Accurate measuring is the most important step when buying window blinds on the net. It is for this reason that it is also the step that causes the most anxiety. --- RELAX --- if you can read a ruler and you follow the instructions below - you'll do alright.
Note: Your blinds are made to the specifications you provide. If you make a mistake here there is no refund or return policy to protect you. If the blind is made too large it can be cut down for you for a fee. If the blind is too small you will need to order a new blind. So accuracy and precision is a must.