DIY Instructions

How to Measure

It’s straightforward to measure your windows for glass blocks. All measurements must be taken from outside the property, double brick, brick veneer, stone, or Hebel etc. To get the best idea of measurements possible, as not all windows are square. We need to take 3 measurements for height and 3 for the width from all in millimetres. Please see the illustration below.

It’s best to print out and carry the instructions with you when measuring. You can find a measuring worksheet included in each printout. To get the printable pdf version, simply click the red printer icon when browsing your product below.


  1. Always use a metal tape measure, a cloth tape measure will not be accurate
  2. We require all of your measurements in millimetres
  3. Do not round your measurements, we require the measurements to the exact millimetre (mm)
  4. Measure width then drop in this order, try not to get these mixed up
  5. Measure every window, there might be slight variations even if they are duplicate windows, and this could affect your window fitting perfectly
  6. Do not take your measurements from house plans as they are not accurate
  7. If measuring with a partner, make sure the measurements are repeated out loud as they are written down
  8. Double and triple check all details are correct before ordering, and remember not to deduct anything off any Recess Fit measurements as our factory will do this to ensure a perfect fit
Recess (outside Fit) Glass Block Window
  1. Measure the width in mm on the outside of the window frame from left side to right side in three places (Top, Centre, and Bottom) and use the smallest of the three measurements.
  2. Measure the drop in mm from the top of the inside recess to the base of the inside sill in three places (Left, Centre, Right) and use the smallest of the three measurements.
  3. If you have a brick seal, measure the thickness as this may need to be taken out.


If you have further questions, our friendly customer service team are available over the phone on 08 7082 0453, email at