Fitting carpets on stairs is really a job for a professional carpet fitter. They will usually measure free.
If you do it and get it wrong then the carpet will not match as you round corners etc.
In simple terms measure a tread (that's the flat bit) and the rise (that's the bit up to the next stair) and simply multiply by the number of stairs then add 25% to allow for matching where you get joins, round bends etc. Allow for "mini landings" and landings, hallways etc as if they were small rooms. This is where you will need much more carpet than you imagine. You cannot simply buy a length and cut it in half ... it won't work. A professional will be able to judge by experience how much you need dependant on pattern and colour. They will also allow enough to enable the carpet to be moved up or down a few inches every few years to even wear and make your investment last longer. If you DIY then you may come up short and although carpet bought from a single roll will match in colour, if you have to return to the shop for a bit more it may come from a different roll and the colours that look the same in the shop will probably not match when you get them home. It's all to do with dye numbers as in buying wool for home knitting or wall paper (where as you are no doubt aware you need to ensure that each roll of paper has the same "batch code" or colours will vary). Fitting also requires that you take account of the bends etc with an eye to ensuring that the "nap" of the carpet (ie the way the weave runs) is consistent or it will look as if the colours don't match in different light conditions.
Actually buying and fitting carpet through a hallway, up stairs and along a landing is a difficult task and fraught with possible dangers, not only of cocking it up but also of failing to fix it properly and ending up with a nasty fall for somebody.
I am not saying "get a man in" .... I am saying get someone who knows what they are doing in!
As for metres or meters ... Meters are for measuring your electricity, water or gas usage. Metres are measurement but most carpet shops don't know the difference and will prolly have signs that read Meter's
get the shop to measure and fit it is worth it believe me. I have fitted carpets on a DIY basis and it has taken me days to do what a professional can do in a morning. Ultimately you end up with a lot of waste (left over bits) that you have paid for and they have no use. Professional measuring and fitting is worth the little extra cost, most of which you save anyway as they will waste less.
If you are buying a reasonably priced or expensive carpet (and it pays not to stint on stairs) then many shops will fit free.
Alternatively take the route I now take, fit the hall and landings and use a "runner" down the stairs and paint the bits at the side where nobody walks anyway. Very fashionable!
