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Roof Slope Calculator

Convert roof slope between degrees, percent, and rise-in-12.

Pitch from rise / run
Optional — footprint area

What is roof slope calculator?

Roof slope is the steepness of a roof, the same quantity that carpenters call pitch. In engineering, code, and solar-panel contexts the slope is usually quoted in degrees or percent grade rather than the rise-in-12 ratio you see on shingle wrappers. They’re all the same math under the hood.

This calculator takes rise and run in any matching unit and converts to degrees, percent grade, X:12 pitch, and slope factor in one shot. Add an optional length × width footprint to see the actual roof surface area for that slope — the number you need when sizing shingles, metal panels, or membrane.

Low-slope roofs need careful drainage planning: most codes require at least 1/4 inch per foot (about 2%, 1.2°) of slope to avoid ponding water. Steep-slope roofs (above 9:12, ~37°) trigger fall-protection requirements and usually have separate shingle warranty terms.

When to use a roof slope calculator

  • Gutter sizing — Gutter manufacturers reference slope in percent or inches-per-foot — convert from a known pitch quickly.
  • Solar-panel angle planning — Solar arrays are quoted in degrees of tilt. Convert an existing roof pitch into degrees to check the panel's optimal angle window.
  • Drainage and code — Confirm a roof slope meets the minimum drainage code (typically 1/4 inch per foot for low-slope built-up roofs).

How to use the Roof Slope Calculator

  1. Measure rise and run — Rise is vertical, run is horizontal. Any equal units work — inches and inches, feet and feet, etc.
  2. Read slope in your preferred format — Output shows degrees, percent grade, pitch (X:12), and slope factor side by side.
  3. (Optional) compute roof area — Fill in the footprint to get the actual roof surface area for that slope.

Worked examples

Standard 6:12 pitch

Input:  Rise=6, Run=12
Output: 26.57° — 50.0% — 6.00:12

Low-slope 1/4-inch-per-foot drainage

Input:  Rise=0.25, Run=12
Output: 1.19° — 2.1% — 0.25:12

Solar-friendly 35° tilt

Input:  Rise=8.4, Run=12
Output: 35.00° — 70.0% — 8.40:12 — slope factor 1.221

Frequently asked questions

What's the difference between slope and pitch?
In residential roofing they mean the same thing — the steepness of the roof. Slope is more often quoted in degrees or percent (engineering / solar contexts); pitch is more often quoted as X:12 (carpentry / shingles).
What's the minimum slope for asphalt shingles?
About 9.5° (2:12 pitch) per most manufacturers, with special underlayment below ~18° (4:12). Always check the product's specific warranty.
How do I convert slope percent to degrees?
Degrees = atan(percent / 100) × 180/π. A 50% slope is atan(0.5) ≈ 26.57°.
Why do solar installers quote tilt in degrees?
Solar yield depends on the angle of incidence with the sun. Degrees normalize across all roof shapes and let installers map tilt to latitude / season tables directly.
What slope is required for a flat / built-up roof?
Most codes require at least 1/4 inch per foot of slope (about 2%, 1.2°) on 'flat' roofs to drain water properly. Below that, ponding is a structural and warranty concern.
Can a roof be too steep?
Above ~12:12 (45°) is structurally fine but requires fall arrest, costlier labor, and specialty fasteners. Many shingle warranties have a separate spec for steep-slope (above 21:12, ~60°).
How does slope affect material cost?
Material scales with the slope factor — the multiplier from horizontal footprint to actual roof surface. A 12:12 needs ~1.414× the material of a flat roof for the same footprint.

Roof Pitch Calculator

Convert rise and run into the four standard pitch formats.

Roof Truss Calculator

Compute rafter length, peak rise, and chord length from span and pitch.

Roof Cost Calculator

Estimate total roof material cost — shingle or metal — from one form.