Pick from:
[a]. Be sure to measure from the surface of the jambs or frame, not from the short extensions that hold the window in place. A slide rule with extension may result in more accurate interior measurements.;
[b]. If you want to use a zip-locked sliding window, you can remove the top half of the roll and insert a straight edge through the center of each roll. If you don't want to take the roll off the top, use a ruler or tape measure to get the measurements.;
[c]. If you need an 8 inch window opening for each room in your house, use the same measurement as with the width. If you want to measure for every square foot of your house, such as the width of your front porch, then the distance from the top of the front porch to the bottom is 1 foot.;
[d]. Draw a straight line along the length of your window, leaving a noticeable " clue " of measurements around that length. If your windows/windows/windows/windows/building use came with instructions, follow those directions.;Choose from options above and answer: What most naturally follows?

How to measure your windows 
Measure the width at three points and use the smallest measurement. 
Use a tape measure or extendable slide rule to measure the width of the window opening at the base, middle, and top. Write down the smallest of these measurements as the width.
Answer:
[a].