The Broca formula was developed in 1871 by Pierre Paul Broca (a French Army Doctor) to help establish ideal body weight. The formula (Broca Index or BI) formed the benchmark for other calculations that we know today. Initially, the BI was used to work out the normal weight but was later expanded to Ideal Body Weight.

Normal Body Weight (kg) = [Height (cm) - 100]

The Broca formula has different calculations for men and women:

Men: Ideal Body Weight (kg) = [Height (cm) - 100] - ([Height (cm) - 100] x 10%)

Women: Ideal Body Weight (kg) = [Height (cm) - 100] + ([Height (cm) - 100] x 15%)

This formulae is considered out-dated and medical practitioners prefer to use BMI that utilizes weight and height.

Measuring instruments

You only require a stadiometer to get the correct height.

The Procedure

To get the normal body weight using BI, only height is required in centimetres. Then, less 100 from the height. To get the Ideal Body Weight, you calculate and subtract 10% of the normal weight.

Example: what is the ideal weight for a man weighing 175 centimetres?

Height = 185 cm

Normal weight = 185 - 100 = 85 kilograms

Ideal body weight = 85kg - 10% = 76.5 kilograms

The target population

While the Broca Index is not applied because later methods of getting the right weight have been adopted, it is still a good method for people in the middle ages and with average body sizes to estimate their ideal body weights.

Pros of using BI

Cons of using BI

Additional Comments

While BI was a great stride in history, life was rather simplistic, and issues such as obesity were uncommon. However, the changing lifestyle patterns have thrown into the spin myriads of factors that determine the body weight. Therefore, this formula should not be applied in the current setting. It is better to use alternative measurements such as BMI.