That translates into one centimeter of depth for every 3 or 5 meters of depth. The standard slope of rain gutters is half an inch per 10 feet. This means that your gutter should be half an inch lower in height every 10 feet until it reaches the downspout. In the case of gutters that extend more than 40 feet, it is advisable to have a downspout at each end and start at the highest point of the gutter, in the center.
However, rain gutters that reach distances shorter than 40 feet don't require two different slopes. In these cases, the slope is thin and drives the excess water into one direction.
