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How do I know what size door I need?

December 22, 2022
3 minutes

To get the right size door for your property, you’ll need to measure the height, width and internal depth of the existing door frame which will give you the dimensions of the doors to fit your frame.

The first thing you need to know when you’re looking for a replacement UPVC or composite door is the exact size of the door to fit your frame. To make this job easier, this guide will take you through how to correctly measure your door frame.

This works for figuring out the size you’ll need for internal doors, a fire door, exterior door (such as french doors). To do this you’ll need a tape measure to take an accurate reading of the frame dimensions, and potentially a partner or family member to help with the height measurement which is normally the largest measurement you’ll be taking.

Things to remember when measuring your door frame

Measure the frame, not the door

It’s essential that when you’re measuring for a new door, you must always measure the frame, and not the door itself. It’s important to not rush this process, and a general rule is to double check and follow the age old adage “measure twice, cut once”. 

Check the direction the existing door opening

The second thing to look for is which direction the door opens. Take note of the hinges on the right or left side of the door when recording door measurements. If the door opens away from you, stand in front of it, and observe whether they are on the right or left side. A left hand side hinge indicates that the door is open to the left, whereas a right-hand hinge indicates that the door is open to the right.

How to measure a door frame

Step 1: Measure the width of the door frame

Take three measurements inside the door frame – at the top, middle and bottom. The widest width measurement determines the width of the door.

  • Measure the width of the door frame across the 3 points, the top, the middle and the bottom. 
  • The highest width of the door frame determines the width of the door you’ll need.
  • An average standard size width of doors in the UK are: 24 inches/610 mm, 27 inches/686 mm, 30 inches/762 mm and 33 inches/838 mm.

Step 2: Measure the height of the door frame

Measure the inside of both vertical sides of the door frame. The tallest length of the door frame determines the height of the door required. Remember to make allowance on the floor or for any carpet or flooring.

When measuring the height of the door you may need a step ladder to reach the top of the frame.

  • Use a tape measure to measure the door height of the frame. Record the longest length from the top corner to the bottom corner on each side.
  • The average height of standard door sizes in the UK is 1981mm but some may also be 2040mm.

Step 3: Measure the thickness of the Internal door frame

One thing which is often forgotten is the thickness of the door frame. 

  • Use a tape to measure the inside thickness of the door frame (this is where the door sits in when closed).
  • If you have the existing door with you then measure the thickness of this too. Both of these measurements should be a close match.
  • In terms of standard size, 35mm is the most common thickness but some can also be 40mm or higher. For a door width of 45m or above this is usually for fire doors.

Select a replacement door with the right dimensions for your property 

You’ve now got all 3 measurements for the door thickness, width and height that you need and you can look for the best door to fit your home’s frame. We’ve got a wide range of used doors to choose from including UPVC Front Doors, UPVC Back Doors, Composite Front Doors, Composite Back Doors, Stable Doors and French & Patio Doors

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