How do you measure an area for hardwood floors?
To measure how much flooring you will need for any room you 
must start off with using a tape measure.
To simplify, you will need the length times the width of any room which will give you the surface area. (L x W = A²)
This is generally measured in meters so the total will be m².
Start by finding the longest length of the room and measure from one wall to the other. Repeat this with the other walls.
What about if there are obstacles in the way?
In terms of awkward shapes and obstacles like bay windows and chimney breasts etc, these can be overcome in two ways. 
The first by simply measuring them separately and deducting it off the total surface area. Or generally, what’s done is they are measured as if the room had completely straight sides with no obstacles in the way (areas highlighted in red in the image shown). This area will then be an addition to the 5-10% waste/cuts required. Even when measuring accurately the 5-10% extra is still required.
What if I have joining rooms?
The easiest way to achieve the total area required for the hardwood floor if you have conjoining rooms is
to separate each area room individually, including any hallways. Find the most square of all the rooms, and repeat the process above for each area.