Gutter Size Calculator
Determine the correct gutter size, number of downspouts, and total material footage for your home. This calculator uses roof drainage area and local rainfall intensity to recommend proper gutter and downspout sizing per industry standards.
Roof & Gutter Details
Full Breakdown
Adjusted Roof Area
Drainage per Side
Recommended Gutter Size
Total Gutter Length
Downspouts Needed
Inside Corners
End Caps
Hangers (every 3 ft)
Estimated Cost
How to Use This Calculator
- Enter the roof eave length and rafter run (horizontal distance from eave to ridge).
- Select your roof pitch factor and local rainfall intensity.
- Choose how many sides have gutters (most gable roofs = 2).
- Optionally enter a price per foot for cost estimates.
- Click "Calculate Gutters" for sizing and material counts.
The Formula
Adjusted Roof Area = Eave Length × Rafter Run × Pitch Factor
Drainage Area per Side = Total Area ÷ Sides
Gutter Size: 5″ K-style handles up to 5,520 sq ft at 6 in/hr; 6″ handles up to 7,960 sq ft
Downspouts: 1 per 20 linear feet of gutter (2×3″) or 1 per 30 ft (3×4″)
Hangers: 1 every 3 feet
Drainage Area per Side = Total Area ÷ Sides
Gutter Size: 5″ K-style handles up to 5,520 sq ft at 6 in/hr; 6″ handles up to 7,960 sq ft
Downspouts: 1 per 20 linear feet of gutter (2×3″) or 1 per 30 ft (3×4″)
Hangers: 1 every 3 feet
Sizing is based on SMACNA (Sheet Metal and Air Conditioning Contractors' National Association) standards. 5″ K-style gutters with 2×3″ downspouts are the most common residential size.