How to measure your room for a timber floor? If your room is a simple shape like a rectangle or a square to find out how much timber is needed multiply the length by the width. This will give you the total area needed. When the rooms is a little more complex with windows and complex areas. Divide your room into two smaller areas. Call one are A and the other area B. As above find out the area of A and the area of B and add them together. The final step is to add a waste factor. We suggest 10% waste. This will account for any off cuts that are needed. It is best to have a little left over at the end of a job as apposed to having too little timber flooring.