# Calculating Body Composition¶

This is a collection of the most popular bodyfat percentage equations calculated by measuring various skinfold sites in millimeters.

Here is the typical workflow for calculating bodyfat percentage from skinfold sites:

1. Collect the measurements from the skinfold sites required by the equation you chose. Appropriate skinfold sites can be found in the documentation.
2. Calculate body density.
3. Calculate bodyfat using the above body density value.

Every subclass in this module inherits from the GenericCalculator class which has 5 methods that calculate bodyfat percentage from body density:

• brozek()
• ortiz()
• schutte()
• siri()
• wagner()

These methods are required to convert body density to bodyfat in all but one equation.

If you’re unsure which calculation to use, chose siri() because it is generically applicable to most populations.

Here is a hypothetical example.

A 40 year old female whose skinfold measurements in millimeters are:

• triceps = 7
• biceps = 5
• subscapular = 4
• suprailliac = 10

To instantiate classes in this module pass the following arguments in this order:

• Age
• Sex
• A list of skinfold measurements. Order does not matter.
```>>> from fitness_tools.composition.bodyfat import DurninWomersley
>>> calc = DurninWomersley(40, 'female', (7, 5, 4, 10))
>>> calc.body_density()

# body density value

1.046703631104186

# pass the body density value to a bodyfat equation inherited from GenericCalculator

>>> calc.siri(calc.body_density())
22.9
```

According to the Durnin Womersley equation our hypothetical female’s bodyfat is 22.9%.

As noted above, there is one equation that converts your measurements directly into bodyfat. This is the JacksonPollock4Site class.

Lets do another run through.

A 25 year old male skinfold measurements in millimeters are:

• abdominal = 6
• triceps = 6
• thigh = 8
• suprailiac = 6
```>>> from fitness_tools.composition.bodyfat import JacksonPollock4Site
>>> calc = JacksonPollock4Site(25, 'male', (6, 5, 8, 6))

# Calculates bodyfat directly

>>> calc.body_fat()
5.2
```

Our hypothetical male has a bodyfat percent of 5.2%.