Instruction -> Measuring

MEASURING WINDOWS AND DOORS

Standard Windows and Doors

Measure the height of the opening in the brickwork from the outside, and check this dimension at 3 or 4 points across the frame. Using the smallest dimension, deduct 12mm to find the height of the frame you require.
Measure the width of the opening in the brickwork, (ensuring your measuring tape is level) and also check this dimension at 3 or 4 points across the width, and again using the smallest dimension, deduct 12mm to find the frame width you require.
Use this method if using PVC windows.