I'm not sure what length of ladder mine is, but it's a double extention with 13 rungs on each section. They could reach 99% of 1st floor windows on my round; prior to WFP.
Make sure they're not B & Q ladders and they conform to BS EN131 certified safety standard. (They will have yellow feet and have this safety marking on the side).
I've fallen from a dodgy set of B & Q ladders. They may be lighter, but they 'curve' after a short while and just aren't safe.
I'd also recommend that you don't do any 2nd floor work from ladders; wait till you get a WFP.
When you purchase your ladders, buy some spare feet and change them when they're worn. Don't be one of these window cleaners who use ladders with no feet; worn away to the bare alluminium.
Also a Rojak Ladder Stopper and ladder matts are great too, for use on uneven or dangerous surfaces.
Also, tell any potential customers at the quoting stage what windows you CAN'T do; as many properties will have windows that are dangerous to get access to (such as ones above porches).
When I first started I did them all; no matter how dangerous they were; regularly I'd be clinging onto a window sill with one hand, on top of a steeply pitched roof and sqeeging with my other hand; 'cos I'm a (thick) Geordie!!!
It took a fall to thump some sense into me.