anesthesia.ai
All calculators

Drug-specific dosing weight

The body-weight calculator gives four scalars and leaves the choice open. This one looks up the basis a named source states for one drug, and shows the kilograms that basis gives. Where two sources name different bases, both are shown, because the calculator does not choose.

Sex
years

The calculator reads the adult statements from 18 years.

cm
kg

The list follows drug class order. This drug is in the neuromuscular blocker class.

Enter an age, a height and an actual body weight. Then choose a drug to see the weight basis its source states.

Class-level statements

Read these statements. The calculator does not apply them to any drug automatically, because a drug can contradict its own class.

  • Most anesthetic drugs

    With the exception of neuromuscular antagonists, lean body weight is the optimal dosing scalar for most drugs used in anaesthesia, including opioids and induction agents.

    Ingrande & Lemmens, Br J Anaesth 2010;105(Suppl 1):i16-i23

  • Non-depolarising neuromuscular blockers

    Dosing is often based on ideal body weight to prevent prolonged paralysis, because the volume of distribution of these hydrophilic drugs stays relatively consistent.

    OpenAnesthesia, neuromuscular blockade; WFSA Anaesthesia Tutorial of the Week, perioperative care for bariatric surgery

  • Intraoperative opioids

    Dose using lean body weight to begin with, then titrate to effect once the patient is awake.

    WFSA Anaesthesia Tutorial of the Week, perioperative care for bariatric surgery

  • Local anesthetic maximum doses

    Calculate maximum doses according to ideal body weight.

    WFSA Update in Anaesthesia vol 34, morbid obesity in pregnancy

  • General bariatric rule

    Base drug dosing on ideal body weight or adjusted body weight to avoid overdosing, with suxamethonium named as the exception.

    WFSA Anaesthesia Tutorial of the Week, perioperative care for bariatric surgery

What this table assumes

  • Every source in this table is describing obesity. Near a normal body mass index the four scalars sit close together and the choice moves the number very little.
  • Where two sources name different scalars for one drug, both are returned with the source that states each. This calculator does not choose between them.
  • A drug the sources do not name is refused rather than dosed from its class, because a drug can contradict its own class.
  • The output is a weight in kilograms and the basis that produced it. Milligrams per kilogram belong to the label and to the guideline.

This calculator looks up what a named source states for one drug. It does not resolve a disagreement between two sources, it does not apply a class statement to a drug the sources do not name, and it does not print a dose.

Formula

  • Total (actual) body weight is the measured weight; the sources use actual and total for the same quantity
  • IBW (kg): male 50 + 2.3 x (inches over 60); female 45.5 + 2.3 x (inches over 60)
  • AdjBW (kg) = IBW + 0.4 x (actual weight - IBW)
  • LBW (kg): male 9270 x TBW / (6680 + 216 x BMI); female 9270 x TBW / (8780 + 244 x BMI)
  • The basis for each drug is looked up from a named source, not derived

Source

  • Devine 1974 (ideal body weight) and Janmahasatian 2005 (lean body weight) for the scalars. Drug-specific bases per statement: FDA labels via DailyMed (rocuronium, remifentanil ULTIVA, midazolam, sugammadex BRIDION); WFSA Anaesthesia Tutorial of the Week (perioperative care for bariatric surgery; propofol infusion syndrome; paediatric TIVA; dexmedetomidine ATOTW 469; overview of sugammadex); WFSA Update in Anaesthesia vol 21 (obesity in anaesthesia) and vol 34 (morbid obesity in pregnancy); OpenAnesthesia (bariatric surgery, succinylcholine, neuromuscular blockade, cardiopulmonary bypass anticoagulation); ASRA News (transversus thoracic plane block; ketamine infusion on regular wards); StatPearls NBK539881 (lidocaine); ACC/AHA guideline (J Am Coll Cardiol 2025); ASHP/IDSA/SIS/SHEA 2013 Clinical Practice Guidelines for Antimicrobial Prophylaxis in Surgery (Bratzler et al.); Ingrande & Lemmens, Br J Anaesth 2010;105(Suppl 1):i16-i23.

Clinical reference only. Verify independently; clinical judgment governs.