Measuring an internal or external door isn’t as tricky as it might seem, and our easy-to-follow guide will take you through the steps. Whether you’re building your own home or upgrading tired internal doors, this is a task any DIYer can handle with a little care and the right tools.
Top tip: Always take at least two sets of measurements to confirm accuracy. The last thing you want is a door that doesn’t fit when installation day arrives.
How To Measure for New Internal Doors
Start by measuring your existing doors. Most internal replacement doors come in standard height and width sizes, so you’ll want to choose the one closest to your existing door. If in doubt, always choose the slightly larger standard size — this allows your fitter to plane the door to fit perfectly.
Steps:
- Select a size slightly larger than your current door to accommodate on-site adjustments.
- Remember that all homes are different — door frames may vary slightly, so planning may be needed.
- New internal doors must meet minimum height and width standards set out by UK Building Regulations.
What You’ll Need
- Tape measure
- Notepad, phone or measuring sheet to record measurements
Measurements You’ll Need to Take
Door Height:
- Measure inside the frame, from top to bottom.
- Measure both the left and right sides.
- Avoid measuring to the floor directly — leave clearance for flooring.
- Use the tallest of the two measurements.
Door Width:
- Take three measurements: at the top, middle, and bottom of the opening.
- Measure inside the frame.
- Record all three and use the widest as your final width.
Door Thickness:
- Measure from the inside edge to the outside edge of the door frame.
- Repeat twice to ensure accuracy.
- Standard door thicknesses are 35mm, 40mm, and 45mm. If upgrading to a thicker door, simply adjust door stops and hinge recesses to suit.
Measuring External Doors
Measuring for an external door (e.g. front or back doors) differs slightly. It's crucial that at least one external door meets the 775mm clear opening requirement and has an accessible threshold, as specified in Part M of the UK Building Regulations.
How to Measure an External Door:
Door Width:
- Measure across the top, middle, and bottom of the door opening (including the frame if you are replacing it).
- For older properties where measurements may vary, choose the largest measurement.
- It's easier to trim down a slightly larger door than replace one that’s too small.
Door Height:
- Measure the left and right sides of the opening.
- Record both and select the taller of the two.
Door Thickness:
- For existing doors, measure the thickness when the door is open.
- For new builds, use the intended frame thickness for reference.
Important Tips for External Doors
- Plan to sink your door set cill slightly into the floor to reduce the number of steps.
- Always measure from the external side of an existing door.
- If render or plaster is hiding the frame, you may need to create a small inspection hole for an accurate measurement.
Ordering New Doors Online
Online listings usually show measurements as height x width x thickness. At Mumford & Wood, all of our timber doors are made to measure, taking the hassle out of finding the perfect fit for your home.
UK Standard Internal Door Sizes
- 1981 x 610/686 x 35mm – Ideal for smaller spaces
- 1981 x 762 x 35mm – Common UK size (also known as 2'6")
- 1981 x 838 x 35mm – Often used for wheelchair access (also called 2'9")
UK Standard External Door Sizes
- Standard height: 2090mm
- Standard widths: 890mm or 1000mm
Explore Mumford & Wood's Door Range
Looking for premium timber doors? Whether it’s internal doors, entrance doors, patio doors, or bifolds, we offer beautifully crafted solutions tailored to your space.
About Mumford & Wood
At Mumford & Wood, we pride ourselves on crafting bespoke, sustainable timber doors and windows that stand the test of time. We use the finest materials and expert craftsmanship to ensure quality, durability and elegance.
If you’re interested in premium timber doors for your property or development, download our brochure or request a physical copy online for more inspiration.
