Depending on the Retract-A-Gate model you intend to or have already purchased (either 52" or 72"), your gate will fit openings UP TO a maximum of 132 cm or 172 cm. These maximums are the total distance (gate and brackets) that the baby gate can cover.

The height of the mesh on the retractable baby gate is about 87.5 cm and the total height to the top of the lock is just under 96 cm. You would need to ensure there are enough clearance space where the gate is going to be installed so that you can not only install the gate but also have easy access to the childlock mechanism. The gate also needs to sit on a flat surface for proper operation. 

Next, you need to decide on where to install the wall brackets. These are Universal Brackets which means that all the brackets are identical. The brackets on each side are mounted at about 8cm and 78.5 cm off the floor and require about 6.5 cm wide flat surface to attach to (see the size of brackets in images above). Unlike most gates, there is some leeway to the height for where the brackets are mounted, especially on the reel side that holds the safety gate. This makes the installation easier. 

When completely retracted, Retract-A-Gate only protrudes less than 9 cm from the wall. This makes it fairly flexible where you choose to install your wall brackets without the need to worry about the gate blocking the way. For example, for a typical doorway, you can choose to install directly within the doorway, or, in the event, you don't have the 6.5 cm necessary to mount your Universal Brackets in the doorway, the brackets can also mount around the corner of the doorway, either on the door molding or on the wall as long as you do not exceed the maximum distance it can cover.

If there are baseboards/skirtings where you will be installing your Retract-A-Gate, you need to measure the height and thickness of your baseboard/skirtings to determine if you will need wall spacers and how many you would need. For more information on when Spacers would be necessary and useful, check out "FAQ: Do I need spacers?".