How to Measure for an Exterior Door: A Guide

Key Takeaways:

1. Measure width, height, and depth: Get precise measurements of the door opening and frame.
2. Check for frame alignment: Ensure the door frame is level and plumb.
3. Account for rough opening: Measure the space between the studs for a pre-hung door.
4. Consider threshold height: Measure the sill height for proper installation.
5. Avoid common mistakes: Double-check measurements and account for trim and molding.

Measuring an exterior door might seem like a simple task, but it requires precision to ensure a perfect fit. Whether you’re upgrading your current door or replacing it altogether, getting the measurements right is essential for a smooth door installation. Incorrect measurements can lead to a host of problems—from drafts and energy loss to difficulties in installation and, ultimately, a less secure home.

Key points for measuring an exterior door are the following:

• Measuring Width
• Measuring Height
• Measuring Depth
• Rough Opening

This guide will walk you through the process of how to measure for an exterior door step-by-step, ensuring you have the right measurements for a perfect fit.

Why Accurate Measurements Matter

Before diving into the process, it’s important to understand why precise measurements are so critical for an exterior door. A door that doesn’t fit correctly can cause a number of issues, such as:

• Energy inefficiency: Gaps or spaces around the door can allow drafts, increasing heating and cooling costs.
• Security risks: A door that doesn’t sit properly in the frame may not close securely, making your home more vulnerable to intruders.
• Difficult installation: An ill-fitting door will require adjustments during installation, which can lead to higher labor costs or unnecessary damage to the frame.
• Aesthetic concerns: A door that’s too small or too large may detract from the overall appearance of your home’s exterior.

With these points in mind, let’s get started on how to measure your exterior door correctly.

Tools You’ll Need

Before beginning the measurement process, gather the following tools:

• Tape measure (preferably one that extends to at least 10 feet)
• Pencil and paper for recording measurements
• Level (optional, but helpful for ensuring accuracy)
• Assistant (optional, but useful for holding the tape measure)

Step-by-Step Guide on How to Measure for an Exterior Door

1. Measure the Width of the Door

The first measurement you’ll need is the width of your existing door or the door frame. To get an accurate width measurement:

• Open the door fully and measure from one side of the door frame to the other, starting at the interior trim or stop molding.
• Take measurements at three different points: the top, middle, and bottom of the door frame. Sometimes, the door frame might not be perfectly straight, and this step ensures you catch any variations.
• Record the smallest measurement of the three. This will be your door width. Standard exterior doors typically range between 30 inches and 36 inches wide.

Pro Tip: Ensure the tape measure is level to avoid inaccurate readings.

2. Measure the Height of the Door

Next, you’ll need to measure the height of your exterior door. To do this:

• Start at the top of the door frame (at the head jamb) and measure down to the bottom of the sill or threshold. Be sure to measure from the interior side of the door.
• Similar to the width, take the measurement at multiple points (left side, center, and right side) and record the smallest number. Standard door heights are usually 80 inches, but some doors may be taller, especially in custom builds.

Pro Tip: If you plan to install a pre-hung door (one that comes with a frame), you’ll also need to account for the height of the threshold or sill.

3. Measure the Depth of the Door Jamb

The door jamb depth is often overlooked but is essential for a proper fit. The jamb depth refers to the thickness of the wall that the door will sit in.

• Measure from the inside edge of the door frame to the outside edge, which is usually the thickness of the wall.
• Standard door jamb depths are typically between 4 9/16 inches and 6 9/16 inches, depending on the thickness of the walls in your home. This measurement ensures that the new door frame sits flush with the walls and trim.

Pro Tip: If your home has thicker walls or additional insulation, you may need a custom jamb depth.

4. Measure the Rough Opening

The rough opening is the space between the studs where the door frame will be installed. This measurement is important for ensuring a snug fit for a pre-hung door.

• To measure the rough opening, you’ll need to remove the interior trim or casing around the door. Once removed, measure from stud to stud for the width and from header to floor for the height.
• Make sure to measure at multiple points and record the smallest dimensions. The rough opening should be approximately 2 inches wider and 2 inches taller than the door itself to allow room for the frame and any adjustments during installation.

Pro Tip: If removing the trim is difficult, you can estimate the rough opening by adding 2 inches to the door’s width and height measurements.

5. Measure the Threshold or Sill Height

The threshold (or sill) height is another important aspect of how to measure for an exterior door, particularly if you are replacing the door. If your door sits on a high sill, it could impact the overall height of the door.

• Measure the distance from the floor or subfloor to the top of the threshold. This measurement will help determine if any modifications to the threshold or sill are necessary during installation.
• If the threshold is uneven or damaged, this is a good opportunity to plan for its replacement as well.

Pro Tip: Ensure the floor or subfloor where the door sits is level. An uneven floor may require adjustments to the threshold height.

6. Additional Considerations

• Swing Direction: Before purchasing a new door, confirm whether you need a right-hand or left-hand swing door. This is determined by the location of the hinges and how the door opens (inward or outward).
  
• Door Frame Condition: If your current door frame is damaged or warped, you may need to replace the entire frame along with the door. A new pre-hung door (which includes the frame) may be the best solution in this case.
  
• Weatherstripping and Insulation: Don’t forget about insulation and weatherproofing. When measuring for a new door, consider whether you’ll need additional space for weatherstripping, which helps seal gaps around the door and improves energy efficiency.
  

Common Measurement Mistakes to Avoid

• Not accounting for trim or molding: Ensure that the measurements you take are for the door itself, not the surrounding trim or casing.
• Ignoring the rough opening: Failing to measure the rough opening can lead to installation headaches later.
• Assuming standard sizes: While many doors come in standard sizes, always double-check your measurements, as older homes often have non-standard openings.

Elevate Your House With Our Doors!

Measuring for an exterior door is a vital first step in ensuring a seamless door installation. By following this guide on how to measure for an exterior door, you can confidently purchase the right door size, avoiding costly installation issues or energy inefficiency later on. 

Contact Alexandria Home Solutions today for a free consultation and discover the difference our doors can make.