What is the difference between slope and pitch?

Slope percentage is rise divided by run as a percentage — a 6/12 roof is a 50% slope. Pitch is the rise-over-12 ratio itself. They describe the same geometry in different units.

What is the minimum slope for a roof?

It depends on the covering: 2/12 for asphalt shingles, 3/12 for exposed-fastener metal and wood, 2½/12 for tile, and as low as a quarter inch per foot for sealed single-ply membrane. Below the minimum no manufacturer will warrant the material.

What slope is a quarter inch per foot?

About 2.08%, or a 0.25/12 pitch. It is the minimum fall required on a low-slope roof so water drains rather than ponds.

Can a roof be completely flat?

It should not be. Codes require a minimum fall so water drains. A genuinely level roof ponds, and standing water shortens the life of any membrane sharply.

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We build free, accurate construction calculators for homeowners and contractors. This article is part of our roofing knowledge base — we also publish guides and tools for other home improvement projects:

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Measuring on the roof rather than from the attic? A roof pitch finder reads the slope straight off the shingles.

Every pitch from 1/12 to 24/12 in degrees, percent and multiplier is on the roof pitch chart.

Last updated: April 24, 2026 · Reviewed by the Smart Roofing Calculator editorial team