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Ideal Weight Formulas and Calculation Steps

Review Devine, Robinson, Miller, Hamwi, formula average, BMI-based weight, unit conversions, variables, limits, and a worked ideal weight calculation.

How do the Ideal Weight Calculator formulas work?

This formula page defines the variables used by the Ideal Weight Calculator, shows how those values are combined, and explains the order of operations behind the result. Use the worked steps to verify an estimate, compare scenarios, and understand which assumptions or rounding rules can affect the displayed answer.

Formula Overview

The calculator runs four height-based equations. Devine, Robinson, and Miller return kilograms directly. Hamwi returns pounds before conversion. A separate BMI equation maps an entered BMI value to weight for the same height.

d=Hin−60d=H_{in}-60

The variable d is the number of inches above 5 feet. The engine accepts heights from 5 feet through its configured upper limit.

Variable Definitions

SymbolMeaningUnit
HinTotal heightinches
HmTotal heightmeters
dInches above 5 feetinches
WWeightkilograms or pounds as labeled
BUser-entered BMI valuekg/m²
WcurrentCurrent body weightkilograms

Measurement Unit Conversions

Hin=12(feet)+inchesH_{in}=12(feet)+inches
H_{cm}=H_{in} imes2.54qquad H_m= rac{H_{cm}}{100}
Wkg=Wlbimes0.45359237W_{kg}=W_{lb} imes0.45359237
W_{lb}= rac{W_{kg}}{0.45359237}

Devine Formula

Wmale=50+2.3dquadkgW_{male}=50+2.3dquad kg
Wfemale=45.5+2.3dquadkgW_{female}=45.5+2.3dquad kg

Robinson Formula

Wmale=52+1.9dquadkgW_{male}=52+1.9dquad kg
Wfemale=49+1.7dquadkgW_{female}=49+1.7dquad kg

Miller Formula

Wmale=55.7+1.39dquadkgW_{male}=55.7+1.39dquad kg
Wfemale=53.1+1.36dquadkgW_{female}=53.1+1.36dquad kg

Hamwi Formula

Wmale=106+6dquadlbW_{male}=106+6dquad lb
Wfemale=100+5dquadlbW_{female}=100+5dquad lb

The pound result is multiplied by 0.45359237 when a kilogram value is required.

Four-Formula Average and Spread

W_{average}= rac{W_D+W_R+W_M+W_H}{4}
Spread=max(WD,WR,WM,WH)−min(WD,WR,WM,WH)Spread=max(W_D,W_R,W_M,W_H)-min(W_D,W_R,W_M,W_H)

The average summarizes the four estimates. It is not a separate published ideal body weight equation. The spread shows the effect of method selection for the entered height and formula term.

BMI-Based Target and Range Formulas

Wkg=BimesHm2W_{kg}=B imes H_m^2
Wlower=BlowerHm2qquadWupper=BupperHm2W_{lower}=B_{lower}H_m^2qquad W_{upper}=B_{upper}H_m^2

The target, lower, and upper BMI values are separate user inputs. The calculator does not derive them from the four ideal body weight equations.

Current BMI and Difference

BMI_{current}= rac{W_{current}}{H_m^2}
Difference=Wcurrent−WselectedDifference=W_{current}-W_{selected}

Current weight affects only these comparison metrics. It does not change any of the four height-based estimates.

Worked Ideal Weight Calculation

An adult selects the male formula term and enters a height of 5 feet 10 inches. Therefore d equals 10.00 inches.

Devine=50+2.3(10.00)=73.000kgDevine=50+2.3(10.00)=73.000 kg
Robinson=52+1.9(10.00)=71.000kgRobinson=52+1.9(10.00)=71.000 kg
Miller=55.7+1.39(10.00)=69.600kgMiller=55.7+1.39(10.00)=69.600 kg
Hamwi=(106+6(10.00))imes0.45359237=75.296kgHamwi=(106+6(10.00)) imes0.45359237=75.296 kg
OutputEngine result
Four-formula average72.224 kg (159.23 lb)
Target-BMI weight at BMI 2269.548 kg
BMI-based range58.484 to 78.716 kg
Formula spread5.696 kg

Precision, Assumptions, and Limits

  • The engine retains precision through dependent calculations and rounds formatted displays.
  • Extra displayed digits do not make a population equation more individualized.
  • The formulas are limited to heights of at least 5 feet.
  • The male or female selection chooses the published coefficient set.
  • The BMI inputs are editable assumptions and are validated for order and range.
  • The model does not measure body composition or define a treatment target.

Ideal Weight Formula FAQ

Why do the equations disagree?

They use different base weights, per-inch increments, units, and historical purposes. The spread is expected and is one reason not to treat a single result as universal. Review the Ideal Weight Calculator formula assumptions before relying on this result for decisions.

Does the average formula have its own clinical coefficients?

No. It is the arithmetic mean of the four displayed equations. For a useful Ideal Weight Calculator formula result, enter realistic values, compare relevant scenarios, check the calculation details, and review the definitions, assumptions, and limitations before using the estimate for an important decision.

Does current weight change the ideal weight formulas?

No. It changes current BMI and the displayed difference only. For a useful Ideal Weight Calculator formula result, enter realistic values, compare relevant scenarios, check the calculation details, and review the definitions, assumptions, and limitations before using the estimate for an important decision.

References

Return to the Ideal Weight Calculator or review the step-by-step guide.

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