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25 calculators

Gutters & Drainage Calculators

Size gutters, downspouts, and drainage systems for your roof. All tools are free — no registration or download required.

Gutter Size Calculator

Calculate the correct gutter size based on roof area and rainfall intensity

Downspout Calculator

Calculate number and size of downspouts needed for your gutter system

Gutter Cost Calculator

Estimate gutter installation costs by material type and linear footage

Gutter Extension Calculator

Calculate downspout extension length to direct water 6ft+ from foundation — splash blocks vs buried pipe vs roll-up extensions

Flat Roof Drain Sizing Calculator

Size internal roof drains by IPC code — Q = area × rainfall / 96.23 GPM, primary + overflow drain count

Gutter Run Length Calculator

Calculate maximum gutter run between downspouts by gutter size, rainfall intensity, and drainage area — plus expansion joint count

Roof Gutter Pitch per Foot Calculator

Standard gutter pitch 1/16" per foot toward downspout. Total drop, high-end height, and level-to-drop marking schedule for single or center-downspout gutter runs.

Roof Storm Water Harvesting Calculator

Capturable rainwater: catchment_area × rainfall × 0.85 efficiency × 0.623 gal/sqft/in. Annual gallons, tank size for X days storage.

Rainwater Collection Calculator

Calculate rainwater harvest potential from your roof area

Downspout Placement Calculator

Calculate optimal number and position of downspouts based on roof area, rainfall intensity, and gutter capacity

Gutter Hanger Spacing Calculator

Calculate number of hangers and optimal spacing — 18 inches for snow regions, 36 inches for mild climates

Leaf Guard Linear Feet Calculator

Estimate total linear feet of gutter guard needed based on roof perimeter and gutter layout with cost estimate

Rain Chain Calculator

Calculate rain chain length, cup count, flow capacity, and number of chains needed based on roof area and rainfall

Stormwater Runoff Calculator

Rational method Q = C×i×A: runoff coefficient by material (metal 0.95, shingle 0.90, tile 0.85, green roof 0.35) × rainfall intensity × area in acres — output in CFS and GPM

Dry Well Sizing Calculator

Size a dry well using volume = roof area × rainfall × 0.623 × runoff coefficient / 7.48 — outputs required cubic feet, well depth, gravel fill, and overflow pipe recommendation

Rain Garden Sizing Calculator

Size a rain garden at 20–30% of contributing roof area — soil-adjusted depth factor, ponding depth, garden dimensions (2:1 ratio), soil amendment depth, and plant count

Roof Parapet Scupper Calculator

Scupper sizing through parapet walls: width = sqrt(Q/3.0), height = width × 0.67. Emergency overflow scuppers = primary × 1.5. IBC 1503.4 compliance.

Hip Roof Water Shed Calculator

4-direction drainage for hip roofs. Each face catchment percentage of total. GPM per face and gutter sizing vs single perimeter system.

Gutter Slope Calculator

Calculate the correct slope/grade for gutter installation

Roof Drainage Calculator

Calculate drainage requirements for flat and low-slope commercial roofs

Gutter Guard Calculator

Calculate gutter guard materials needed and compare costs by type

Scupper Drain Sizing Calculator

Calculate required scupper width and height based on roof drainage area and rainfall rate per IPC code

Box Gutter Calculator

Calculate internal box gutter width, depth, and outlet sizing based on roof catchment area and SMACNA rainfall standards

Hidden Gutter Calculator

Calculate concealed/built-in gutter dimensions, liner area, and outlet sizing for architectural applications

French Drain Calculator

Calculate french drain dimensions for foundation drainage from roof runoff

About Gutters & Drainage

This category contains 25 specialized calculators covering all aspects of gutters & drainage. Whether you are a homeowner planning a project or a roofing contractor estimating materials, these tools give you accurate results based on industry-standard formulas.

Each calculator includes step-by-step guidance, example calculations, and explanations of the underlying formulas so you understand exactly how your numbers are derived. Results are suitable for budgeting and planning — always consult a licensed roofing professional before starting structural work.

How to Use These Calculators

Start by entering your roof's basic dimensions. Most calculators need length, width, and pitch at minimum. Results update instantly as you type. Use the unit toggle to switch between imperial (feet, inches) and metric (meters) measurements. All calculators are mobile-friendly and work on any device.

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