OK. So carpet is normally sold on a roll 3m (13ft) wide and when you
measure you're rooms you need to remember this. Which means sometimes
you have to buy a bit more because thats the way it comes off the
roll.

What about stair carpet ? OK. My stairs are'nt 13 ft wide but are
quite long. Forgetting about things like patterns, can you measure
your stairs, and divide this into two ?

What I mean is say the 'length' of carpet (inc. up and down bits) is
30ft and the width is, say 5ft. Can't I just buy 15ft of carpet (off
the roll 13ft wide) and split this down the middle leaving two lengths
15ft x 6.5ft ? Then stick it on with a join in the middle of the
stairs ?