Key Takeaways
- Knowing how to measure for a new construction window starts with learning how to measure a rough opening for a window.
- The rough opening measurements should match the rough opening requirements of the window you choose.
- Measure between the studs at the top, middle and bottom and use the smallest measurement as the rough opening width.
- Measure from the header to the rough sill at the left, middle and right and use the smallest measurement as the rough opening height.
- Use a level to ensure the rough opening is level and plumb.
- Measure from the bottom corners diagonally to the top corners to ensure the measurements are the same and the opening is square.
- Measure from the sheathing to the inside of the wall framing and add the drywall thickness — usually 1/2 inch — to determine the rough opening depth.
What Is a New Construction Window?
A new construction window is designed for installation during construction of a new home or a new home addition rather than as a replacement for an existing window. Unlike a replacement window, a new construction window has a nailing flange on each side to secure the new window to the exterior sheathing.
The steps below outline how to measure for new construction windows for a new home. If you’re replacing existing windows, see our tips on measuring for replacement windows.
Key Terms for New Construction Window Measurement
- Rough Opening (RO): The framed opening for a window
- Header: The horizontal frame element at the top of the opening
- Jack Studs: The vertical frame elements on each side of the opening.
- Rough Sill: The horizontal frame element at the bottom of the opening
- Sheathing: The exterior wood sheets covering the wall frame
- Actual Size: The exact width and height of a window unit
- Common Size: The listed measurements for a window unit, typically 1/2 inch to 3/4 inch larger than the actual size.
The smaller actual size allows room for adjusting and shimming the window during installation to ensure it’s level and plumb.
Measuring for New Construction Windows
Window sizes are displayed as common sizes, typically the width first, followed by the height. Use the steps below as a general guide. Before buying windows, confirm their rough opening requirements.
Step 1: Measure the Width of the Rough Opening
- Measure at the top, middle and bottom of the rough opening.
- Measure from the face of one stud to the face of the opposite stud.
- Keep the tape measure level.
- The smallest measurement determines the window width you need.
Learn how to use and read a tape measure for accurate results.
Step 2: Measure the Height of the Rough Opening
- Measure at the far left, the middle and the far right.
- Measure from the bottom edge of the header to the face of the rough sill.
- Keep the tape measure straight.
- The smallest measurement tells you the window height you need.
Step 3: Check for Level, Plumb and Square
The rough opening needs to be within 1/16 inch to 1/8 inch of level (straight horizontally), plumb (straight vertically) and square (four 90-degree angles) for the window to fit.
- Measure diagonally from the bottom corners to the opposite top corners.
- If the measurements are equal, the rough opening is square.
- To check for level, hold a level across the rough sill and header.
- To check for plumb, hold the level against the jack studs.
Step 4: Measure Rough Opening Depth
- Measure from the exterior surface of the sheathing to the interior face of the wall framing and add the drywall thickness, typically 1/2 inch for exterior walls.
- If drywall is already in place, measure to the interior surface of the drywall.
Get tips on installation with our guide to installing a window for new construction.
Find New Construction Windows to Fit Your Home
Once you have your rough opening sizes, shop Lowes.com to find windows with rough opening measurements that match your smallest width and height measurements and that fit your rough opening depth. Or bring your measurements to your local Lowe’s. A Red Vest associate can use them to help you find windows that fit your home with the construction and features you want.