Whether you're replacing an old door, installing a new one, or upgrading to a more energy-efficient model, knowing how to measure a door correctly is crucial. An accurate measurement ensures a proper fit, improves energy efficiency, enhances security, and avoids costly returns or modifications. In this guide, we’ll break down everything you need to know about how to measure a door, including exterior doors, screen doors, and door frames.
Why Accurate Door Measurement Matters
Before diving into the "how," it's important to understand the "why." A door that doesn’t fit properly can cause multiple issues:
- Drafts and energy loss
- Difficulty opening and closing
- Security vulnerabilities
- Aesthetic misalignment
- Extra costs from having to re-purchase or adjust materials
Tools You’ll Need
- Measuring tape (preferably metal for accuracy)
- Notepad and pen or smartphone
- Level (optional, for checking straight lines)
- Step stool or ladder (for taller doors)
How to Measure a Door: Step-by-Step Instructions
Step 1: Measure the Width
To begin, open the door and measure from the inside of one door jamb to the inside of the other. This is the door slab width, not including the frame.
- Measure at three points: top, middle, and bottom.
- Record the smallest measurement to ensure the door fits snugly.
- Common widths: 28", 30", 32", 36"
Step 2: Measure the Height
Measure from the floor (threshold) to the top of the door jamb (not the door slab).
- Measure at the left, center, and right sides.
- Take the shortest measurement.
- Standard door height: 80" (6 feet 8 inches)
Step 3: Measure the Thickness
Door thickness varies depending on the type of door.
- Most interior doors: 1 3/8 inches
- Exterior doors: 1 3/4 inches
- Screen doors: Varies, often 1 inch
How to Measure a Door Frame
Measure the Frame Width
Measure the distance from the inside edge of one side jamb to the other. Do this at the top, middle, and bottom.
Measure the Frame Height
Measure from the floor (or threshold) to the top inside edge of the head jamb.
Measure the Jamb Depth
This is the thickness of the wall that the door fits into. It’s critical for pre-hung doors.
- Measure from the inside edge of the interior trim to the inside edge of the exterior trim.
- Typical sizes: 4-9/16” for 2x4 walls, 6-9/16” for 2x6 walls
How to Measure a Door for Replacement
Option 1: Measuring the Existing Door Slab
Remove the door from its hinges and lay it flat. Measure:
- Width
- Height
- Thickness
Option 2: Measuring the Door Opening (Rough Opening)
If the entire frame is being replaced:
- Rough opening width: Measure stud-to-stud inside the frame
- Rough opening height: Measure from the subfloor to the top of the rough opening
- Add 2” to both height and width when purchasing a pre-hung door
How to Measure Exterior Door Accurately
Measure the Existing Door
If replacing only the door:
- Width, height, and thickness of the slab
Measure the Rough Opening
If replacing the entire system (door + frame):
- Measure the rough opening width and height
- Measure jamb depth to match your wall thickness
Pro Tip: Don’t forget to measure swing direction—whether it’s inswing or outswing, and whether it’s right- or left-handed.
How Do You Measure a Screen Door?
Measure the Door Opening
- Height: From the top of the door frame to the threshold
- Width: Inside edge to inside edge of the door trim
Determine the Mount Type
- Surface mount: Fits on the trim or outer edge
- Recessed mount: Fits within the door frame
Note: Be sure to leave room for hinges and handle hardware.
Common Mistakes to Avoid
- Measuring only the door slab and not the frame
- Ignoring jamb depth
- Rounding measurements (always measure to the nearest 1/16 inch)
- Forgetting to check if the door is square
- Not accounting for hardware placement and door swing
FAQs About Measuring Doors
How do I know if I need a pre-hung or slab door?
Pre-hung door: Comes with frame; ideal if your current frame is damaged or you want to change the size or type.
Slab door: Just the door panel; good for replacing a damaged door when the frame is intact.
What’s the rough opening for a standard 36-inch door?
Rough opening should be approximately 38” wide by 82” high to allow space for the frame and shimming.
Can I use the old door as a template?
Yes! If the old door fit well and you’re keeping the frame, you can use its dimensions as a reference when shopping.
Final Thoughts
Knowing how to measure a door accurately is an essential skill for homeowners, DIYers, and contractors alike. Whether you're learning how to measure a screen door, an exterior door, or simply trying to understand how do you measure a door frame, the key is precision. Always double-check your measurements, and don’t hesitate to consult a professional if you’re unsure.
By following this guide and using the right techniques, you'll ensure a perfect fit for your new door, improving your home's appearance, energy efficiency, and security.
