Ideal Body Weight Calculator (Devine Formula)
Calculate your ideal body weight using the Devine formula — the most commonly used IBW calculation in clinical medicine for drug dosing, nutrition planning, and tidal volume estimation.
Broca Index Calculator
Calculate your ideal body weight with the Broca Index — one of the oldest and simplest height-to-weight formulas. with sex adjustments.
ft
in
Enter to compare against the ideal weight estimates
lbs
Broca Ideal Weight (Sex-Adjusted)
154.4 lbs
Height: 177.8 cm | Male
Original Broca⧉
171.5 lbs
Height − 100
Sex-Adjusted⧉
154.4 lbs
×0.90 (male)
Modified (Brugsch)⧉
149.5 lbs
Height-range adjusted
Formula Comparison
| Variant | Ideal Weight | Formula |
|---|---|---|
| Original Broca (1871) | 171.5 lbs | Height(cm) − 100 |
| Sex-Adjusted (Male) | 154.4 lbs | (Height − 100) × 0.90 |
| Modified (Brugsch) | 149.5 lbs | Height − 110 |
Deviation Guide
| Deviation | Interpretation |
|---|---|
| < −10% | Underweight |
| −10% to +10% | Normal range |
| +10% to +20% | Overweight |
| > +20% | Obese |
Disclaimer: The Broca Index is a historical estimation tool and does not replace modern clinical assessments. Consult a healthcare provider for personalized weight management advice.
Planning notes, formulas, and examples
About the Broca Index Calculator
The Broca Index is a historical ideal-body-weight formula that subtracts a fixed amount from height in centimeters. It is simple to calculate and still appears in some clinical and educational references, but it is best treated as a rough benchmark rather than a modern standard.
This page shows the original formula, common sex-adjusted variants, and a modified version so you can compare how the historical estimates differ.
When This Page Helps
The Broca Index is useful as a quick historical reference. Comparing it with newer formulas helps show how much ideal-body-weight estimates can vary.
How to Use the Inputs
- Select your preferred unit system.
- Enter your height accurately (shoes off).
- Select your sex for the adjusted calculation.
- Optionally enter your current weight to see how it compares.
- Review the original Broca value, the sex-adjusted value, and the modified Broca value.
- Compare all three estimates in the results table.
Formula used
Original Broca Index:
Ideal Weight (kg) = Height (cm) − 100
Sex-Adjusted Broca:
Male: Ideal Weight = (Height − 100) × 0.90
Female: Ideal Weight = (Height − 100) × 0.85
Modified Broca (Brugsch variant):
Height < 165 cm: Ideal = Height − 100
Height 165–175 cm: Ideal = Height − 105
Height > 175 cm: Ideal = Height − 110
Deviation = (Actual Weight − Ideal Weight) / Ideal Weight × 100%Example Calculation
Result: Original: 75.0 kg | Adjusted: 67.5 kg | Modified: 70.0 kg
A 175 cm male has an original Broca ideal weight of 175 − 100 = 75.0 kg. The sex-adjusted (male) value is 75.0 × 0.90 = 67.5 kg. The modified Brugsch variant for heights 165–175 cm gives 175 − 105 = 70.0 kg.
Tips & Best Practices
- Broca is best read as a rough reference, not a precise target.
- Comparing Broca with Devine, Robinson, Miller, and Hamwi gives a better sense of the spread between historical formulas.
- Frame size and body composition can shift how a fixed-height formula should be interpreted.
- The formula does not account for age, muscle mass, or body composition.
The History of the Broca Index
The Broca Index is one of several historical height-based ideal-weight rules. It is best understood as a simple benchmark from an earlier era of anthropometry.
Variations and Modifications
Over time, clinicians introduced sex and height adjustments to make the basic rule a little more usable, but the formula remains a rough estimate rather than a definitive standard.
Strengths and Weaknesses
Its main strength is simplicity. Its main weakness is that it does not account for frame size, body composition, or many other factors that affect weight.
Modern Context
Today the Broca Index is most useful when compared with newer formulas, not when treated as a standalone target.
Sources & Methodology
Last updated:
Methodology
This calculator applies the original Broca height-minus-100 rule and shows common sex-adjusted and height-band variants as historical reference forms. The page is intended to compare formulas, not to claim that one of them precisely defines a healthy weight.
Because Broca is a simple anthropometric rule, the result should be read as a rough estimate that can vary meaningfully from later formulas like Devine, Robinson, Miller, and Hamwi.
Sources
- Ideal body weight: A commentary (PubMed) — Discusses historical ideal-body-weight equations and their current use as reference points.
- Comparison of ideal body weight equations and published height-weight tables with body mass index tables for healthy adults in the United States (PubMed) — Compares formula-based ideal body weight estimates against published reference tables.
Frequently Asked Questions
Broca is one of the oldest height-based ideal-weight formulas and is typically cited as a historical reference rather than a current standard.
Broca is still useful as a historical comparison because of its simplicity, but newer formulas are usually preferred for practical use.
Sex-adjusted variants were introduced to make the original fixed-height rule a little closer to common clinical expectations, but they remain rough adjustments rather than validated targets.
BMI and Broca answer different questions. BMI classifies weight-for-height ranges, while Broca produces a single reference weight.
The Brugsch variant changes the amount subtracted by height band. It is a historical modification, not a universally accepted standard.
No. The formula becomes less useful at very tall or very short heights, which is one reason modern equations are often preferred.
It was designed for adults. Children should be assessed with age- and sex-specific growth references instead.
A small deviation from any historical ideal-body-weight formula is common. Broca should be interpreted as a rough reference rather than a strict threshold.
More in this topic
Healthy Weight Range Calculator
Find the adult BMI-based healthy weight range for your height in pounds, kilograms, and category context.
Ponderal Index Calculator
Calculate your Ponderal Index (PI) — mass divided by height cubed. PI is a proportionality reference used in adult and neonatal assessment.