Getting the right measurements is key, whether you need to replace a damaged window or if it's simply time to upgrade your windows to maintain your home's financial value and security. But where to start? In this guide, we go over everything you need to know about measuring for replacement windows, including the parts of the window you need to measure and measurement considerations for certain types of windows. Keep reading to learn how to measure windows for replacement.

Parts Of a Window to Measure

Before you learn how to measure windows for replacement, it's important to familiarize yourself with the parts of the window you'll need to measure. Below, we've outlined them for you.

Window Jambs: The window jambs are located on either side of the window frame and stretch the length of the window frame on both sides. The window jambs are part of the walls of your home and don't come with replacement windows. They typically have specific designs that help hold the sash portion of the window in place and make it easier to open the window. Most window jambs can accommodate a range of window types. If needed, you can purchase a jamb extender or a window with an adjustable sash to ensure the right fit.

Sash: The window sash refers to the frame portion of the window that surrounds the entire window pane on all sides and keeps the window pane in place. The sash portion of the window rests snugly against the window jambs and the head and sill portions of the window frame. Some windows also have a sash that runs along the middle (also called the rail) of the window separating two or more panes of glass (common for double-hung windows). Some window sashes are also adjustable to help windows fit better inside the frame!

Sill: The sill portion of the window is the bottom part of the window frame on which the lower sash rests. The window sill sometimes has a decorative element or a ledge for decorations.

Head: The head of the window is the top portion of the window frame connected to the wall that rests against the upper sash.

How to Measure Windows for Replacement

Measuring for replacement windows is much easier than you might think! Follow these steps to learn how to measure windows to find the right replacement size.

Skill-Level:

Beginner

Number of People:

1–2 people (to help hold the tape measure)

Time Requirements:

30 minutes or less per window

What You Will Need:

• Notepad
• Pencil
• Tape measure
• Ladder (optional depending on the height/location of the window)
• Level

1. Check Your Window's Alignment

Believe it or not, your current window might not be perfectly aligned within the window frame, and this can affect the accuracy of your measurements. So the first step is making sure your current window fits right in your window frame. To do this, you will need to check if your window is square, level, and plumb.

For Squareness:

Before you learn how to measure replacement windows, you need to determine if your current window fits squarely in the frame. Start by measuring from the top left corner (where the side and upper sash touch the head) to the bottom right corner (where the side and bottom sash meets the sill) and then from the top right corner to the bottom left corner. If both of these measurements are around the same (no more than ¼" difference), you know your window is sitting in the frame evenly. If not, this might mean that the frame itself is uneven. You can easily remedy this by looking for a replacement window with an adjustable sash to help the window fit snug and level in the frame, or by making adjustments to the window jamb portion of the frame.

For Levelness:

Similarly, you also need to check if your window is properly level (horizontally straight), as this can impact the accuracy of your height measurements. Place a level on the window sill and check if the bubbles are in the center. If they are, this means your window/frame is properly level. If you have double-hung windows, you'll also want to place a level on the center rail sash to make sure the bottom pane is level.

For Plumb:

You also need to make sure your windows are plumb (vertically straight), as this can impact the accuracy of your width measurements. To do this, place the level beside the face of the window jam (the portion of the window frame that juts out next to the side sash portions). If the bubbles are in the center, you know your window is plumb, Repeat this process on the opposite side of the window just to be sure. If the window isn't plumb, you may need to reset it in the frame.

2. Measure the Width

Once you’ve checked the window’s alignment, it’s time to start measuring for its replacement. To start, take your tape measure and measure the width of your current window starting from the part of the side sash that touches the window jamb to the sash/window jamb portion on the other side. We recommend measuring the width at the center of the window first and then comparing this measurement to additional width measurements taken at the lower and upper portions of the window. This is important because not all windows are perfectly square, as we discussed in step one (especially if you have an older home with lots of character). Once you are certain of the width of your window, take ⅛" to ¼" off of your measurements (to ensure the window can slide into place) and record it on a piece of paper before moving on to measuring the window’s height.

3. Measure the Height

Take your tape measure and begin your measurements at the point where the lower sash meets the window sill. You might need an extra pair of hands to hold the start of the tape measure in place as you measure upwards. Measure to where the upper sash meets the head portion of the window frame. Take ⅛" to ¼" off the total height measurement to make it easier to fit the window within the frame. Double-check your measurements and record the height for future reference. Depending on the height of your windows, you may also need a step stool or ladder to complete this measurement!

Tip!

When learning how to measure windows for replacement, always go with the smallest measurement. This way you can always adjust the sash within the frame to accommodate the window size.

4. Measure the Window Jamb Depth

For this step, you'll need to open your window to access the full window jamb. Measure the width of your window jamb from edge to edge and repeat the process on the other side of the window. Standard window jambs are usually around 3" wide and accommodate most window sashes. The reason to take this window jamb measurement is because you don’t want the window to jut out of the frame, especially if it is super narrow.

5. Consider the Window's Opening Orientation

Vertical and horizontal sliding windows don't require additional measurements (standard window height and width measurements will do!). However, if you have awning, casement, hopper, or pivot windows, you'll want to measure how wide the window opens. To do this, open the window as far as it can go (whether it opens inwards, outwards, or pivots). Measure starting from the middle edge of the window, across the opening to the edge of the window frame. Record this measurement. Then do the same thing but measure the distance between the edge of the open window pane and surrounding objects (walls, cabinets, furniture) to determine the maximum opening orientation you can afford.

Tip!

Search "Window" in the "Search This Category" tab to the bottom left-hand side of the product page for window locks, opening mechanisms, and accessories.

6. Consider Measuring for Window Screens

Some windows come with window screens that match the size of the window pane, but you can also source them yourself. Most window screens have their own sash that fits snugly against the outer portion of the window jambs, against the window sill, and against the bottom edge of the middle rail sash. Measure from the edge of the screen that touches the window jamb to the other side. Then measure starting from the bottom portion of the screen that meets the window sill to the top portion of the frame that meets the center rail or the head of the window frame. Subtract about ⅛" from your total measurements for a good fit.

Tip!

Check out our guide on How to Measure Windows for Blinds to promote privacy and help filter sunlight.

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