Replacing your windows is one of the best ways to improve your home’s energy efficiency, security and appearance. Whether you’re renovating your property or upgrading ageing windows, getting the measurements right is the first and most important step.
If you’re wondering how to measure windows for replacement, don’t worry—it doesn’t have to be complicated. With a tape measure, a few simple checks and our step-by-step guide, you’ll have everything you need to order your new made-to-measure windows with confidence.
Why Accurate Window Measurements Matter
Made-to-measure windows are manufactured specifically for your property. Accurate measurements help ensure:
- A precise fit
- Better thermal performance
- Improved weatherproofing
- Easier installation
- A professional finish
Taking a little extra time to measure correctly can save both time and money later.
What You’ll Need
Before you begin, gather the following:
- Steel tape measure
- Pencil and notepad
- Spirit level (optional)
- Step ladder (if required)
- Another person to help with larger windows
Always measure in millimetres (mm), as this is the standard unit used for replacement windows.
How to Measure Windows in 5 Simple Steps
- Measure the Width
Measure the window opening in three places:
- Top
- Middle
- Bottom
Record all three measurements.
Use the smallest measurement as your overall width.
This accounts for any slight variations in the brickwork or existing opening.
- Measure the Height
Now measure the height of the opening from:
- Left side
- Centre
- Right side
Again, use the smallest measurement.
- Check the Window Opening Is Square
Although not essential, checking for squareness is recommended.
Measure diagonally from corner to corner in both directions.
If both measurements are very similar, the opening is square.
If there’s a significant difference, it may be worth consulting your installer before ordering.
- Measure from the Outside
Where possible, measure the brick opening from the outside of the property rather than relying solely on the internal frame.
This provides a more accurate indication of the replacement window size required.
If access isn’t possible, internal measurements can still provide a good guide.
- Double Check Everything
Before placing your order:
- Measure everything again.
- Check every figure carefully.
- Make sure you’ve recorded measurements in millimetres.
It’s always better to spend another five minutes measuring than discover an issue once your windows have been manufactured.
Measuring Different Types of Windows
Although the measuring process is broadly the same, different window styles can require extra attention.
Casement Windows
Measure the overall structural opening, not the opening sash.
Flush Casement Windows
The same principles apply, but always measure the existing opening rather than the visible frame.
Bay Windows
Bay windows can be more complex because of the angles involved.
For these installations, professional measuring is often recommended to ensure every section fits perfectly.
Common Mistakes to Avoid
When learning how to measure windows, these are some of the most common errors homeowners make.
Measuring the Existing Frame
Replacement windows are manufactured to fit the opening—not necessarily the existing frame.
Using Inches Instead of Millimetres
Most manufacturers work exclusively in millimetres.
Taking Just One Measurement
Always measure width and height in three places.
Guessing Measurements
Never estimate. Even a small difference can affect the fit.
Forgetting to Measure Twice
Always double-check every measurement before ordering.
Can I Measure Windows Myself?
Yes.
Many homeowners successfully measure their own windows before ordering replacement windows online.
However, if your property has:
- Bay windows
- Unusual shapes
- Older timber frames
- Significant movement in the brickwork
you may prefer to have a professional survey completed for complete peace of mind.
Ordering Made-to-Measure Windows
Once you’ve taken your measurements, you’re ready to choose your new windows.
At Teign Trade Frames, we manufacture high-quality, made-to-measure uPVC windows designed to fit your exact requirements.
Our online ordering system makes it easy to configure:
- Window style
- Size
- Colour
- Glazing
- Hardware
- Decorative options
Every window is manufactured in Devon using quality materials before being delivered nationwide.
Frequently Asked Questions
How do you measure windows for replacement?
Measure both the width and height of the structural opening in three places and use the smallest measurement for each dimension.
Should I measure from the inside or outside?
Where possible, measure from the outside as this provides the most accurate measurement of the opening.
What unit should I use?
Always measure in millimetres (mm).
What if my measurements are different?
Small differences are normal. Always use the smallest measurement when ordering replacement windows.
Can I order made-to-measure windows online?
Yes. Once you’ve confirmed your measurements, you can configure and order made-to-measure windows online through Teign Trade Frames.
Ready to Order Your New Windows?
Now you know how to measure windows, you’re ready to take the next step.
Browse our range of made-to-measure uPVC windows, customise them to your exact requirements and order online with confidence. If you need advice before ordering, our experienced team is always happy to help.
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