Estimate the linear feet of gutter, number of sections, and downspouts needed for your roofline.
This calculator estimates how many linear feet of gutter, how many pre-cut sections, and how many downspouts you'll need to fully gutter a rectangular roofline.
Total Gutter (ft) = 2 × (House Length + House Width). Sections Needed = Total Gutter ÷ Section Length (rounded up). Downspouts = Total Gutter ÷ Downspout Spacing (rounded up, minimum 2).
A house measuring 40 ft × 25 ft has a 130 ft roofline (2 × (40+25)). With 10 ft sections, that's 13 sections, and with downspouts every 35 ft, that's 4 downspouts.
Always round up to the next full section — gutters can be trimmed shorter, but not extended. Add roughly 10% extra material for corners, seams, and waste.
It sums the length of your roofline edges where gutters are needed, then calculates downspout requirements based on roof area and rainfall intensity for proper drainage.
A common rule of thumb is one downspout per 30-40 feet of gutter, or based on roof square footage and local rainfall intensity for more precise sizing.
Yes — steeper roofs shed water faster, which can require larger gutters or more downspouts to handle peak flow during heavy rain.