Why slope matters
Gutters work because water flows downhill. The slope just has to be enough to overcome friction, debris drag, and the surface tension keeping a puddle stuck in the trough.
About 1/16 inch of fall per foot of run is the practical minimum - below that, water sits and breeds mosquitoes, mold, and rust. 1/4 inch per foot is the practical maximum before the gutter looks tilted from the street.
total_drop = run_length × slope_per_foot
Frequently asked
What slope is the most common?
1/8 inch per foot - about 1% grade. It’s enough fall to drain reliably without making the gutter look out of square with the fascia.
Center high point or end-to-end?
For runs over 40 feet, almost always center high. It cuts the maximum drop in half, splits flow between two downspouts, and keeps both ends close to the fascia line.
Why not just install flat gutters?
You can - and many modern systems sell themselves as “level” - but standing water still finds the low spot from house settling, debris, or ice. A small pitch is cheap insurance.