A 4/12 roof pitch equals 18.43 degrees with a slope factor (multiplier) of 1.054. A 6/12 pitch equals 26.57 degrees with a multiplier of 1.118. A 12/12 pitch is exactly 45 degrees. This roof pitch calculator converts between all three formats instantly and covers every pitch from 1/12 to 12/12.

Roof pitch notation is simple: X/12 means the roof rises X inches for every 12 inches of horizontal run. 4/12, 4:12, and "4 in 12" all describe the identical slope. Below you'll find three calculator modes: Pitch Calculator (convert between pitch ratio, degrees, and slope %), Ridge Height (enter span and pitch to find ridge height), and Roof Area (enter footprint and pitch to find actual roof surface area).

Further down this page you'll find the complete pitch-to-degrees conversion table (1/12 through 12/12, all values verified) and a minimum pitch guide covering asphalt shingles, metal roofing, shed roofs, and snow-country recommendations. Use the calculator above or the complete pitch chart below.

Roof pitch chart — all pitches 1/12 to 12/12 in degrees, slope, and multiplier

4/12 = 18.43°  |  5/12 = 22.62°  |  6/12 = 26.57°  |  8/12 = 33.69°  |  12/12 = 45.00°

The table below converts every standard roof pitch from 1/12 to 12/12 into degrees, slope percentage, the multiplier (slope factor), and the rise per foot of run. This is the complete roof pitch chart for residential and light commercial roofing.

Degrees = atan(rise÷12) × (180÷π). Multiplier = √(rise² + 144) ÷ 12. All values verified: 4/12 → atan(4/12)×57.296=18.435° ✔, multiplier √160÷12=1.054 ✔. 6/12 → atan(6/12)×57.296=26.565° ✔, multiplier √180÷12=1.118 ✔. 12/12 → 45.000° exact ✔, multiplier √288÷12=1.414 ✔.

The slope factor (multiplier) tells you how much larger the actual roof surface is than the horizontal footprint. A 6/12 pitch has a multiplier of 1.118, meaning a house with a 2,000 sq ft footprint actually has 2,236 sq ft of roof surface (2,000 × 1.118). This matters when calculating roofing materials — always calculate shingles and underlayment from the actual roof area, not the footprint.

Pitch vs slope

Pitch and slope mean the same thing when describing residential roofs. Pitch is expressed as a ratio (4/12), slope as a percentage (33.3%), and the angle as degrees (18.43°). All three describe the same steepness.

How to calculate roof pitch — three methods

Method 1 — Measuring on the roof surface

Use a spirit level (12 inches long) and a tape measure. Hold the level horizontally on the roof surface. Measure 12 inches along the level from the roof surface to the end of the level (this is your run = 12"). Now measure vertically from the roof surface up to the end of the level (this is your rise in inches). Your pitch is rise/12. A roof slope gauge tool (also called a pitch gauge or digital angle finder) makes this even faster — place it on the roof surface and read the angle directly.

Method 2 — Measuring from the attic

Stand in the attic. Hold a level against a rafter, horizontally. Measure 12 inches along the rafter from one end. Measure vertically from the 12-inch mark to the bottom of the rafter. This gives you the rise per 12 inches of run.

Method 3 — Calculating from known dimensions

If you know the ridge height and building span: pitch = (ridge height ÷ half-span) × 12. For a 24 ft wide building with a 6 ft ridge: pitch = (6 ÷ 12) × 12 = 6/12.

Minimum roof pitch by roofing material — and what pitch for snow

Minimum pitch for asphalt shingles: 2/12 (with double underlayment) — standard installation requires 4/12 or steeper.
Minimum pitch for metal roof (standing seam): 0.25/12 (essentially flat — designed for low slope).
Minimum pitch for metal roof (corrugated/exposed fastener): 3/12 recommended.
Minimum pitch for clay/concrete tile: 4/12.
Minimum pitch for wood shake: 3/12.
Minimum pitch for EPDM/membrane: 1/4:12 (flat roof category).

Minimum pitch for metal roof (expanded)

Standing seam metal roofing is the best choice for low-slope applications — it can be installed at pitches as low as 0.25:12 (a quarter inch of rise per foot of run). Corrugated metal panels with exposed fasteners require a minimum of 3/12 to prevent water from backing up under the overlaps. If you're planning a metal roof at low slope, always use standing seam — not corrugated.

Roof pitch for snow

In regions with heavy snowfall (New England, Upper Midwest, Mountain West), the recommended minimum pitch is 6/12 or steeper. Steep pitches allow snow to slide off rather than accumulate — snow accumulation creates structural load that can cause roof failure. Metal roofing on steep pitches (6/12+) is particularly effective in snow country because snow slides freely. For flat or low-slope roofs in snow regions, structural engineering for snow load is required.

Common roof pitches by application — shed, porch, hip roof guide

Shed roof pitch

The minimum recommended pitch for a shed is 2/12 for drainage, with 3/12–5/12 being the most practical range for a standard storage shed. Use the calculator above: enter your desired pitch and shed width to find the exact ridge height. A lean-to shed (single slope attached to a building) typically uses 2/12–4/12 — enough to drain away from the main structure.

What pitch for a shed? For a standard 10 ft × 12 ft shed with a 4/12 pitch: ridge height = (10 ÷ 2) × (4 ÷ 12) = 5 × 0.333 = 1.67 ft (about 20 inches). Rafter length (per side) = 5 ft × 1.054 = 5.27 ft (5 ft 3 inches).

Porch roof pitch

Most porch roofs are designed to match or complement the main house pitch. A standalone porch roof typically uses 3/12–5/12. Porch roof pitch should be at least 2/12 to ensure water drains away from the house and porch. Very flat porch roofs (under 2/12) require special waterproofing products and careful drainage planning.

Hip roof calculator

A hip roof has four sloping sides that all meet at the ridge or at a point. The pitch is the same concept as a gable roof — rise per 12 inches of run. However, hip roofs have both a main ridge length and hip rafter lengths (the diagonal corner rafters) that require additional calculation. For basic hip roof pitch: enter your desired pitch in Mode A above to get the slope factor, then multiply your total footprint area by the multiplier to find the roof surface area.

Lean-to roof slope

A lean-to (mono-slope, shed) roof is the simplest roof form — a single slope in one direction. Minimum lean-to slope: 2/12 for drainage. Recommended: 3/12–5/12 to allow water and debris to clear without being excessively steep. For an attached lean-to, the pitch is often limited by the existing wall height of the main structure.

Ridge height calculator — how to calculate roof ridge height

Ridge height = (building span ÷ 2) × (pitch fraction). For a 24 ft wide building at 6/12 pitch: (24 ÷ 2) × (6 ÷ 12) = 12 × 0.5 = 6.0 ft.

Ridge = (span÷2) × (rise÷12). Spot checks: 24 ft/6/12: 12×0.5=6.0 ✔ | 32 ft/8/12: 16×0.667=10.67 ✔

Roof pitch calculator — frequently asked questions

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This page covers roof pitch to degrees for every standard pitch (1/12–12/12), the slope factor/multiplier table, three calculator modes (pitch conversion, ridge height, roof area), minimum pitch requirements by roofing material, shed and porch pitch guide, and snow-country pitch recommendations. Use the free Roof Pitch Calculator above — enter your rise and run for instant degrees, slope factor, ridge height, and roof area.