Made-to-measure secondary glazing is only as good as the measurements behind it. This guide explains how to measure for secondary glazing accurately. Your guide price is based on the sizes you provide and is confirmed by a formal quote.
What you will need
- A steel tape measure that reads in millimetres
- A pencil and paper (or your phone) to note each window
- A spirit level or set square, to check the opening is square
- A step ladder for tall windows
Step-by-step: how to measure for secondary glazing
- Decide where the secondary glazing will sit. It is usually fitted inside the window reveal, on the room side of the existing window. Check that handles, locks, sash lifts, window boards, blinds and shutters will not be in the way.
- Measure the width of the opening in millimetres at the top, middle and bottom. Note the smallest measurement.
- Measure the height in millimetres on the left, in the middle and on the right. Note the smallest measurement.
- Check the opening is square by measuring both diagonals. If they differ noticeably, make a note, because older openings are often out of square.
- Measure the depth available in the reveal, from the face of the existing window (or anything that sticks out from it) to the room.
- Label each window (e.g. “Bedroom 1, left”) so sizes, styles and glass choices don’t get mixed up.
Give us the exact opening size: the smallest width and height you measured across the reveal. Do not make any deductions; we make any allowances needed. For supply & fit, we confirm every measurement ourselves when we survey.
Choosing a product type
- Horizontal sliders: for wider windows.
- Vertical sliders: for sash windows.
- Hinged / casement: full access to the window behind.
- Lift-out: for windows you rarely open.
- Fixed inserts: for windows that never need to open.
Each product page shows the size range available for an online guide price. For larger or unusual sizes, please request a quote.
Need help?
If you are unsure about any measurement, contact us or email quotes@thesecondaryglazingco.co.uk. Prefer not to measure yourself? Choose supply & fit. Fitting it yourself? See supply only DIY secondary glazing, then enter your sizes on any product page for an instant guide price and request a formal quote.