how to measure a door jamb

Woman standing In Front Of Her Doorway About To Take Measurements
Tools Needed
1 Paper
2 Pen
3 Pencil
4 Tape Measure
Materials Needed
1 Level
2 Safety Spotter
3 Ladder
4 Safety Glasses
Total Cost
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Estimated Time
5-10 Minutes
Skill Level: Beginner
The total cost and duration may vary when hiring a handyman!

Project Overview

person holding a tape measure across the width of a door slab

There are many reasons you might need to know the measurements of your door jamb. Maybe your are putting up new trim, or if you need to replace a door, you will want a snug fit and will need to know the measurements of your door jamb. Knowing the correct measurements of your door jamb is important so that you are able to order the correct door and frame size for your replacement.  You want to make sure that you get all of the dimensions needed, and you want these measurements to be as precise as possible.

Step-By-Step Instructions


Draw a Sketch

Before you start measuring, prepare yourself by grabbing a sheet of paper and a pen. If drawing makes you uncomfortable, you could also just print a picture from your computer. You want to use paper and get a visual because you need to be sure you are able to remember the exact measurements. Remember that you will be taking more than one measurement so it could get a little confusing, and if you are measuring so that you can replace something, you want to make sure your measurements are correct and as precise as possible.

Now, look at the door, and draw a rough sketch of the frame. Remember that this does not have to be perfect since it is just for your use. This sketch will give you an easy place to keep track of the measurements. Don’t just write the measurements where they belong on the sketch, but also label the measurements, like jam width, height, etc. This will minimize the possibility for any confusion.


Record Additional Details

Take notice and make sure that you are not including anything extra in your measurements. Take note of any door sweeps. Make sure that you are not including them in your measurements. Also, make sure you are not measuring any trim or weatherstripping. Just measure the jamb, nothing else. Other details you might want to consider are if this is right hand or left hand door and if it swings out or in.


Measure the Width of the Door Jamb

cross section of a door in a frame

Measure the jamb from side to side without including the trim. You want to measure the width three times to make sure you get the best possible measurement. On the diagram you drew in step 1, write the measurement. Once you have recorded it, round the measurement to the nearest inch, and write this number in parentheses beside the precise measurement. First measure the width at the top of the jamb, then the middle, and then the bottom. When you have taken all three measurements, take the lowest one and use it as your final measurement.


Measure the Height

person standing on the outside of their front door and measuring the height

Now, it is time to measure the height of the frame. To do this, you need two measurements. To take the first measurement, you will measure from the top left corner of the door all the way down to the bottom left corner on the floor. Record this measurement on your diagram. Next, measure the right side the exact same way, from the top right corner to the bottom right corner. Again, round both of these numbers to the nearest inch, and record them the same way you did the width of the door jamb. Take the lowest number, and use it to ensure you get a tight, insulated fit. If these measurements have a large difference, then now is probably a good time to check to see if your current door is crooked or if your floor is uneven.


Measure the Jamb Width

The final measurement you will need is the door jamb width, or wall thickness. Again, make sure that you do not measure any trim or other materials that are not the jamb itself. To measure the door jamb width, measure from the back of the interior piece of trim to the back side of the exterior. This measurement is important when replacing doors because the wrong sized jamb is pretty obvious. If the jamb is too small, your sheetrock will be exposed. If it is too thick, it will have to be trimmed down so that it doesn’t stick out.


Although measuring the dimensions of your door is not very difficult, you want to ensure you measure the right parts of the door and jamb, and you want to be sure you measure them correctly. You want to be careful, be precise, and take multiple measurements so that you do not purchase or order the incorrect sized door just because you were rushed. No matter what reason you have for measuring your door, you can be sure that you will measure correctly and precisely by following these steps.

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