How To Measure For Interior Doors

How To Measure For Interior Doors: A Comprehensive Guide

Accurate measurement is paramount when replacing or installing interior doors. Incorrect measurements can lead to doors that don't fit properly, causing operational issues, aesthetic flaws, and increased installation costs. This article provides a detailed guide on how to measure for interior doors, ensuring a precise fit and a smooth installation process.

Prior to beginning the measuring process, gather the necessary tools. These commonly include:

Measuring tape (preferably a steel tape measure for accuracy)

Pencil and paper for recording measurements

Level

Straight edge (optional, but helpful for verifying squareness)

It is crucial to take multiple measurements at different points and note the smallest dimension. Door frames are rarely perfectly square or even, and relying on a single measurement can lead to problems.

Measuring the Door Opening: Height

Measuring the height of the door opening involves determining the vertical distance from the finished floor to the top of the door frame. It is essential to measure from the finished floor, meaning the actual surface upon which the door will swing (e.g., tile, hardwood, carpet). If the flooring is not yet installed, account for the anticipated flooring thickness when taking this measurement.

Take height measurements at three points: the left jamb, the center, and the right jamb. The jamb is the vertical component of the door frame. Position the measuring tape vertically against each jamb and note the distance to the header, which is the horizontal component at the top of the frame. Record all three measurements. Use the smallest of the three measurements as the accurate height of the door opening. This allows for slight variations in the frame’s construction or settling over time.

For example, if the measurements are 80 inches on the left, 79 7/8 inches in the center, and 80 1/8 inches on the right, the correct door height to order should be 79 7/8 inches. This ensures the door will fit without binding against the top of the frame.

If the existing door is being replaced, measuring the height of the old door can provide a useful reference point. However, do not solely rely on this measurement, as the frame itself may have shifted or changed over time. Always measure the opening itself.

In cases where a new frame is also being installed, ensure the frame is plumb and level before taking height measurements. An un-level frame will skew the measurements and result in an improperly sized door.

Measuring the Door Opening: Width

Measuring the width of the door opening involves determining the horizontal distance between the left and right jambs. Similar to height measurements, it is crucial to take multiple measurements at different points to account for any irregularities in the frame.

Take width measurements at three points: the top, the middle, and the bottom of the opening. Position the measuring tape horizontally and measure the distance between the inside edges of the jambs at each of these points. Record all three measurements. Use the smallest of the three measurements as the accurate width of the door opening. This approach addresses any potential bowing or twisting of the jambs.

For example, if the measurements are 30 inches at the top, 29 7/8 inches in the middle, and 30 1/4 inches at the bottom, the correct door width to order should be 29 7/8 inches. This guarantees that the door will fit without being too wide to close properly.

When measuring for double doors, measure the width of the entire opening, then divide by two to determine the width of each individual door. However, remember to account for the space needed for the astragal, which is the vertical molding that seals the gap between the two doors. The astragal's width needs to be subtracted from the overall width before dividing by two.

Again, if replacing an existing door, measuring the old door’s width can be helpful for comparison, but it is not a substitute for measuring the actual opening. Frame integrity is critical, and measuring the opening directly addresses the frame's current dimensions, not its original dimensions.

If a new frame is being installed, ensure the jambs are parallel to each other before taking width measurements. Non-parallel jambs will cause the door to bind when opening or closing.

Measuring the Door Opening: Thickness and Jamb Depth

While height and width are the primary measurements for door size, understanding the jamb thickness and depth is critical for proper installation and functionality. Jamb thickness refers to the thickness of the wood used to construct the door frame, and jamb depth refers to the distance from the outside edge of the jamb to the inside edge where the door sits when closed.

To measure jamb thickness, use a measuring tape or calipers to determine the thickness of the wood used to create the jamb. This measurement is typically standardized (e.g., 1 inch, 1 1/4 inches), but it's crucial to verify the actual thickness of the existing frame.

To measure jamb depth, measure from the outside edge of the jamb (the part that butts against the wall) to the inside edge where the door closes. This measurement is vital to ensure the door casing will properly cover the gap between the frame and the wall. Standard jamb depths often correspond to standard wall thicknesses (e.g., 4 1/2 inches for a 2x4 wall with 1/2 inch drywall on each side). However, older homes or homes with non-standard wall construction may have different jamb depths.

If replacing an existing door and frame, the new jamb depth should match the existing jamb depth to avoid having to modify the wall or casing. If installing a new door in an existing frame, verify that the door's thickness is compatible with the frame's jamb depth. A door that is too thick may not close properly, while a door that is too thin may leave a large gap between the door and the frame.

In situations where the jamb depth is insufficient, extension jambs can be used to increase the depth. These are strips of wood that are attached to the existing jambs to make them wider.

When ordering a pre-hung door (a door already mounted in a frame), the jamb depth is usually specified, so accurate measurement is essential to ensure a proper fit.

Ignoring jamb depth can lead to problems during installation, such as the door casing not sitting flush against the wall or the door not closing properly. Therefore, take the time to accurately measure the jamb thickness and depth to avoid these issues.

After capturing the measurements, confirm if the existing door frame is square. Use a level to ensure both jambs are plumb, and the header is level. If the frame is out of square, note the extent of the deviation as this will affect the installation process. Significant out-of-square conditions may require shimming or other adjustments to ensure the new door operates correctly.

Document all measurements carefully. Create a clear diagram including all recorded values for height, width, and jamb dimensions. This documentation serves as a reference during the door selection and installation phases.

By adhering to these guidelines, it is possible to measure accurately for interior doors, leading to a successful installation and door operation.