Compare your weight with a historical height-based reference.
Broca reference weight
—Enter your measurements
Your weight in context
90–110% of reference · comparison convention
Compare reference formulas
Different equations, different reference estimates.
A separate screening measure.
Text summary · PDF in member tools
Step-by-step calculation
How this estimate is calculated
The original Broca rule is height (cm) − 100.
This page defaults to the sex-adjusted variant.
Frequently asked questions
What is the Broca index?
Here it is your current weight divided by the selected Broca reference weight, multiplied by 100. A value of 100% means the two weights match. The term has different historical uses, so the equation and variant are shown explicitly.
Why do the formulas disagree?
These equations use different constants and were developed for different purposes and populations. Devine, Robinson and Miller estimates are shown for comparison, not as competing diagnoses or personalized weight-loss targets. This page uses the coefficients tabulated by Peterson et al. (2016).
Is this a healthy weight target?
A Broca result alone cannot determine a healthy or appropriate target for you. It does not measure body fat, muscle, frame size or clinical condition. The 90–110% band is a display convention relative to the selected formula, not a validated clinical risk range.
What is original vs. modified Broca?
The original height-minus-100 rule gives a reference weight in kg from height in cm. This page defaults to a sex-adjusted modified convention: multiply the original result by 0.90 for men or 0.85 for women. The historical original rule is not itself sex-adjusted.
Who can use this comparison?
This page is an educational comparison for adults, not a pediatric, pregnancy, eating-disorder or medication-dosing tool. The supported input range is 120–250 cm and 25–350 kg. Devine, Robinson and Miller are not extrapolated below 152.4 cm; BMI is displayed numerically without assigning a health category.
What does the Broca Index calculate?
It compares your current adult weight with a height-based original or modified Broca reference. You enter biological sex, height and current weight, and the reference weight is calculated automatically.
Which values should I enter?
Enter height and current weight in the selected units, choose a biological-sex equation and select original or modified Broca. You do not need to supply an ideal weight.
What formula does this calculator use?
Original Broca is height in cm minus 100. Modified Broca multiplies that result by 0.90 for men or 0.85 for women. Index = current weight / selected reference × 100; difference = current weight − reference.
Why might my result differ from another source?
Check whether original or modified Broca is selected, the sex coefficient and the input units. This page preserves full precision internally and rounds the displayed values. Other reference formulas are different models.
Does the result update automatically?
Yes. Changing height, weight, sex or equation variant recalculates the result, ruler and comparison chart. Unit switches preserve the underlying measurements. Invalid entries clear all previous calculated results.
Sources & references
References inform the content; no institutional endorsement.
