Calculate Total Roofing Area
To calculate the total roofing area, you'll need to multiply the length and width of each section of the roof and then sum up those areas.
Here's the formula for calculating the total roofing area:
Total Area = Length × Width
Let's say you have a single rectangular section of the roof with the following dimensions:
- Length = 20 feet
- Width = 30 feet
To calculate the total roofing area for this section, you would use the formula:
Total Area = Length × Width
Substituting the given values: Total Area = 20 feet × 30 feet
Calculating the product: Total Area = 600 square feet
So, the total roofing area for this single rectangular section of the roof is 600 square feet.
What is Roof Pitch?
Roof pitch refers to the slope or steepness of a roof. It's an important measurement that factors into several aspects of your roof:
- Material Needs: The pitch directly affects how much roofing material you'll need. Steeper pitches require more material compared to shallow slopes.
- Structural Support: Roof pitch plays a role in determining the structural strength required for the roof frame. Steeper pitches need a more robust frame to withstand wind, snow, and other loads.
- Drainage: The pitch influences how water sheds off your roof. A proper pitch ensures efficient water drainage and prevents water from pooling, which can lead to leaks and roof damage.
Calculating Roof Pitch: There are two main methods
There are two main methods to calculate roof pitch, depending on what measurements you have readily available:
Method 1: Using Rise and Run (Ratio Method)
This method is commonly used and expresses pitch as a ratio (e.g., 4:12). Here's how it works:
- Measure the Rise: This is the vertical distance from the top of the roof deck (underside of the sheathing) to the highest point of the roof (peak).
- Measure the Run: This is the horizontal distance from the outside wall of your house to a point directly below the peak of the roof. Ideally, this should be half the total roof span, but confirm if your roof has a center peak.
- Calculate the Pitch: Divide the rise by the run and express the answer as a ratio (e.g., if your rise is 6 inches and run is 12 inches, your pitch is 6:12).
Method 2: Using Degrees
This method is less common but can be useful if you have the roof angle.
- Measure the Roof Angle: You'll need a tool like a level and a protractor to measure the angle between the roof deck and the horizontal plane.
- Convert Angle to Pitch: Use a trigonometry function (tangent) on your calculator to convert the angle in degrees to a pitch value (as a decimal).
What is Roof Multiplier?
The roof multiplier, also known as the roof pitch multiplier or pitch factor, is a value used in roofing calculations to adjust for the slope or pitch of the roof. It is used to convert the area of the roof's footprint (the horizontal area) to the actual surface area of the roof.
A table of these multipliers and angles is given below:
| Pitch |
Angle |
Multiplier |
| 1/12 |
4.8° |
1.003 |
| 2/12 |
9.5° |
1.014 |
| 3/12 |
14.0° |
1.031 |
| 4/12 |
18.4° |
1.054 |
| 5/12 |
22.6° |
1.083 |
| 6/12 |
26.6° |
1.118 |
| 7/12 |
30.3° |
1.158 |
| 8/12 |
33.7° |
1.202 |
| 9/12 |
36.9° |
1.25 |
| 10/12 |
39.8° |
1.302 |
| 11/12 |
42.5° |
1.357 |
| 12/12 |
45.0° |
1.414 |
Calculate Total Shingle requirements
After calculating the roof area, it is easy to calculate the number shingles bundle requirement.
Divide your total roof area by the shingle coverage area per bundle:
Estimated Shingle Bundles = Total Roof Area (square feet) / Shingle Coverage Area per Bundle (square feet/bundle)
A standard bundle of asphalt shingles typically covers 33.3 square feet of roof area.
For example
If your total roof area is 1000 square feet, the calculation would be:
1000 square feet / 33.3 square feet/bundle = 30.03 bundles (round up to 31 bundles).
Calculate Total Shingle bundles price
Once you have the estimated number of shingle bundles needed, calculating the total price is simple! Here's how:
Multiply the estimated number of shingle bundles by the price per bundle:
Total Shingle Bundle Price = Estimated Shingle Bundles * Price per Bundle
FAQs
How much roof area does a bundle of shingles cover?
A bundle of shingles covers approximately 33 square feet of roof area. Since a roofing square is 100 square feet, you'd typically need around 3 bundles of shingles to cover one roofing square.
How do i calculate how many shingles i need?
To calculate how many shingles you need:
- Measure Roof Area: Calculate the total square footage of your roof.
- Determine Coverage: Know that one bundle of shingles typically covers 33 square feet.
- Calculate Bundles Needed: Divide the total roof area by 33 to find the number of bundles needed.
Formula: