If you are thinking of getting new blinds, the first thing you will need to do is measure up the area of each window correctly. How you go about doing this will depend greatly on what type of blinds you are planning on purchasing and whether they will be made for you or bought pre-made.
For made to measure blinds, the company that makes them will often send a sales person to your home to make the measurements and talk to you about different options to assist your choice in blinds for example colours, block out blinds and where best to mount them. If this is how you are planning to proceed, you do not really need to do anything other than contact a blind supplier in your area for a quote.
If you are planning however to install your own pre-made blinds determining your measurements properly can be vitally important. The first thing you need to do is determine whether your blinds will be inserted inside or outside of the window casing.
An inside window casing is the most common way of mounting vertical blinds, it means that the full blind will sit inside the window frame, and will not protrude around the edges. This inside mounting is also common for block out or screen blinds, which roll down inside the window frame. In this case measure to the closest half centimetre the inside dimensions from inside the window frame, both vertically and horizontally.
An outside mounting, is where the blinds sit on the outside of the window frame and protrude into the room. This is mostly used for vertical blinds covering patio doors or for roll blinds that you want to sit when closed over the window frame. These tend to block more light as there is no gap between frame and end of the blind. The majority of curtains use an outside mounting.
For an outside mounting you want to measure the area from where you want the blind to start and finish, that is, the total surface area that you want the blind to cover, or measure the window including the frame and then add the number of centimetres to each measurement that you wish to include for overlap on either side, for overhang at the bottom and the distance from the top of the window where the blind will be mounted.
Measure all areas twice to ensure you get it right.