How to Replace a Prehung Interior Door: Measuring, Ordering and Installing

Replacing an interior door is one of the most satisfying DIY upgrades, and a prehung door makes it much easier. The door arrives already hung in its frame, so you don't have to chisel hinge mortises or fight to get an even gap. The key is ordering the right unit. This guide walks you through measuring, choosing and installing a prehung interior door.

Prehung vs. Slab: Which Do You Need?

A slab is just the door. For example, our 28" x 80" White Shaker 2-Panel slab is sold with no bore hole or hardware. Choose a slab if your existing frame is square, solid and in good shape, and you're comfortable matching hinge locations.

A prehung unit includes the door, the jamb (frame) and the hinges, already assembled. Choose prehung if:

• The old frame is damaged, out of square or painted over too many times
• You're changing the door size or swing
• You want the most predictable, professional-looking result

Step 1: Measure Your Opening

1. Door size: measure the width and height of the existing door slab. Doors are named by slab size, so a "30-inch door" has a 30"-wide slab. For standard widths and heights, see our Standard Interior Door Sizes guide.
2. Rough opening: remove the casing on one side and measure the framed opening, stud to stud and floor to header. The new unit's overall frame size has to fit inside this, with a little space left for shims.
3. Wall thickness: measure from drywall face to drywall face. This determines your jamb width.

Compare to the listed unit size

Product pages often list overall dimensions with the frame. For example, our 32" x 80" Shaker 5-Lite prehung door lists 33.5" x 81.5" with the frame. Compare that to your rough opening before you order. Need help? AAA Doors offers a free measurement request.

Step 2: Check Jamb Width

Our white Shaker prehung doors come with an unfinished finger-jointed pine jamb that is 4 5/8" wide. That width is commonly used for walls framed with 2x4 studs and drywall on both sides. If your wall is thicker, such as plaster or a 2x6 wall, you'll need jamb extensions. Measure first.

Step 3: Choose Handing (Swing Direction)

Handing tells you which side the hinges are on. Stand on the side the door swings toward you (the push side is the other side):

• Hinges on the left = left-handed
• Hinges on the right = right-handed

On our prehung Shaker doors, the left- and right-hand selection assumes an in-swing, but the doors are reversible for an out-swing. When in doubt, take a photo of the opening showing the hinges and ask us before ordering.

Step 4: Pick Style and Hinge Finish

One of our best-selling prehung units, the 32" x 6'8" White 2-Panel Shaker, comes with hinges in satin nickel, black or oil-rubbed bronze. It's single-bored for a standard knob or lever. Not sure which panel style you want? Compare Shaker interior door styles.

Step 5: Remove the Old Door and Frame

1. Remove the door from its hinges.
2. Carefully pry off the casing on both sides. Save it if you plan to reuse it.
3. Cut through the nails or shims holding the old jamb (a reciprocating saw works well) and remove the frame.
4. Clean up the opening and check that the floor is level across it.

Step 6: Install the Prehung Unit

1. Set the unit in the opening with the door closed, centered and flush with both wall faces.
2. Plumb the hinge side first. Shim behind each hinge location until the hinge jamb is perfectly plumb, then nail through the jamb and shims into the framing.
3. Shim the latch side and head to keep an even gap around the door. Check that the door swings freely and latches.
4. Secure the hinges. Many installers replace one screw in each hinge with a longer screw that reaches the framing, especially for heavier solid core doors.
5. Trim the shims flush and fill the gap with low-expansion foam if desired.

Step 7: Casing, Hardware and Paint

Reinstall or replace the casing, install your knob or lever from our interior door handles, and paint. Our doors come primed white, and the pine jamb is unfinished, so it can be painted or stained.

Wondering whether solid core is worth the extra weight? Read solid core vs. hollow core doors. Replacing a wider opening? See our guide to interior French doors.

Frequently Asked Questions

Is it hard to install a prehung door?

It's a manageable DIY project for most handy homeowners. Getting the hinge side plumb is the most important step. Take your time with shims.

What size prehung door do I need?

Order by slab size (for example, 30" x 80") and confirm the unit's overall frame size fits your rough opening.

Can I reuse my old casing?

Often, yes, if you remove it carefully. New casing gives the cleanest result.

Do you offer installation?

AAA Doors works with installers, and you can request a free measurement. Contact our team to ask about your area.