An easy guide in five quick steps. How to measure up for your new garage door from Arridge Garage Doors. All you need is a tape measure. This is a quick step by step guide on how to get the correct size garage door to suit your garage opening. Detailed explanation on what is the garage brick to brick width, garage side room and garage opening headroom and the easy way to measure these important dimensions before choosing the correct garage door for your garage opening sizes.