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How to Measure for a Prehung Door? (Step-By-Step Tutorial)

How to Measure for a Prehung Door? (Step-By-Step Tutorial)

Many homeowners prefer prehung doors when looking for exterior doors. The reason is that these doors come with a frame already attached to the door, making the installation a lot easier. Apart from that, prehung exterior doors are more weather tight compared to other door types.

However, for you to purchase the perfect size prehung door, you need to get the size of the rough opening doorways. For this reason, you need to know how to measure the rough opening. But if you don’t have an idea, our detailed steps on how to measure for a prehung door will guide you.

Tools Required

  • Utility knife
  • Painter’s pry bar
  • Plastic or wooden shim
  • Tape measure

Steps for Measuring a Prehung Door

Step 1: Take Out the Trim from Door Rough Opening

Take Out the Trim from Door Rough Opening

The rough opening is the space where you install the door. As for the trim, also known as molding, is the material that surrounds the rough opening. So, for you to measure for a pre-hung door, you should remove the trim from the door.

Step 2: Ensure the Door Studs Stay Level

Ensure the Door Studs Stay Level

The door studs are beams found at the back of the door molding. If the stud vertically stays more than 1/4 out of plum, try to level it out. By doing this, it is easier to get an accurate measurement of the rough opening.

Step 3: Measure All the Sides of the Rough Opening

Measure All the Sides of the Rough Opening

  • Get the Width of the Rough opening: To get the width, you will need to measure the door stud at the opposite side of the doorway to the other end of the opening. Ensure your measurements are in inches.
  • Get the Height of the rough opening: Take your measurements from the floor surface to the uppermost part of the rough opening.
  • Measure the depth of the rough opening: To get the depth, measure from the front edge of the opening to the back edge.

Step 4. Use the Measurements to Purchase a New Pre-hung Door

Use the Measurements to Purchase a New Pre-hung Door

After making the measurements, take your recordings and head to a hardware store. With the measures, you can find a door that fits.


How to Measure to Replace a Prehung Interior Door

If you plan on changing the prehung interior doors in your home, you will have to take proper measurements of the frame.

Step 1. Remove the Outer part of the Interior Door Casing

Remove the Outer part of the Interior Door Casing

Insert the bottom of a painter’s pry bar into the space between the door casing and the wall. To avoid damaging the walls, insert a plastic or wooden shim between the bottom of the pry bar and the wall.

Use the pry bar to pull out the casing from the door trim. At this stage, gently work the outer part of the door trim. Continue until you have prayed out the doorcase at the upper part, left, and right side. As you work, do not need to take out casing at the same time from both ends of the door frame.

Step 2: Get the Height, Width and Wall Depth of the Door Opening

Get the Height, Width and Wall Depth of the Door Opening

If you want to get measure the width, head to the top of the door frame and measure from stud to stud. Afterward, measure from stud to stud at the center and lowest part of the frame. Write down the smallest measurement.

To get the height, measure from the topmost part of the frame to the floor surface near the right end of the frame. Then take your tape to left end of the door opening and from the top part to the floor surface again. Write down the smallest measurement of height you have gotten.

Round up by measuring the jam depth.  The jam depth is the width of the wall. Most jam depths measure 4 9/16 or 6 9/16 inches.

Step 3. Create a Table and Write Down all the Measurements

Create a Table and Write Down all the Measurements

Record the measurements taken in the steps above – the smallest height, width, and wall jam depth. Also, when learning how to measure for a prehung door, also record the width, thickness, and height of the door and its frame.

If you are getting these doors in multiples, but different sizes, it’s best to create a prehung door opening chart and record your findings.


Tips for Buying a Pre-Hung Door

1. Choose a Door Frame that Fits the Opening

When purchasing a prehung or pre-hinged door, ensure that the rough opening is a little larger than the outer dimensions of the door itself. That way, it is easier to add a shim to level the door for installation.

2. Consider the Width of the Jambs

Consider the Width of the Jambs

Door frames consist of three pieces which include the jambs. When measuring for a prehung door, you must size the jambs to the finish depth of your door-opening.

A door jamb of 4 9/16 inches is usually the popular option, and they are made for a wall frame of 1/2inch drywall with 2×4 lumber on both sides.

3. Know the Direction of Your Door Swing

To find the door swing, you will need to face the door while looking inwards. You can determine which part goes inside by checking for exposed hinges. The hinges are usually on the inner part of the door.

If the doorknob stay on the right side and open in your direction, it means you have a left-hand swing. But if the knob is at the left and opens towards your body, the door has a left-hand swing. Although most exterior doors swing inwards, some companies offer models that swings out. Before hitting the stores, put “outswing” and “inswing” on paper.

4. Type of Prehung Door

Type of Prehung Door

There are various types of prehung doors – the wood, fiberglass, metal, or one made with wood composites. If you want to choose based on style, you can pick between stain grade or painted grade doors.

You can also select between the more solid core models or settle for the hollow core models that are lighter and affordable. If you want extra lighting in your room, you can go for a pre-hung door with sidelight.

5. The Space for Door Knobs

Some prehung doors have holes for doorknobs. Since most doorknobs come in a standard size, there is no need to bother about the size and location of the knob hole. However, some vintage or expensive knobs tend to comes in different bore sizes.

To avoid any problems, get your preferred knobs before ordering for the prehung doors. Ensure the door has a bore that will your purchased knob perfectly.


If you use prehung doors, you might want to replace them or fix new ones. For this reason, you need to know how to measure for a prehung door purchase. Aside getting the accurate measurement, you will have to use these following tips to get a prehung door that meets your taste.

  • Choose a door frame that fits the opening.
  • Consider the sizing of the door jamb
  • Find the direction of the door swing.
  • Go for a prehung door of your choice.
  • Make sure the doorknob matches the bore on the door.

That wraps up the article, we hope you find the guide useful. If you have any questions about, please feel free to use the comment space below.