SEARCH:
Made to Measure • Online Quotes • Technical Support

Secondary Glazing Made Simple

• Easy DIY Installation • Reduce Heat Loss • Cut Outside Noise • Save On Energy • Delivery Within 10 Days*
Get Instant Price Browse Systems
20% off 10 year guarantee

How to Measure for Secondary Glazing

This guide is here to help you take clear, practical measurements for your secondary glazing. Whether you are measuring inside the reveal, fixing over the reveal, matching existing bars or planning a bay window, the aim is to make the process straightforward and easy to follow.

Every opening is slightly different, so use this page as a practical guide and always apply your own judgement on site. Where needed, take several measurements, check for out-of-square openings, and work from the tightest sizes.

Before You Start

Have the right approach before you pick up the tape measure.

  • Take multiple width and height measurements rather than relying on a single point.
  • Check whether the reveal is square, level and free from obstructions.
  • Use the smallest tight measurement where appropriate.
  • Allow a sensible fitting tolerance to suit the installation.
  • Where existing bars need to line through, measure to the centre point of those bars.
As a general guide, many customers allow 6mm off both the width and height, giving an approximate 3mm gap around the product. This is guidance only and may need adjusting to suit the actual opening and installation conditions.

Measuring Within the Reveal

For installations where the secondary glazing sits inside the existing reveal.

Secondary glazing measuring guide within the reveal

Measuring to Fix Over the Reveal

For installations where the secondary glazing is face fixed over the opening.

Measuring Splits

Used where bars need to align with the existing prime window.

Measuring a Bay Window

Plan each section carefully before arriving at final secondary sizes.

Typical Frame Size Guide

A simple quick-reference section for common frame options.