Measure the opening where your secondary glazing will be fitted. Always take three measurements across the width and three measurements across the height.
Measure horizontally from reveal to reveal at the top, middle and bottom of the opening.
Measure vertically from reveal to reveal at the left, centre and right of the opening.
Enter your smallest measured width and height as a Tight Recess Size and we'll deduct 6mm for fitting — or, if you've already allowed for fitting tolerance yourself, enter the finished dimensions as an Exact Size.
Our estimator allows you to select equal splits, so you only need to measure the split position if your existing window has unequal splits that you want the secondary glazing to follow.
Measure vertically from reveal to the centre of the existing horizontal bar.
Measure horizontally from reveal to the centre of the existing vertical bar.
Bays need one extra step — decide where your secondary glazing will sit, then measure each section along that line.
Choose where your secondary glazing will sit within the bay, allowing for the frame depth you have selected, then measure each section along this line from corner to corner. These are your Tight Recess Sizes — enter them as measured and we'll deduct 6mm for fitting, or enter Exact Sizes if you've already allowed your own tolerance.
