IBW / Predicted Body Weight
Height and sex — not actual weight — set lung-protective tidal volumes. Calculate PBW and the full 4–8 mL/kg table.
Written by Apex Respiratory Editorial Team
Enter a height to calculate predicted body weight.
Why predicted weight, not actual weight
Lung volume scales with height and sex, not body mass. Setting tidal volume from actual weight in a larger patient over-distends normal-sized lungs — the injury pattern the ARDSnet trial showed kills. The 6 mL/kg PBW start (range 4–8) cut mortality by ~9 absolute percentage points versus 12 mL/kg.
Inches use the Devine form (2.3 kg/in over 60 in); centimeters use the ARDSnet metric form (0.91 kg/cm over 152.4 cm). The two differ by well under 1% across adult heights.
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Sources
- Acute Respiratory Distress Syndrome Network; Brower RG, Matthay MA, Morris A, et al. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. 2000;342(18):1301-1308.
- Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650-655.
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021.