The first thing to do when measuring for areas of carpet or flooring is to draw out on a piece of graph paper a plan of all the perspective areas you are going to carpet. leave the measurements at the moment this will come later. just map out the areas roughly to the shape they are it does not have to be too in depth just a rough shape will be fine if you have stairs draw them as a long rectangular shape and write how many stairs make sure you draw the rooms and the stairs like a plan so it looks like a bird's eye view
When you have your floor plan start to take all the measurements, remember when measuring check that you have allowed for all the widest points. Have an idea of which way the carpet or flooring will run and where you may have to put joins, if joins are necessary to plan them to go in parts of the room where there is not much traffic, try not to put them right in the middle of a doorway. Always make sure all your carpet goes the same way especially if it has a weave
Please be very careful when working out how much carpet you will need if unsure call a carpet installer as this will save you money. you now have your floor plan start to calculate what sizes of carpet you will need do not order by square meter this does not work always order by lengths you should by now know the width of your material take this into account