Calculate gutter length, downspouts, hangers, end caps, and connectors needed for your roof.
Step 1: Measure the total length of roof edge that needs gutters.
Step 2: Enter the number of gutter runs (separate straight sections).
Step 3: Set the downspout spacing. Standard is 40 ft (12 m) maximum between downspouts.
Step 4: Enter the number of corners (inside or outside) where gutters change direction.
Hangers are calculated at 24" (600 mm) spacing for secure mounting.
Downspouts should be spaced no more than 40 feet (12 m) apart. For areas with heavy rainfall, consider spacing them 20–30 feet (6–9 m) apart.
5-inch (125 mm) K-style gutters are the most common residential size. For larger roofs or heavy rainfall areas, 6-inch (150 mm) gutters with 3×4" downspouts are recommended.
Gutter hangers should be spaced every 24 inches (600 mm) for standard conditions. In areas with ice/snow loads, spacing of 18 inches (450 mm) is recommended.
As a guide, one downpipe per 10–12 m of gutter, or for every 50–60 m² of roof drained. The calculator suggests a sensible number.
A slight fall of about 3 mm per metre towards the downpipe lets water drain without pooling or overflowing.
