When should adjusted body weight be used instead of actual weight?
Convention is when actual weight exceeds roughly 120% to 125% of ideal body weight. Below that, weight-based calculations usually just use actual weight; below IBW, always use actual weight.
Why 40% of the excess weight?
Excess weight is not inert — adipose tissue and its supporting lean mass carry some metabolic and drug-distribution activity, just less than lean tissue. Studies behind the convention put that contribution around 20% to 40% depending on the drug, and 0.4 became the standard compromise.
Is AjBW the same as lean body mass?
No. Lean body mass is measured or estimated body composition (everything except fat). AjBW is a dosing construct: ideal weight plus a fraction of the excess. They can be numerically close but answer different questions.
Can I dose medication from this number?
Not on your own. Which weight to use (actual, ideal, adjusted, or lean) is drug-specific, and getting it wrong matters. Use this to understand the math, then let a pharmacist or physician pick the weight for any real dose.