Dosing
Ideal body weight calculator
Estimate ideal body weight (IBW) with the Devine formula from sex and height — then add an actual weight to get adjusted body weight for dosing. Enter metric or imperial units and see the full worked setup behind the answer. Free, no signup, runs in your browser.
Interactive calculator
Ideal body weight (IBW) calculator
Choose sex and enter height — in metric or imperial units — to estimate ideal body weight with the Devine formula. Add an actual weight to also get adjusted body weight. Results update as you type.
Result
Enter sex and height to see ideal body weight and the worked setup.
For education and practice only. This tool is a study aid, not a substitute for clinical judgment, a drug reference, or institutional policy. IBW is a dosing and reference estimate — not a goal or healthy weight — and weight-based dosing requires an independent double-check before administering.
How it works
The Devine formula
Introduced by Devine in 1974 for drug dosing, this is the most widely used IBW estimate. It starts from a base weight at 5 ft and adds a fixed amount for every inch of height above that — a simple rule that is easy to compute at the bedside.
Ideal body weight (kg)
Male: 50 + 2.3 × (in over 60) · Female: 45.5 + 2.3 × (in over 60)
Start from the base (50 kg male, 45.5 kg female) and add 2.3 kg for each inch of height above 5 ft (60 in). The formula is defined for heights over 60 in; at or below 60 in, use the base value only.
Adjusted body weight & conversions
AdjBW = IBW + 0.4 × (actual − IBW) · in = cm ÷ 2.54
Adjusted body weight nudges IBW upward when actual weight is higher — used for some drugs in obesity. Height in centimeters is converted to inches first (cm ÷ 2.54); 5 ft = 60 in. This calculator does the conversion and shows it in the steps.
Worked example
An IBW calculation, step by step
The patient
A male patient who is 70 inches (5 ft 10 in) tall, with an actual weight of 100 kg. What are his IBW and adjusted body weight?
The setup
- 1. Inches over 60: 70 − 60 = 10.
- 2. IBW = 50 + 2.3 × 10 = 50 + 23 = 73 kg.
- 3. AdjBW = 73 + 0.4 × (100 − 73) = 73 + 0.4 × 27 = 73 + 10.8.
- 4. = 83.8 kg.
Answer: IBW 73 kg · adjusted body weight 83.8 kg.
Reading the result
His actual weight (100 kg) is well above his IBW (73 kg), so a drug that is dosed on adjusted body weight would use 83.8 kg — between the two. A drug dosed on IBW alone would use 73 kg, and one dosed on actual weight would use 100 kg. The order and drug reference specify which weight applies.
Enter male, 70 in, and 100 kg in the calculator above to see this exact worked setup returned. Switch height to cm (177.8 cm ≈ 70 in) to see the conversion step.
Remember: 73 kg is a dosing reference for this height, not a goal weight for the patient.
Common questions
Ideal body weight, explained
- What is ideal body weight and why is it used?
- Ideal body weight (IBW) is a height- and sex-based weight estimate used as a reference for clinical calculations — not a personal target. It is used for weight-based dosing of certain drugs (some aminoglycosides and others are dosed on IBW rather than actual weight) and to set lung-protective ventilator tidal volumes, which are based on predicted body weight from height. It gives a consistent size estimate that does not swing with body fat.
- How does the Devine formula work?
- The Devine formula starts from a base weight at 5 ft (60 in) and adds 2.3 kg for each inch above that. For males: IBW (kg) = 50 + 2.3 × (inches over 60). For females: IBW (kg) = 45.5 + 2.3 × (inches over 60). For example, a male 70 in tall has 70 − 60 = 10 inches over 60, so IBW = 50 + 2.3 × 10 = 73 kg. Height in centimeters is converted first (cm ÷ 2.54 = inches).
- What is the difference between IBW and adjusted body weight?
- IBW is the height-and-sex estimate from the Devine formula. Adjusted body weight (AdjBW) corrects it upward for people whose actual weight is well above IBW, because some of that extra tissue still affects drug distribution: AdjBW = IBW + 0.4 × (actual weight − IBW). It is only meaningful when actual weight is above IBW, and it is used for dosing certain drugs in obesity where neither IBW nor actual weight alone fits.
- When is adjusted body weight used instead of IBW or actual weight?
- Adjusted body weight is used for selected medications in patients whose actual weight is substantially above IBW — the drug reference or protocol will specify which weight to use. The 0.4 factor assumes about 40% of the excess weight over IBW contributes to the drug's volume of distribution. Always follow the specific drug reference and institutional policy; the correct weight to use varies by medication.
- Is ideal body weight a goal or healthy weight?
- No. Despite the name, IBW is not a weight-loss target or a measure of health. It is a dosing and reference estimate derived only from height and sex, and it does not account for body composition, muscle mass, or overall health. Do not treat the number as a goal weight — use BMI and clinical assessment for questions about healthy weight instead.
- Does the formula work for people shorter than 5 feet?
- The Devine formula is defined for heights over 5 ft (60 in) — the '2.3 kg per inch over 60' term. At or below 60 in it simply returns the base value (50 kg male, 45.5 kg female), which is an approximation only. For short stature, follow institutional guidance; some references use alternative equations or a small per-inch subtraction below 60 in. This calculator flags results at or below 60 in.
- Is this IBW calculator free and mobile-friendly?
- Yes. It is completely free, needs no account, and runs entirely in your browser, so it works on a phone. It is a study and practice aid only — weight-based dosing requires an independent double-check against the order, the drug reference, and institutional policy before administering.
Put the number to work
From weight to a safe dose
IBW and adjusted body weight are inputs to weight-based dosing. Use the full dosage calculator to turn a weight into a dose, work body surface area for BSA-dosed drugs, or explore the other free calculators.
This calculator and all study material on this site are provided for practice and study only — they are not medical advice or a substitute for clinical judgment, a drug reference, or institutional policy. IBW is a dosing reference, not a weight-loss goal. Verify every dose before administering. NCLEX® is a registered trademark of the National Council of State Boards of Nursing, Inc. (NCSBN), which does not endorse or sponsor this site.