Measuring the square footage of windows can be useful in custom window installations or when determining the amount of add-on materials, like solar-blocking films, that are necessary to coat the windows. You can do the job quickly with just a few simple tools and calculations.
Stretch a tape measure across the bottom of the window glass. Record the measurement in inches.
Stretch the tape from bottom to top. Record the measurement in inches.
Multiply the two numbers together. Divide the result by 144 to get the resulting square foot measurement.