How high do you need to climb?
The top two steps of a ladder should not be used, for safety reasons, so do not choose a ladder that is the exact height or slightly lower than you need.
For step ladders, a rule of thumb is to take the desired height you need to reach and subtract 4 ft.
For extension ladders, a rule of thumb is to take the height of the roof line/eaves and add 7’. This will account for overlap within the ladder and allow for enough length to safely get off the top of the ladder