Many state and local codes consider a building's wall-to-window ratio in determining its energy efficiency. Building codes vary between jurisdictions. You may have to calculate a building's wall-to-window ratio to ascertain what additional insulation is required to meet your local building code. You can determine this ratio by taking some basic measurements yourself, without the assistance of a professional.

## Step 1

Measure the length and width of each exterior wall of the building. Multiply the length times width to get the total area of each wall. Keep a record of these numbers.

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## Step 2

Measure the length and width for each rough window opening on the wall. Multiply the length times width of each window opening. Keep a record of these numbers.

## Step 3

Add the total areas of every exterior wall together. This number is the total of the exterior wall space of the building.

## Step 4

Add up all the window openings in the building. This is the total window space in the building.

## Step 5

Divide the number of the total exterior wall area by the total area of all the window openings in the building. This is the wall-to-window ratio of the building.