Roof pitch calculator
Pitch is how steep the roof is, usually said like 6/12 — six inches of rise for every twelve inches of horizontal run. From that ratio you also get degrees and a slope factor that turns a flat footprint into the actual surface area you cover with shingles. Enter rise and run. This page will not walk your ridge with a harness or price a tear-off. For shingle bundles you will still need area × pitch factor × waste on a later roofing page.
Geometry only — not a roofing quote or shingle order.
When to use
Checking existing pitch before buying a ladder bracket; converting a drawing’s angle to X/12; getting a multiplier for a rough material area from a rectangular footprint.
When not to
Multi-level roofs with hips, valleys, and dormers — break into planes or hire a takeoff. Structural rafter sizing (birdsmouth, snow load) is engineering, not this form.
Assumptions
Single plane ratio; run > 0; pitch displayed as rise-per-12. Slope factor = sqrt(1 + (rise/run)²). No hip/valley length module in batch 1.
Worked examples
Example 1
Rise 6 in over run 12 in
→ 6/12 pitch, ≈ 26.6°, factor ≈ 1.118
A 1,000 sq ft footprint ≈ 1,118 sq ft of surface before waste.
Example 2
Rise/run that equals about 30°
→ Pitch ≈ 6.93/12, factor ≈ 1.155
Rounding pitch to a common carpenter fraction (7/12) is a field choice.
How it calculates
Enter rise and run in matching units; read X/12, degrees, and slope factor. Optional footprint × factor ≈ surface.
- Measure rise over a known run (often 12 inches).
- Enter both numbers in the same unit.
- Optionally add footprint area for a surface estimate before waste.
pitch_on_12 = (rise / run) × 12 degrees = arctan(rise / run) × 180/π slope_factor = sqrt(1 + (rise/run)²) roof_surface ≈ footprint_area × slope_factor
Common traps
- Rise/run units must match. Mixing feet of run with inches of rise without converting will invent a ski-jump.
- Pitch vs slope slang. Some folks say “slope” for percent grade; we show X/12, degrees, and factor explicitly.
- Footprint ≠ shingle order. Still add waste for starter, ridge, and cuts.
- Low-slope membranes are a different product world below certain pitches.
Next tool
Material quantity for pads and grounds → concrete calculator / gravel calculator.
Exterior walls → paint calculator.
FAQ
Level a 12-inch run along a rafter or board, measure vertical rise in inches — that rise is the X in X/12.
Related
Estimate only — not a contractor bid or engineered takeoff. Confirm bag yields and local codes before you pour or order.