Roof Slope Calculator

Knowing the slope of your roof is important for proper drainage, shingle installation, and material estimation. This Roof Slope Calculator helps you calculate the slope as a ratio (e.g., 4:12), in degrees, and as a percentage — all from simple inputs.

Formula 1: Roof Slope (Ratio)

The most common way to express slope is as Rise:Run.

$\text{Slope (Ratio)}=\frac{\text{Rise}}{\text{Run}}$

Formula 2: Roof Slope (Degrees)

You can also convert the slope to an angle in degrees using the arctangent:

$\theta =arctan\left(\frac{\text{Rise}}{\text{Run}}\right)$

Formula 3: Roof Slope (Percentage)

To express slope as a percentage:

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

Example Calculation

Let’s say:

• Rise = 6 ft
• Run = 12 ft

Step 1: Slope (Ratio)

$\text{Slope (Ratio)}=\frac{6}{12}=0.5\text{ or }6:12$

Step 2: Slope (Degrees)

$\theta =arctan\left(\frac{6}{12}\right)=arctan\left(0.5\right)={26.565}^{\circ }$

Step 3: Slope (Percentage)

$\text{Slope ( \%)}=\left(\frac{6}{12}\right)\times 100=50\%$

Final Answer:

• Slope (Ratio): 6:12
• Slope (Degrees): 26.565°
• Slope (Percentage): 50%

FAQs

1. What is roof slope, and how is it typically expressed?

Roof slope, or pitch, measures a roof's incline as the vertical rise over horizontal run. It's often shown as a ratio like 4:12 (4 inches rise per 12 inches run), aiding in drainage and material choices. This standard helps builders ensure proper water flow and structural integrity. (45 words)

2. How do you calculate or measure roof slope?

Measure rise (vertical height) and run (horizontal distance), then divide rise by run for the slope. Normalize to 12-inch run for ratio (e.g., rise in inches:12). Use a calculator for degrees (arctan) or percentage. On-site, employ a level and tape measure for accuracy. (43 words)

3. Why is roof slope important for homeowners and builders?

Roof slope ensures effective water and snow runoff, preventing leaks and damage. Steeper pitches enhance drainage but raise costs and wind risks; flatter ones fit modern styles but need extra waterproofing. It impacts energy efficiency, aesthetics, and code compliance for safe, durable roofs. (40 words)

4. What are common roof slopes for residential buildings?

Residential roofs often use 4:12 to 6:12 pitches for balanced drainage and cost with asphalt shingles. Low slopes under 3:12 suit flat designs needing membranes like TPO. Steeper 8:12+ pitches work in snowy regions for better load shedding and ventilation. (42 words)

5. What qualifies as a low-slope roof, and what are the minimum requirements?

Low-slope roofs have pitches below 3:12, typically 1/4 to 2:12 inches per foot for commercial or modern flat roofs. Codes require at least 1/4-inch-per-foot minimum for drainage to prevent ponding. Use specialized materials like EPDM for waterproofing. (41 words)