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    Video Tutorial 8:15 mins

    How to Measure Your Windows

    Accurate measurements are essential for a perfect fit. Follow our step-by-step video guide to measure your windows correctly.

    Video Coming Soon

    Our measurement tutorial video is currently in production

    Use Steel Tape

    Not fabric or plastic

    3x

    Measure Thrice

    At top, middle, bottom

    mm

    Use Millimetres

    For precision accuracy

    Video Timeline

    0:00

    Tools You'll Need

    Steel tape measure, notepad, pencil, and spirit level

    0:45

    Width Measurement

    Measuring the reveal width at three points

    2:00

    Height Measurement

    Measuring the reveal height at three points

    3:30

    Depth Check

    Ensuring adequate depth for the secondary glazing system

    4:45

    Squareness Test

    Checking diagonals to verify the window is square

    6:00

    Obstruction Check

    Identifying handles, locks, and other potential obstructions

    7:15

    Recording Measurements

    How to document and submit your measurements

    Common Mistakes to Avoid

    • ✕Measuring the glass instead of the reveal
    • ✕Taking only one measurement per dimension
    • ✕Forgetting to check for obstructions
    • ✕Not accounting for uneven reveals

    Prefer Written Instructions?

    Check out our detailed written guide with diagrams and a printable measurement sheet.

    View Written Guide

    Prefer a professional survey? We offer free no-obligation surveys.

    Book Free Survey

    Sources & References

    Authoritative sources supporting the information on this page.

    1. British Standards Institution (2014). Guidance on sound insulation and noise reduction for buildings (BS 8233:2014). BSI Standards.

      Sets the recommended internal noise levels for bedrooms and living rooms used to judge how much glazing performance a home needs.

    2. HM Government (2015). Approved Document E: Resistance to the passage of sound. The Building Regulations 2010.Open source

      The statutory guidance on sound insulation in dwellings in England.

    3. British Standards Institution (2020). Acoustics: Rating of sound insulation in buildings and of building elements, Part 1: Airborne sound insulation (BS EN ISO 717-1). BSI Standards.

      Defines the Rw and Rw+Ctr ratings used to compare the acoustic performance of glazing systems.

    4. British Standards Institution (2019). Glass in building: Glazing and airborne sound insulation (BS EN 12758). BSI Standards.

      Describes how the sound insulation of glass types, including acoustic laminates, is characterised.

    5. World Health Organization Regional Office for Europe (2018). Environmental Noise Guidelines for the European Region. World Health Organization.Open source

      Evidence-based guideline levels for road, rail and aircraft noise and their links to sleep disturbance and health.

    Measuring your windows accurately

    Why three measurements per dimension

    Period windows are rarely perfectly square, so the tutorial shows you measuring width and height at three points each. The smallest figure is the one that matters, because the unit must fit the tightest part of the reveal. Checking the diagonals tells you how far out of square the opening is.

    Depth is the measurement people forget most often. The reveal needs enough depth for the frame and for the air gap that gives secondary glazing its acoustic performance.

    • Measure the reveal, not the glass or the existing frame edge.
    • Note handles, locks and stays that could obstruct the new unit.
    • Send us your figures and we confirm everything at the free survey.

    Do not worry about being exact

    Your own measurements are only used to prepare an estimate. Final manufacturing sizes are always taken by our surveyor on site, so an approximate set of figures is perfectly fine to get started.