Roof Pitch Multipliers & Formulas Reference
Comprehensive trigonometry tables, slope factors, hip/valley multipliers, and construction glossary for professional estimators and builders.
Master Pitch Multiplier Reference Table (1/12 to 24/12)
Common rafter slope multipliers and 45° diagonal hip/valley multipliers.
| Pitch (Rise/12) | Slope Angle | Slope Multiplier | Hip/Valley Factor | Classification |
|---|---|---|---|---|
| 0/12 | 0.00° | 1.0000 | 1.4140 | Low Slope (Membrane/Double Felt) |
| 1/12 | 4.76° | 1.0030 | 1.4160 | Low Slope (Membrane/Double Felt) |
| 2/12 | 9.46° | 1.0140 | 1.4240 | Low Slope (Membrane/Double Felt) |
| 3/12 | 14.04° | 1.0310 | 1.4360 | Low Slope (Membrane/Double Felt) |
| 4/12 | 18.43° | 1.0540 | 1.4530 | Conventional (Walkable) |
| 5/12 | 22.62° | 1.0830 | 1.4740 | Conventional (Walkable) |
| 6/12 | 26.57° | 1.1180 | 1.5000 | Conventional (Walkable) |
| 7/12 | 30.26° | 1.1580 | 1.5300 | Conventional (Walkable) |
| 8/12 | 33.69° | 1.2020 | 1.5630 | Moderately Steep (+15% labor) |
| 9/12 | 36.87° | 1.2500 | 1.6010 | Moderately Steep (+15% labor) |
| 10/12 | 39.81° | 1.3020 | 1.6410 | Steep / Mansard (+25% labor) |
| 11/12 | 42.51° | 1.3570 | 1.6850 | Steep / Mansard (+25% labor) |
| 12/12 | 45.00° | 1.4140 | 1.7320 | Steep / Mansard (+25% labor) |
| 14/12 | 49.40° | 1.5370 | 1.8340 | Steep / Mansard (+25% labor) |
| 16/12 | 53.13° | 1.6670 | 1.9440 | Steep / Mansard (+25% labor) |
| 18/12 | 56.31° | 1.8030 | 2.0620 | Steep / Mansard (+25% labor) |
| 20/12 | 59.04° | 1.9440 | 2.1860 | Steep / Mansard (+25% labor) |
| 24/12 | 63.43° | 2.2360 | 2.4490 | Steep / Mansard (+25% labor) |
Glossary of Roofing Terms
Standard definitions used in building codes, architecture plans, and manufacturer warranties.
Square (SQ)
A standard roofing unit equal to 100 square feet (9.29 m²) of roof surface.
Pitch / Slope
The incline of a roof expressed as the vertical rise in inches per 12 inches of horizontal run (e.g. 6/12).
Eave
The lower horizontal edge of a roof that overhangs the exterior wall, where gutters are installed.
Rake
The inclined, sloping edge of a gable roof plane leading up from the eave to the ridge.
Ridge
The highest horizontal line formed by the junction of two sloping roof planes.
Valley
The internal angle formed by the intersection of two sloping roof planes that channels rainwater down.
Hip
The inclined external angle formed by the meeting of two adjacent sloping roof planes.
Starter Strip
The initial row of specialized adhesive-backed shingles installed along eaves and rakes to prevent wind blow-off.
Underlayment
Water-resistant barrier installed directly onto the roof deck beneath the shingles (synthetic or asphalt-saturated felt).
Ice & Water Shield
Self-adhering modified bitumen waterproof membrane required along eaves and valleys to prevent leaks from ice dams.
Drip Edge
Non-corrosive metal flashing installed along roof perimeters to guide runoff cleanly into gutters.
Flashing
Sheet metal components installed at roof joints, chimneys, walls, and skylights to prevent water penetration.