How to Measure A Door: The Right Way and The Wrong Way.

Why should you measure your door?

Measuring for a replacement door is an easy task that should be done before you start looking. Having this information can help narrow down your options when searching, as not every type of door will work with your space. If you are seeking a quote or advice from a professional, having this knowledge will help them give you more accurate suggestions about what options are available for you and make the process more streamline.

When measuring for either a new or replacement door, there are a few considerations you want to take into account. To help you measure like a pro, we have compiled information about where you should be taking your measurements based on the type of door you have.

Determine What You Are Measuring For

The easiest and most overlooked step in this process is determining what you are measuring.

You must conside: Are you measuring your prehung door unit, your door slab, or sliding doors.

Prehung door unit 

Your prehung door unit is your door with the hinges and frame already attached. They will fit nicely into a prepared doorway, and are a little more expensive but easier to install.

There are interior and exterior units, but the main difference between those is the exterior trim. The exterior trim is on the outside of the doorframe and is usually a brickmould or casing. They work as an accent to compliment the door and tie everything together.

Measuring a Prehung Door Unit 

When measuring a prehung door unit you are mainly focusing on the door frame. How you measure will also differ based on if you are replacing a door or installing into a rough opening.

Replacing a Door: 

  1. Start by removing the trim on one of the sides of the door.
  2. Measure the width of the frame. When measuring the door frame, you want to measure the frame itself, not the opening where the door would go. You will want to measure across the top, middle, and bottom and then choose the smallest measurement.

                                                        (Construction Blog)

3. To measure the height, start at the floor or “threshold” for an exterior door, and measure up to the top edge of the door frame.

4. Measure the width of the side of the frame (side jamb) from the exterior to the interior. Do not include the exterior trim.

                                                                          (kills Institute Press LLC)


5. When you replace a door unit, there is an opening in the siding. You will want to measure the height and width of the trim frame to fill this.

6. Measure your door swing (Visit below)

Installing into a rough opening

The rough opening is the just the hole that is created in the side of a wall for a door to be installed.

  1. Measure the inside width of the opening. As mentioned before, measure in the three spots (top, middle, bottom) and use the smallest measurement.
  2. Repeat the first step for the height of the rough opening.
  3. To get the thickness of the wall, measure the width of the drywall where the rough opening is
  4. Measure your door swing (visit below)

Door slab

Your door slab is just the door itself without a frame or hardware. If you are just looking to replace the door and nothing else, this is how you should measure it.

 Measuring a Door Slab 

  1. Ensure the door is closed and stand on the same side as the hinges.
  2. Measure the door vertically and horizontally, leaving out the door frame.
  3. Measure the thickness of the door by opening it, and measuring it from front to back.
  4. Determine your door swing by standing with your back against the hinges. if your left hand is closest to the door knob, then it is a left swing door, and vice versa for the right side.

Measuring sliding doors 

If you are looking to replace your sliding doors, or thinking about installing sliding doors, this is how you should measure it.

  1. You want to begin by measuring the entire width of the door, from outside edge to outside edge.
  2. Repeat the same process vertically.
  3. Measure just the door itself horizontally, to see how much room you have for the door to slide open.

Measuring your door before you start searching will help you save you time and avoid costly mistakes when it comes to ordering a door. Before making any final decisions, it is still good to have a professional look it over to ensure you have the right information needed to find the perfect fit. Good luck, happy home renovating!




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