How to fit a New Door into an existing Door Frame (Step-by-Step DIY Guide)

Need a new door and want to match it to your existing style and door frame? Here is what you need to know. Replacing a door doesn’t always mean tearing out the entire frame. If your current door frame is still in good shape, you can install a new door slab to fit perfectly — saving time, money, and effort. In this guide, we’ll walk you through how to fit a new door into an existing frame like a pro, even if you’re doing it yourself for the first time.

Inspect the Existing Door Frame

When considering new doors for your home or business, it is not always necessary to change out the old door frame. First, inspect your existing door frame for damage or rot around the edges and bottom. Next, test the door frame if it is square and plumb; measure both diagonals of the opening and they should be the same length. To check if a door frame is plumb, hand a weighted string from the top of the frame, the string should be parallel with the door. If the frame is warped or damaged, replace or repair it before fitting a new door. 

If the existing door jamb is intact and strong, it can be reused. Although, we at Interbay Door would be happy to supply you with a pre-hung door with new jambs, we are also able to machine new doors to match existing door frames. To match a door slab, we will need some key measurements from you. See below what measurements we need and how to make them, as well as a couple of tips we have for you on understanding your new door slabs. 

Take Accurate Door Measurements

The key to a good fit is precise measurements. Swing doors have a bevel cut on one edge so that they open and close easily in a square jamb. If there was no bevel, the door wouldn’t be able to open as it would fit so snug into the jamb. The bevel also means that width of one side of the door is shorter than the other. 

 Width: Measure the door slab itself (on the closed side where you can see the barrel of the hinge) at the top, middle, and bottom. Also, make sure to do the same in the existing frame. 

Height: Measure from the floor to the top of the jamb on both sides. As well as from the top of the door itself to the bottom of the door. As many older doors have been cut down and re-hung due to carpet installation or other flooring materials that are later removed, it is not always helpful to only know the height of the door slab itself as they can be shorter than what is needed. If you do have a gap between the existing door and the floor that you would like to tighten up with the new door, please let us know how much.

Thickness: Measure the thickness of your current door. Most interior doors are 1-3/8” thick and exterior doors are 1-3/4” thick. 

Choose the Right Door Slab

When replacing just the door (not the frame), you’ll need a door slab. We can help you with your new door slab, we will just need some information and measurements from you. 

Style: Would you like to match your home’s existing design? Send us pictures and details about the doors’ finish, style, material and door construction (molded, stile and rail, or flush). For inspiration, see our blog about door construction. Pictures that are helpful for us, at Interbay Door, to see are pictures like below: 1) Full size picture that shows the style of the door, 2) close-up picture so we can see texture and style of construction, 3) the door jamb plate so we know how to prep the jamb, 4) the door edge prep, and 5) the hinge side of the door.

Swing: Make sure your new door opens the same way as the old one. See the swings below. At Interbay Door, we are more concerned about where the hinges are located when it comes to the swing handing. When you are on the side of the door where you can see the barrels of the hinges and are pulling the doors towards yourself, which side are the hinges on? Your left, or right? 

 Measurements: When matching your hinge and door knob location, we will need location measurements for each. Always starting with your measuring tape at the top of the door, measure to the top of each hinge – top, middle, and bottom. At Interbay Door, if you bring us your old door slab, we are also happy to match the old hinge, bore and latch styles and locations to your new door. However, if this is an inconvenient door to remove for any period (like a common area bathroom door), please see the below instructions for the measurements that we will need and how to do so. 

Note the size (common sizes are 3.5” and 4” H), screw pattern (D or S pattern for 4” or bigger only) and corner detail (5/8” radius, ¼” radius or square) of the hinges.

Measure the location of the knob bore (and deadbolt bore, if available) from the top of the door to the middle of the knob. Do the same for the latch, measure from top of the door to the center and note the style of the latch style (drive-in, square, or rounded). Measure the size of the bore holes for knobs and/or deadbolts, commonly 2-1/8” in diameter.

Finishing Touches

Once your door has arrived at Interbay Door, been machined to match and is delivered to the site, it is time to transfer your hinges, hardware and test fit your new door. Hang your new door and check for smooth opening and closing. Look for any gaps around the edges that should be even about an 1/8”. Make sure to plan and sand any tight areas. Once that is done, your new door is ready for a finish. 

Matching a new door to an existing frame is one of the most rewarding upgrades. It can completely refresh your space without the cost or mess of full-frame replacement. With the right measurements and a bit of patience, you’ll achieve a smooth, professional fit that looks great and works perfectly.

At Interbay Door, we have been providing quality doors, hardware and millwork to the Greater Seattle area since 1990 and are ready to help you start your next project. 

Give us a call at Interbay Door (425-485-6404 or info@interbaydoor.com) today!