Roof Pitch Calculator

What is Roof Pitch?

Roof pitch is the slope or angle of a roof surface, expressed as the ratio of vertical rise to horizontal run. It is one of the most important measurements in roofing and construction, affecting everything from material selection to drainage and aesthetic appearance. Our roof pitch calculator helps you quickly determine the pitch, angle, and rafter length for any roofing project.

Roof pitch is typically expressed in three ways: as an angle in degrees, as a percentage, or as a ratio in the form of x:12 (indicating how many inches the roof rises for every 12 inches of horizontal run). The roof slope calculator provides all three formats instantly.

How to Use the Roof Pitch Calculator

Using our roof slope calculator is simple. Enter the rise (vertical height) and run (horizontal distance) of your roof in inches. The calculator will instantly compute the roof angle in degrees, the roof pitch as a percentage, the pitch in x:12 format, the rafter length, and the pitch multiplier. The results update in real time as you adjust the values.

Roof Pitch Formulas

Roof pitch is calculated using right triangle trigonometry. The relationship between rise, run, rafter length, and pitch follows these formulas:

$$rafter^2 = rise^2 + run^2$$

$$pitch\ (\%) = \frac{rise}{run} \times 100$$

$$pitch\ (x:12) = \frac{rise}{run} \times 12$$

$$angle = \arctan\left(\frac{rise}{run}\right)$$

$$multiplier = \sqrt{\left(\frac{rise}{run}\right)^2 + 1}$$

Roof Pitch Categories

Roofs are generally categorized by their pitch:

• Flat roofs: 1/2:12 to 2:12 (4.2% to 16.7%) - require a small slope for water runoff
• Low pitched roofs: Below 4:12 (33.3%) - may require special materials to avoid leaks
• Conventional roofs: 4:12 to 9:12 (33.3% to 75%) - easiest to construct and safe to walk on
• High-pitched roofs: Above 9:12 (75%) - often require additional fasteners