im a bit embarassed to ask this question as i should know it, i have two poles both bought second hand.im looking at buying an slx or an extreme but not sure which length. one of my poles reach all 3 storeys and the other reaches all second storey domestic houses, i dont know the length they are
what pole length is for everyday 3rd storey and what length is second storey average properties 
If you have a pole that already reaches the height you want then lay it out on the floor and measure it and you will know exactly what length you require.
When you say 3 storeys do you mean 3 actual storeys (ground, first & second floor) or do you mean 3 storeys above ground floor (actually would be 4 storeys)?
Generally a 22ft pole would reach all two storey houses (ground + first floor) and would also reach low third storey on modern houses. A 25ft pole would however reach nearly all 3rd storey houses even those with slightly set-back 3rd storey dormers.