Lean-to Roof Pitch Calculator – Easily Determine Your Roof Slope

A lean-to roof (also called a shed roof) is one of the simplest roofing designs, consisting of a single sloping surface. It’s popular for garages, sheds, and extensions because it’s easy to construct and allows water and snow to drain efficiently.

Before building or replacing a lean-to roof, knowing the roof pitch is essential. Roof pitch determines how steep your roof is, affects water drainage, and helps you calculate the required roofing materials. That’s where a Lean-to Roof Pitch Calculator comes in handy.

Formula to Calculate Roof Pitch in Degrees

The pitch in degrees can be calculated using the arctangent function:

$\text{Roof Pitch (°)}=arctan\left(\frac{\text{Rise}}{\text{Run}}\right)$

Formula to Calculate Roof Pitch Ratio

The pitch ratio is expressed as rise:run:

$\text{Pitch Ratio}=1:\frac{\text{Run}}{\text{Rise}}$

Formula to Calculate Roof Slope Percentage

The slope percentage shows the steepness as a percentage:

$\text{Slope (\%)}=\frac{\text{Rise}}{\text{Run}}\times 100$

Formula to Calculate Roof Surface Area

If the roof length is provided, you can calculate the sloped roof area:

$\text{Roof Area}=\text{Roof Length}\times \sqrt{{\text{Run}}^2+{\text{Rise}}^2}$

Example Calculation

Let’s assume:

• Roof Width (Run) = 10 ft
• Roof Rise = 4 ft
• Roof Length = 20 ft

Step 1: Roof Pitch in Degrees

$\text{Roof Pitch (°)}=arctan\left(\frac{4}{10}\right)\approx {21.8}^{\circ }$

Step 2: Roof Pitch Ratio

$\text{Pitch Ratio}=1:\frac{10}{4}=1:2.5$

Step 3: Roof Slope Percentage

$\text{Slope (\%)}=\frac{4}{10}\times 100=40\%$

Step 4: Roof Surface Area

$\text{Roof Area}=20\times \sqrt{{10}^2+4^2}\approx 215.4\text{ sq ft}$

Why Knowing Roof Pitch Matters

• Helps calculate roofing material requirements
• Ensures proper water drainage
• Impacts roof design and appearance
• Affects cost and labor estimates