Measuring windows correctly
Accurate measurements are essential for a perfectly fitting made-to-measure window. This guide explains how to determine the rough opening size correctly — calmly, step by step, with a printable sheet and a photo checklist.
Important: Always give the rough opening size (masonry opening) — not the size of the old window. The window is installed with a small gap (installation joint). Our team checks all measurements before preparing your quote.
Step-by-step measuring
Understanding the rough opening
The rough opening is the opening in the masonry — the distance from masonry edge to masonry edge, without the window frame or plaster. This is the size you enter in the configurator.
Remember: Rough opening = clear width / clear height of the masonry opening.
Measuring the width
Measure the width at three points: top, middle and bottom. Masonry is rarely perfectly straight. Note down the smallest measurement.
- At the top, approx. 10 cm from the upper edge
- At the middle of the opening
- At the bottom, approx. 10 cm from the lower edge
Measuring the height
Measure the height at three points: left, middle and right. Note down the smallest measurement.
Tip: If you are replacing existing windows, measure after the old frame has been removed.
Note down your measurements and enter them in the configurator
Enter the smallest measured size in centimetres in the configurator. Our team checks that everything is plausible and suggests adjustments if needed.
Open the configuratorA4 printable sheet
Klarwerk measuring sheet
Print it once, fill it in right at the opening and transfer the measurements to the configurator later. The sheet itself is in German.
Photo checklist
You can upload photos of the installation site with your enquiry. This helps us check your measurements and assess the installation situation. The following shots are usually sufficient:
Front view
RequiredFull shot of the opening from inside, with the entire window in frame.
Left reveal
Side view from the left, where the wall meets the opening.
Right reveal
Side view from the right, where the wall meets the opening.
Exterior view
The opening from outside — facade, lintel, window sill.
Detail shots
Anything unusual: old window sill, roller shutter box, damage.
Measurements visible
Optional: tape measure in the shot — makes the plausibility check easier.
Photos are no substitute for a technical measurement. They are used solely for our team's plausibility check.
Common measuring mistakes
Common questions about measuring
What exactly is the rough opening?
The rough opening is the clear opening in the masonry — the space the window will later be installed into. Measure without the old frame and without plaster, right at the masonry edge.
What if the old window is still in place?
If possible, measure after the old frame has been removed. If that is not possible, give your best estimate and attach photos. Our team checks your details and gets in touch if anything is unclear.
Why three measuring points per side?
Masonry is rarely perfectly square. Three measuring points cover slight deviations. The smallest measurement governs, so the window is guaranteed to fit.
Which unit should I use for the measurements?
In the Klarwerk configurator, measurements are always entered in centimetres (cm). 180 cm equals 1800 mm.
What is the A4 measuring sheet for?
The measuring sheet is a printable template (in German) on which you can note down all measuring points in a structured way on site. That way you transfer the right values into the configurator later.
Do I need to upload photos right away?
No. Photos are only needed as part of your quote request. The checklist above shows which shots are useful.
What happens if my measurements are unclear?
No problem. After you submit your enquiry, our team reviews your details and contacts you personally if anything is unclear. Nothing goes into production before your measurements are confirmed.
Not sure? No problem. Simply upload photos of the installation site with your enquiry. Our team checks that your measurements are plausible before preparing the quote and gets in touch if anything is unclear.
Ready?
Enter your measurements and get a price
Once your measurements are noted down, transfer them into the configurator. The quote is non-binding, and our team's review is included.