Accurately calculate PBW, IBW, and Adjusted Body Weight using clinical formulas.
Male
Female
Required for the Devine formula calculation.
Feet
Inches
Please enter a valid height.
Used to calculate Adjusted Body Weight (AjBW).
Please enter a positive weight value.
Predicted Body Weight (PBW)
166.4 lbs
Based on Devine Formula
Ideal Body Weight (IBW)
166.4 lbs
Adjusted Body Weight
175.8 lbs
Height in Cm
177.8 cm
Calculation Breakdown
Metric
Value (lbs)
Value (kg)
Description
Weight Metrics Comparison
Visual comparison of Actual vs. Predicted vs. Adjusted weights.
What is a Predicted Body Weight Calculator?
A predicted body weight calculator is a specialized clinical tool used to estimate the appropriate weight for an individual based on their height and biological sex, rather than their actual adipose tissue or muscle mass. Unlike a standard scale that tells you what you currently weigh, the predicted body weight calculator determines what a person of your stature implies physiologically.
This metric is critical in medical settings, particularly for calculating ventilator tidal volumes (ARDSnet protocol) and dosing certain medications with narrow therapeutic indices. While closely related to "Ideal Body Weight" (IBW), the term Predicted Body Weight (PBW) is specifically favored in critical care medicine to avoid the aesthetic connotations of "ideal."
Using a precise predicted body weight calculator helps clinicians and dietitians make safer decisions regarding mechanical ventilation and nutritional support, ensuring that interventions are scaled to the size of the lungs and metabolic needs rather than total body mass, which may be skewed by obesity.
Predicted Body Weight Calculator Formula and Mathematical Explanation
The core mathematics behind our predicted body weight calculator typically relies on the Devine Formula (1974), which is the industry standard for most medical applications.
The formula assumes a baseline weight for a height of 5 feet (60 inches) and adds a specific amount of weight for every inch over 5 feet.
Scenario: A male patient stands 5 feet 10 inches tall (70 inches). He is admitted to the ICU and requires mechanical ventilation. His actual weight is 220 lbs (obese).
Interpretation: The predicted body weight calculator result of 73 kg is used to set the tidal volume (usually 6-8 mL/kg of PBW). If the actual weight of 100 kg (220 lbs) were used, the tidal volume would be dangerously high, potentially causing lung injury.
Example 2: Nutritional Dosing (Adjusted Body Weight)
Scenario: A female patient is 5 feet 4 inches (64 inches) tall and weighs 180 lbs (81.8 kg). A dietitian needs to calculate her energy requirements.
Calculation: PBW/IBW = 45.5 + (2.3 × 4) = 45.5 + 9.2 = 54.7 kg (120 lbs).
Since her actual weight is >130% of IBW, the dietitian uses Adjusted Body Weight.
AjBW = IBW + 0.4 × (Actual – IBW) = 54.7 + 0.4 × (81.8 – 54.7) = 65.5 kg.
How to Use This Predicted Body Weight Calculator
Select Biological Sex: Choose Male or Female. This changes the baseline constant in the formula (50 vs 45.5).
Enter Height: Input your height in feet and inches. This is the most sensitive variable in the predicted body weight calculator.
Enter Actual Weight: Input your current scale weight. This is required to calculate the "Adjusted Body Weight," which is useful when actual weight differs significantly from predicted weight.
Review Results:
PBW: Your medically predicted weight.
IBW: Synonymous with PBW in this tool (Devine formula).
AjBW: A corrected weight used for nutritional calculations in overweight individuals.
Key Factors That Affect Predicted Body Weight Results
When using a predicted body weight calculator, several factors influence the clinical application of the result:
Height Accuracy: Since the formula multiplies every inch above 5ft by 2.3kg, a 2-inch error can skew the result by ~4.6kg (10lbs). Accurate measurement is vital.
Biological Sex: Men generally have higher muscle mass and bone density, justifying the higher baseline of 50kg compared to 45.5kg for women.
Amputations: The standard predicted body weight calculator does not account for limb loss. Clinical adjustments (e.g., subtracting 5-6% for a below-knee amputation) must be made manually.
Frame Size: The Devine formula assumes a medium frame. It does not adjust for small or large skeletal frames, which is a known limitation.
Age Factors: PBW formulas are designed for adults. They are not applicable to pediatrics where growth charts are the standard.
Clinical Context: In renal failure or fluid overload (edema), actual weight is misleading. PBW provides a stable "dry weight" benchmark for dialysis dosing.
Frequently Asked Questions (FAQ)
Is Predicted Body Weight the same as Ideal Body Weight?
Mathematically, they often use the same formula (Devine). However, "Predicted Body Weight" is the preferred term in critical care and respiratory therapy to emphasize its use for physiological prediction rather than an aesthetic "ideal."
Why does the predicted body weight calculator not ask for age?
Once adulthood is reached, height-based weight prediction remains constant. Metabolic rates change with age, but the structural predicted weight based on skeletal height does not.
Can I use this for weight loss goals?
While you can use the result as a general reference, this calculator is designed for medical safety (drug dosing/ventilation). For weight loss, a BMI or Body Composition analysis is often more appropriate.
What if I am under 5 feet tall?
The standard Devine formula subtracts weight for height under 5 feet, but accuracy diminishes. Clinical judgment is often required for very short stature adults.
How is Adjusted Body Weight different?
Adjusted Body Weight is used when a person is significantly overweight (usually >120-130% of IBW). It accounts for the fact that adipose tissue is less metabolically active than lean tissue.
Is this accurate for bodybuilders?
No. Predicted body weight calculators do not account for high muscle mass. A bodybuilder may be "overweight" by this metric but have low body fat.
Does this calculator use the Robinson formula?
This tool uses the Devine formula, which is the most widely accepted. The Robinson, Miller, and Hamwi formulas produce slightly different results but follow similar logic.
Why is PBW important for ventilators?
Lungs do not grow larger as you gain fat. Setting ventilator volumes based on actual obese weight can over-inflate and damage the lungs. PBW ensures volumes match lung size.