It is tempting to assume bigger gutters are simply better, but sizing a gutter system correctly takes more than picking the larger option.
What Actually Determines Gutter Size
We factor in your roof's square footage, its pitch, the type of roofing material, the number and placement of downspouts, and local rain intensity data from NOAA. We run these numbers through the SMACNA gutter and downspout sizing calculator rather than eyeballing it.
When 5 Inch Gutters Make Sense
Five inch K-style gutters are sufficient for the large majority of homes in Idaho. If your roof is a standard residential size with a typical pitch, 5 inch gutters will almost certainly handle the water volume without issue.
When 6 Inch Gutters Make Sense
Larger roofs, steeper pitches, metal roofing (which sheds water faster than shingles), and commercial buildings often call for 6 inch gutters or box gutters. If your current 5 inch system overflows during heavy storms, upsizing is usually the right call rather than just adding more downspouts.
The bottom line: the right size depends on your specific roof, not a general rule of thumb. That is exactly why we measure every job rather than quoting sight unseen.
Ben Beers
Ben founded Idaho Seamless Gutter out of a shop in Greenleaf, Idaho in 2017 after years of experience in roofing and remodeling. He still runs estimates and installs alongside the crew.
