Gutter Calculator
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What Your Result Means
- Recommended Size: Either 5" or 6" K-style gutter. Heavier rainfall or steeper pitches require larger gutters to handle more water volume per minute.
- Downspouts: The number of 3" or 4" downspouts you need spaced along your roofline. More downspouts = faster water drainage and lower risk of overflow.
- Total Linear Feet: The combined length of gutter you'll install (roof length × 2 for both sides of the peak). Use this to order materials and estimate labor.
- Estimated Cost: A material-only range based on aluminum seamless gutter. Actual price varies by region, installation complexity, and local labor rates.
How This Calculator Works
You enter your roof length, pitch angle, and local rainfall rate. The tool applies NFPA drainage formulas to size gutters and determines downspout spacing. A steeper roof or heavier rain concentrates runoff, requiring bigger gutters (6" instead of 5"). Downspouts are spaced closer on high-rain roofs (20 ft apart) and farther on light-rain roofs (30 ft apart). The cost is computed from typical aluminum gutter pricing ($5–$10 per linear foot).
Quick Questions
What's the difference between 5" and 6" gutters?
A 6" gutter holds about 26% more water volume than a 5" gutter. It's needed in heavy-rain or steep-roof areas to prevent overflow during storms. 5" is standard for most climates.
How do I know my roof pitch?
Pitch is the slope ratio (rise ÷ run). A 6:12 pitch means the roof rises 6 inches for every 12 inches of horizontal distance. You can estimate by looking at your roof angle, or measure it with a level and ruler. Your roof inspector or home survey may also list it.
Can I space downspouts farther apart to save money?
You can, but closer spacing is safer and reduces overflow risk during heavy rain. If you use wider spacing, monitor the gutter after storms. Local building codes may also specify minimum downspout frequency.
What's included in the cost estimate?
The estimate covers gutter material and basic downspout costs. It does not include labor, hangers, fascia boards, or soil drainage systems. Get local quotes from contractors for a true project cost.
Do I need gutter guards?
Gutter guards reduce leaf buildup and maintenance but add $3–$5 per linear foot. They're recommended in areas with heavy tree coverage or where you want minimal cleaning. Calculate the cost separately.
Sources
- National Fire Protection Association (NFPA) (Water drainage and gutter sizing standards)
- HomeAdvisor (Gutter material pricing and regional cost data)
- American Society of Plumbing Engineers (ASPE) (Roof drainage formulas and downspout design)
- The Old Farmer's Almanac (Regional rainfall intensity data)
Method & review
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.