How the gutter slope calculator works
The rule and its range
1/4 inch of fall per 10 feet toward the downspout — enough to drain, not enough to see. Runs over 40 feet slope from a center high point to downspouts at both ends, halving each side's drop requirement. The calculator flags out-of-range results: under half an inch on this run pools water; over ~2 inches reads visibly crooked and outruns the gutter at the outlet end.
Hanging discipline
Mark the high end one inch below the roof edge, chalk the slope line, and hang to the chalk — eyeballing slope is how flat spots are born. Hidden hangers every 24 inches (snow country) or 36 (standard), screwed into fascia and rafter tails where possible, not just fascia nails.
Seamless and sectional
Seamless aluminum rolls on-site to your run length — one joint at the corners. Sectional gutters assemble in 10-foot sticks with a seam every joint; each seam is a future drip. Seamless costs 20–40% more installed and eliminates most of the maintenance the slope math protects.