Use measurements from plans or a safe method. Pitch geometry does not establish safe access, product approval, drainage design, snow or wind capacity, framing adequacy, or code compliance.
01 / Formula
How this is calculated
Pitch per 12 = rise ÷ run × 12; angle = arctan(rise ÷ run); factor = √(run² + rise²) ÷ run02 / Assumptions
What the estimate assumes
- ✓Rise and run use the same units.
- ✓Run is horizontal, not along the roof surface.
- ✓The measured slope is planar and consistent.
03 / Worked example
See the math in context
A 6-in rise over 12-in run is 6:12, approximately 26.57°, with a 1.118 area factor.
04 / Guidance
Do not estimate pitch from appearance
Perspective can be misleading. Use construction documents, a qualified measurement service, or an appropriate remote measurement method.
05 / Guidance
Check product slope limits
Roof coverings and underlayments have minimum slopes and may require special details at lower slopes. Use the current instructions for the exact assembly.
Questions
Frequently asked
Can I measure or inspect a roof by walking on it?+
Do not access a roof without appropriate training, equipment, conditions, and fall protection. Use plans, ground measurements, aerial reports, or a qualified roofing professional when direct access is unsafe.
Does this calculator approve a roofing system?+
No. Verify deck condition, slope limits, underlayment, ice-barrier, flashing, ventilation, fasteners, wind requirements, fire classification, local code, and the exact manufacturer instructions.
What should be measured separately?+
Break out each roof plane plus valleys, hips, ridges, eaves, rakes, walls, penetrations, dormers, low-slope transitions, and special membranes. Geometry alone does not create a complete roofing order.
Sources