Weight Scalars

CRNA Study Suite · TBW · IBW · PBW · LBW · CBW · FFM
All Calculators Weight Scalars
Patient
Dosing Rule Reference
Dose ByDrugs
IBW / LBWRocuronium, vecuronium, cisatracurium, remifentanil, propofol induction
TBWSuccinylcholine, sugammadex, propofol maintenance, midazolam, fentanyl loading
PBWTidal volume (ARDSNet 6-8 mL/kg)
(Krogh, 2023, p. 1101; Kim et al., 2025, p. 366; Fernandez-Bustamante & Bucklin, 2024, p. 3819)
All Weight Scalars for This Patient
ScalarValue (kg)FormulaSource
Notes
IBW has three common formulations — all board-testable
• Devine (Miller's Ch 16): 50 / 45.5 + 2.3 kg/in over 60"
• Hamwi-variant (Nagelhout Ch 20): 105 / 100 lb + 6 / 5 lb/in over 5 ft
• Broca (Barash Ch 45): height (cm) − 100 M / − 105 F
Broca gives the highest value at most heights; Hamwi and Devine usually agree within 1-2 kg.
Other scalars
• PBW (Predicted Body Weight): specifically for tidal volume. Uses the ARDSNet formula.
• LBW (Lean Body Weight / Janmahasatian): more precise than IBW for drug dosing in obesity.
• CBW (Corrected / Adjusted Body Weight): IBW + 0.4 × (TBW − IBW); used for aminoglycoside dosing and some CRNA protocols.
• FFM (Fat-Free Mass): Janmahasatian formula; basis for Eleveld propofol TCI model.
References

Sheets, S. A. (2023). Preoperative evaluation and preparation of the patient. In S. Elisha, J. S. Heiner, & J. J. Nagelhout (Eds.), Nurse anesthesia (7th ed., pp. 336-375). Elsevier.

Krogh, M. A. (2023). Obesity and anesthesia practice. In S. Elisha, J. S. Heiner, & J. J. Nagelhout (Eds.), Nurse anesthesia (7th ed., pp. 1092-1108). Elsevier.

Kim, T. K., Obara, S., & Johnson, K. B. (2025). Basic principles of pharmacology. In M. A. Gropper, N. H. Cohen, L. I. Eriksson, L. A. Fleisher, S. Johnson-Akeju, & K. Leslie (Eds.), Miller's anesthesia (10th ed., pp. 347-371). Elsevier.

Fernandez-Bustamante, A., & Bucklin, B. A. (2024). Anesthesia and obesity. In B. F. Cullen, M. C. Stock, R. Ortega, C. W. Connor, & N. Nathan (Eds.), Barash, Cullen, and Stoelting's clinical anesthesia (9th ed., pp. 3814-3876). Wolters Kluwer.

How this works

The weight formulas

Ideal body weight is from height alone: IBW for men equals height in cm minus 100, IBW for women equals height in cm minus 105 (Lemmens, Brodsky, & Bernstein, 2006, p. 1082). Lean body weight is approximated as IBW multiplied by 1.3, since LBW runs roughly 20 to 40% above IBW in obese patients (Krogh, 2023, p. 1100).

Which drugs dose on which weight

As a rule, water soluble drugs are dosed by IBW and lipid soluble drugs by TBW (Krogh, 2023, p. 1100). Propofol is dosed by LBW for induction and TBW for maintenance, succinylcholine by TBW because pseudocholinesterase activity increases with body mass, the nondepolarizers (rocuronium, vecuronium, cisatracurium) by IBW, and remifentanil by IBW (Krogh, 2023, p. 1101).

References

Krogh, M. A. (2023). Obesity and anesthesia practice. In Elisha, Heiner, & Nagelhout (Eds.), Nurse anesthesia (7th ed., pp. 1092-1108). Elsevier.