An older home’s window openings rarely fit today’s standard sizes. Measuring your window openings for replacement windows is not difficult, but it is imperative that it is done correctly. Although there are many companies that will deliver your windows, custom orders are not usually returnable or refundable due to incorrect measurements.

Consider buying a new quality tape measure. Sound silly? Remember one tool is used in this crucial step of your investment, so make sure it’s accurate. Older tapes can easily have 1/8" to 1/4" play in the tongue and have obscured increments on the tape, making it hard to read and potentially record a bad result. A house of new windows can easily cost $8,000.00 and up. A new quality tape that can be used for many more projects afterwards may run $25.00. Many professional home builders and remodeling contractors realize the huge cost of inaccurate measurements and purchase new tape measures for every project.

Start with a clean pad of paper. On a full sheet draw your home’s floor plan with window openings called out by using a number or letter referencing each specific window. This step will eliminate confusion not only during the measuring process, but with installation process as well. Remember the delivery truck will come full of windows in no specific order. Do not try to write the window dimensions on the floor plan page as there is never enough space for all the necessary information.

Pick your first window and raise the bottom sash. Measure the width at the bottom of the window opening from jamb to jamb. Do not measure from the inside stops (parting bead), but rather the opening where the window sash rests when closed. Now close the window and measure at the middle then top. Write each measurement down on a second piece of paper. This second piece of paper will be your scratch paper. Determine the smallest of the three measurements and subtract a 1/4". This 1/4" will give you 1/8" on either side for "wiggle room" during the installation and if the window opening is out of square, the room needed to adjust for level. Circle the measurement for added visibility.

The process is repeated for determining the height by measuring from where the current window sash rests (window well) when closed to the upper window jamb. Do not measure from the top of the stool (window sill). It may help to remember that the replacement window will rest in the window well, not on top of the sill. Again, determine the smallest measurement and now subtract 1/2". Most quality replacement windows are approximately 4" in width. The 1/2" will allow the new window to be placed on an angle and pushed upright in the opening also allowing space for the window unit to be leveled.

On a third sheet of paper, write down the circled measurements next to the room and the corresponding letter or number. This is your master copy, so keep it neat and easy to read.

An example might be: LIVING ROOM (A) 35 ¼" X 68 ¾"

(B) 35 ½" X 69"

(C) 35 ¼" X 68 ½"

If there is any doubt, go back and re-measure. Give yourself wiggle room for your installation. It is no fun chiseling out space for a window that is too big for an opening. With that said, a window that is too small will lose R value due to large gaps. This defeats the purpose of installing energy efficient replacement windows to begin with.