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Jennifer Farrington is a contributing writer at USA TODAY Homefront. She is a Florida native who has more than a decade of writing and editing experience. Jennifer has covered everything from real estate and insurance to personal finance and entertainment.
To get precise measurements for replacement windows, measure the width, height and depth.
Measure window width and height in three places, and circle the smallest measurement.
Subtract 1/2 inch from the rough width measurement and 3/8 inch from the rough height.
Whether you’ve decided to replace a window for appearance and functionality or to improve its energy efficiency, you’ll need to accurately measure the existing window before you can order a replacement unit.
To get precise measurements for your window replacement, you’ll need to measure the window’s width and height at the top, middle and bottom and determine its depth. Our step-by-step guide breaks it down.
Before you jet off to the garage in pursuit of a tape measure, know why it is so important to obtain accurate measurements when determining dimensions for replacement windows.
“Measuring windows can be tricky,” explained Larry Shapiro, co-owner of Executive Remodeling in St. Louis Park, Minnesota. “If the measurement is off by a relatively small fraction, the window won’t fit.”
Insufficient do-it-yourself (DIY) measuring may result in the window either fitting too snuggly within the opening or not fitting at all. An excessively tight fit can hinder proper operation (opening and closing the window) or result in window damage over time.
To avoid this costly disaster, you’ll want to account for an expansion gap, which is a small space left around the perimeter of the window frame. Below we get into how you can do this.
To measure windows for replacement, first, gather a piece of paper, a pencil and a tape measure. You’ll need these to record several measurements for the window’s width, height and depth. If you’re measuring multiple windows, be sure to label which measurements correspond to each window. You’ll also need a level — a tool designed to determine if a surface is horizontal or vertical.
Before measuring, check for square, plumb and level to ensure everything will align properly with your replacement window.
Square
Plumb
Level
When a window is square, it has perfect 90-degree corners. To check if your windows are square, you’ll need to do the following:
Plumb measures if your window is perfectly vertical or if it’s tilting forward or backward in the frame. You’ll need to do the following:
To check if a window is level, which measures if it’s aligned on a horizontal plane, you need to do the following:
If a window is not plumb or level, you may need to make adjustments to the opening, such as inserting wedge-shaped pieces of material called shims into gaps around the window to ensure it is vertically and horizontally level.
Measure for width horizontally from one side jamb to the other. Measure from the surface of the jambs, not the trim strips. Trim strips refer to the decorative or functional elements installed around the perimeter of your window frame.
Measure across from the top, middle and bottom and record your results. Circle the smallest measurement to use as the window width.
Tip
Homes tend to move and shift over time, which can significantly impact the shape of your window. The smallest of the three measurements usually reflects what the original window size was.
To measure the window’s height, you’ll need to measure from the top of the head jamb — excluding the trim strip — to the high point of the windowsill. Once again, measure the height three times from the left side of the window, center and right side. Record your results and circle the smallest measurement as the window’s height.
Open your window and measure from the window frame to the inside where the window frame meets the wall (i.e., the interior stop to the exterior stop). Don’t include the depth of the windowsill. Measure from the left, right and center, and circle the smallest measurement. This will be your depth.
Now that you have all three measurements, “you’ll want to take 1/4 inch off the rough width measurement and 1/4 inch off the rough height measurement,” explained Mike Gilkey, founder of Gilkey Window Company, serving Cincinnati, Chicago and Louisville, Kentucky.
This adjustment helps accommodate the expansion gap mentioned earlier, ensuring sufficient space for the new window — especially if the opening is not perfectly square — and allowing for the expansion and contraction of framing material.
Some window installation companies may advise different deductions. For instance, Gilkey confirmed, “Some suggest subtracting 1/2 an inch from the rough width measurement and 3/8 of an inch from the rough height.” Therefore, you should provide your initial measurements to a window manufacturer or installer so they can offer tailored advice on the window size you need.
Furthermore, Gilkey advises that homeowners double-check their window measurements to guarantee they comply with their city’s egress codes, which prioritize their safety.
Storm windows are more complex; they are designed differently than standard windows and contain multiple panes. To measure the width of storm windows, you’ll want to measure from side jamb to side jamb from the inside of the window. Measure at the top, middle and bottom of the window, and record the narrowest width.
To find the height, measure from the inside of the trim boards at the top of the window, or head jamb to the sill. Measure right, left and middle, and record the shortest measurement as your height.
When measuring for exterior storm windows, round down your width and height measurements to the nearest 1/8 inch. For indoor windows, round to the nearest 1/16 inch for width and height.
Before you order your windows, it’s best to consult with a storm window manufacturer for guidance.
Bay and bow windows can be measured in a few straightforward steps.
To measure the total width of the unit, place your tape measure in the middle of the unit and record the distance from side jamb to side jamb horizontally. Then, from the center, extend the tape measure from the head jamb to the sill vertically to capture the total height.
Next, measure the width of each window pane. To do this, extend your tape measure horizontally between jambs. Make sure to label each window, such as “far left panel” or “center panel,” depending on how many panels your bay window has.
To find the depth, stand between the side panels where they meet the wall, in front of the central window. Measure from this spot to the middle of the central window pane. This measurement captures how far back the bay window protrudes from the room.
Measuring for bow windows is relatively simple. First, measure the entire width from jamb to jamb. Then, record the depth from the front of the window to the middle of the window pane.
Consult a professional window installer to determine the appropriate amount of stackback allowance required. Stackback refers to the space needed for curtains and drapes to be pulled back or stacked when not in use.
As you prepare to take down the measurements for your home improvement project, remember to document both the position of the window being measured and the specific points where measurements are taken.
For example, when measuring the width of a window and obtaining measurements at the top, middle and bottom, it’s beneficial to label each dimension accordingly. Sharing these labeled measurements of your old window with a window professional will help them provide you with a correctly sized window.
As you discuss your window needs with a window installation company or major retailer, you’ll also want to discuss window style and type. You might choose to swap out a single-hung window with another single-hung window — additionally, you can choose between different framing materials such as vinyl or fiberglass and pane features including single-glaze or dual-pane frames.
Upgrading your windows from single-pane to double-pane can enhance its soundproofing capabilities.
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