Enter the total open area of a louver and the overall wall opening area into the calculator to determine the louver free area.

Louver Free Area Formula

The following equation is used to calculate the Free Area.

LFR = TOLA / WOA *100
  • Where LFR is the louver free area (%)
  • TOLA is the total open area of the louver after subtracting obstructions, blades, and frames (ft^2)
  • WOA is the wall opening area (ft^2)

To calculate louver free area, divide the total open area of the louver by the wall opening area, then multiply by 100.

What is Louver Free Area?


The free area of a louver is the clear space that exists between louvers when full open. The free area can be used as an air passage for fresh air and daylighting. In some cases, it is used as a component to control solar gain.

The larger the free area, the greater the energy savings potential. The greater the air passage area, the more cooling and ventilation capacity available.

In general, there are two categories of louvers: solid plastic blades and mesh blades. Solid plastic blade louvers are excellent for use as sun protection or solar control. Solid plastic blades do not allow light passage through them.

Mesh blade louvers provide a combination of light diffusion, solar protection and ventilation control (the same function as solid plastic blade louvers). Mesh blades are made from wire or screen material (metal and/or fabric).

Free Area: The free area is measured by opening the louver to its maximum opening position both vertically and horizontally. The measurement is taken from one edge of the horizontal louvers to another edge of the vertical louvers at their widest point (halfway between each row). The measurement does not include any portion of the blade support structure.

How to Calculate Louver Free Area?

Example Problem:

The following example outlines the steps and information needed to calculate Free Area.

First, determine the total louver area minus the obstructions, blades, and frames. For this example, this is found to be 10 ft^2.

Next, determine the total wall opening area. In this case, the wall opening as an area of 20ft^2.

Finally, calculate the louver free area using the formula above:

LFR = TOLA / WOA *100

LFR = 10 / 20 *100

LFR = 50%