How to Measure for a New Composite Door – UK Survey Guide

Measuring for a new Composite door might seem daunting — but with the right method, it’s easy to get it right the first time. Whether you're a DIYer or a trade professional, this guide will walk you through how to measure accurately and avoid common pitfalls.

At The Plastics Shed, we supply complete composite door sets, including the outer frame — so it's essential to measure the brickwork opening, not the slab.

Step-by-Step: How to Measure for a New Composite Door

1. Only Measure for Full Frame Replacements

We don’t supply standalone slabs. Every door we offer comes with a fully-finished frame, so your measurements need to reflect the entire opening.

✅ Measure the full brick-to-brick space, not the current door panel.

2. Measure the Width

Take three measurements across the opening:

• Top

• Middle

• Bottom

Use the smallest of the three and deduct 10mm from each side for fitting clearance.

Use 910mm Measurement(smallest) and deduct 10mm = 900mm

3. Measure the Height

Again, measure at three points:

• Left

• Centre

• Right

Use the smallest height and deduct 10mm. If you're keeping the cill, include it in your measurement. If you're replacing it, measure from the base of the threshold up to the underside of the lintel.

Use 2079mm Measurement(smallest) and deduct 10mm - 2069mm

4. Decide on Opening Direction

• Stand outside the house facing the door

• Hinges on the left? It’s left-hand opening

• Hinges on the right? It’s right-hand opening

• Most doors are inward opening unless otherwise needed

• 
  

5. Things to Check Before You Order

✔ Are there any internal plaster returns that narrow the opening?

✔ Will the new door swing into furniture or radiators?

✔ Do you need a low aluminium threshold (for wheelchair access)?

✔ Are you matching the door style to an existing set of windows?

Still Not Sure?

Send us your measurements and photos, and we’ll double-check before you order. We’re here to help make the process stress-free.