Replacing a door can update the look of your home, improve privacy or address wear and damage. Before choosing a replacement, though, you need to know which dimensions will fit your existing doorway.
Measuring a door involves more than checking its width and height. You’ll also need to account for door thickness, jamb depth and, when replacing the entire door unit, the rough opening. Door swing and handing matter, too, since they determine how the new door will operate in your space.
Whether you’re replacing an interior door or upgrading an exterior entry, this guide walks you through the measurements to take and the details to have ready before ordering.
Should You Replace Just the Door Panel, or the Entire Assembly?
A slab is the door panel by itself. A prehung door arrives already mounted in its own frame with the hinges attached, ready to install in the opening.
The condition of the existing frame usually determines which option makes sense. If the frame is solid, square and free of rot or warping, you may be able to replace just the slab. If the jamb is damaged, out of square or too narrow for the wall, a prehung unit replaces the entire assembly. Florida humidity can swell and soften wood jambs, so check the bottom of each jamb for soft spots, especially in bathrooms and laundry rooms.
Use a level to check whether the door frame is plumb, meaning its sides run straight up and down. Then measure diagonally between opposite corners of the opening, from the top left to the bottom right and from the top right to the bottom left. If the two measurements match, the opening is square, meaning its corners form right angles. If the frame is damaged or the measurements differ, have the opening assessed before deciding which replacement option to choose.
How to Measure a Door for Replacement
Gather a metal tape measure, a pencil, a level and something to write on. Record each measurement to the nearest 1/16 inch, labeling it by location, such as “width, top” or “height, left.”
Step 1: Measure the Door Width
Measure the door slab from one edge to the other, leaving the frame and trim out of the measurement. Take the reading at the top, middle and bottom of the door and write down all three. If they differ, note the variation rather than choosing the nearest standard size. Share the readings with your door supplier to determine which replacement dimensions will work with the existing frame.
Step 2: Measure the Door Height
Measure the slab from top to bottom on both the left and right sides. Floors and frames settle unevenly, so the two readings may not match. Record both. If you’re planning new flooring, note its thickness, since it changes the clearance under the door.
Step 3: Measure the Door Thickness
Measure across the edge of the door from one face to the other. Most interior doors are 1â…ś inches thick, and some solid-core and fire-rated doors measure 1Âľ inches.
Thickness determines which latch and lock hardware fits, so it’s also the first number to check before adding a smart lock or other electronic hardware. Doors between an attached garage and the home have their own thickness and rating requirements.
Step 4: Measure the Jamb Depth (Prehung Doors)
Jamb depth is the depth of the door frame across the wall thickness. It needs to accommodate the finished wall so the frame and trim fit properly.
Measure from one finished wall surface to the other, including the drywall on both sides but excluding the decorative casing. If the trim prevents you from identifying the correct measurement points, have an installer verify the wall thickness before ordering.
Two sizes cover many interior walls: 4 9/16 inches for a 2-by-4 wall with half-inch drywall on each side and 6 9/16 inches for a 2-by-6 wall with the same drywall thickness. Block construction, common in Florida homes, and walls with thicker finishes can require different jamb depths, so measure the wall rather than assuming a standard size.
Step 5: Measure the Rough Opening (Prehung Doors)
The rough opening is the framed hole in the wall that holds the prehung unit. It’s larger than the door so there’s room to shim the frame plumb and level. Remove the casing to expose the framing, then measure the width between the studs at the top, middle and bottom. Measure the height from the floor to the underside of the header on the left, middle and right, and note the thickness of any finished flooring.
For many standard interior prehung doors, the rough opening is approximately 2 inches wider and 2½ inches taller than the door slab. For example, a 30-by-80-inch door typically requires a rough opening of about 32 by 82½ inches. These dimensions are a general guideline, so check the manufacturer’s installation specifications before ordering, especially for exterior entry doors.
| Measurement | Where to Take It | Slab Swap | Prehung Unit |
| Width | Slab edge to edge at the top, middle and bottom | Yes | Yes |
| Height | Slab top to bottom on both sides | Yes | Yes |
| Thickness | Across the door edge | Yes | Yes |
| Jamb depth | Finished wall surface to finished wall surface | No | Yes |
| Rough opening | Stud to stud, floor to header | No | Yes |
| Swing and handling | Record hinge location and swing direction from the appropriate viewing position | Yes | Yes |
Door Swing and Handing
Door swing describes the direction a door opens, while handing is the door’s hinge-side configuration. Both details belong on the order because a replacement with the wrong handing may not work with the existing frame or fit the intended opening.
To identify your door’s configuration, note three things:
- Swing direction: Does the door open into the room or away from it? For an exterior entry, note whether it swings into or out of the home.
- Hinge location: Are the hinges on the left or right side of the door?
- Viewing position: Which side of the door are you standing on when identifying the hinge location?
For interior doors, the common method is to stand on the side where the door swings away from you. If the hinges are on the left, it’s generally a left-hand door; if they’re on the right, it’s generally a right-hand door. Confirm the handing convention with your supplier before ordering.
For exterior doors, stand outside facing the door from the entry side. Record whether the door swings inward or outward and which side the hinges are on. Exterior doors are designated by both handing and swing direction, such as left-hand inswing. Your supplier can confirm the correct designation for your selected door.
If you’re replacing only the slab, make sure the new door’s hinge and latch locations match the existing frame. Taking photos of the door from both sides can also help your supplier verify the configuration.
What to Have Ready When You Order a Replacement Door
Gather these details before you contact a supplier:
- Slab swap or prehung unit
- Width, height and thickness of the existing door
- Jamb depth and rough opening, for prehung units
- Swing direction and handing
- Room and location, including whether the door opens to a garage and needs a fire rating
- Hardware details, including the lockset type, hinge size and backset (the distance from the door edge to the center of the lock hole)
- Preferred style, core construction, finish and glass, if any
- Photos of the door, frame and hardware, with the tape measure visible to show each reading
Replace Your Door With 1st Choice Door & Millwork
At 1st Choice Door & Millwork, we help Central Florida homeowners, builders and investors choose doors, trim and hardware for their projects. Whether you’re replacing an interior door, upgrading your front entry or planning a larger renovation, our team can help you find the right options for your home.
Ready to get started? Contact us today.
