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The Heritage Collection / Doors  / How do I measure up for my new door?

How do I measure up for my new door?

How To Measure a Door Opening 

Here at Heritage, our speciality is custom products. This is brilliant news for those with old, characterful houses needing more than standard sizes can offer. However, this means you must be very accurate when measuring up for the size you require. We have put together a step-by-step guide to ensure this process is as easy as possible!

Measure your door

Are there differences between the way to measure internal and external openings?

There are a few differences between the two, however the general basis is the same!

How to Measure a Door For External Use

For external openings, your frame will most likely include a cill at the bottom.

How to Measure a Door For Internal Use

Whereas, internal frames will only be on the top and sides. This does not make a major difference to how you measure, but it is something to be aware of if you are shopping for a replacement frame also.

How To Measure A Door: How easy is it to do?


For precise measurements, we recommend taking all measurements in mm.

  1. Ensure you are measuring frame to frame in your opening for the width. Your tape measure should go essentially where the door would sit. We recommend taking 2-3 different measurements, ideally at the top, middle and bottom of the opening as some openings are not exactly square.
  2. Record your biggest measurement for the width*
  3. Now you need to do the same for the height. For an internal opening, there will be no frame at the bottom. So you should measure from your frame at the top (where it ends), to the floor.
  4. For an external door, you will need to measure from the frame at the top, to your where the sill begins. So again, essentially where the door would sit.
  5. Measure either side of your opening to ensure one side is not bigger than the other
  6. Record your biggest measurement for the height*
  7. Take your biggest width and biggest height measurement.
  8. Now you should subtract 2mm from each side
  9. Simply order your door, and pop in your measurements at checkout! We will make the door to exactly the measurements you specify, so please ensure your measurements are accurate by double checking beforehand


(Total width) – 4 = Door width needed in mm
(Total height) – 4 = Door height needed in mm

*Our doors can be trimmed on site by most joiners for openings which are not exactly square. For angled openings, we have angle top doors available!

Contact Us

For any further advise or guidance on how to measure a door or door opening, please get in touch!

Call us on 01142474917, email us at, or message us on our facebook page!