How Much Roof Coating Do I Need?
In order to estimate how much roof paint you'll need, first you need to estimate the total square footage of your roof's surface. Just measure the length and width of each plane on the roof, including dormers. Then, multiply length x width to get the square footage of each plane. Simply add the square footage of each of the planes together to derive the total square footage of your roof.
For example, this flat roof has one
roof plane. Simply measure length (A) times the width (B): (include overhangs if any)
Example: A = 120' B = 100'
A x B = 120'
x 100' = 12,000 sq. ft. for the total square footage of the roof.
This gable roof has two planes. So, multiply length (A) times the width (B) to get the square footage for each side, then add the two sides together to determine the total square footage of the roof:
Side 1: 120' x 100' = 12,000 sq. ft. Side 2: 120' x 100'
= 12,000 sq. ft. Side 1 + Side 2 = 24,000 sq. ft. for the
total square footage of the roof.
Be sure to add 10% to all of your material totals for waste and spillage.
What if you have a steep roof?
To measure a steep roof, you will have to use an alternate method.
Steeper Roofs
Measure your house at ground level, then add in the roof's overhang for
greater accuracy. As an example, if the roof overhang is 12 inches, you'll
add 2 feet to the overall length and 2 feet to the overall width of the
house. This nominal square footage amount is then multiplied by the factor listed to the
right. 

Pitch 
Multiply by: 
4 in 12 
1.06 
5 in 12 
1.08 
6 in 12 
1.12 
7 in 12 
1.16 
8 in 12 
1.20 
9 in 12 
1.25 
10 in 12 
1.30 
11 in 12 
1.36 
12 in 12 
1.42 

Determining the pitch of your roof:
There are many methods of determining the pitch of your roof; the simplest is to measure it directly.
To Determine Roof Pitch Place a level against the roof as shown.
From the point where the level touches the roof, measure out 12 inches.
From this point measure the distance in inches from the bottom of the level to the roof.
This will be the first number in the roof pitch. the second number will always be 12.
(Print out Material Work Sheet) [worksheet.doc]
Here is an online roof calculator you can try [roof calc]
How To Paint Menu:
Wood Decks, Fences and Siding, Introduction
Cleaning Wood Decks, Fences and Siding
Refinishing Wood Decks, Fences and Siding
Reduce Attic Heat with Radiant Barrier Paint
Painting Ceilings with Insulating Paint
Painting Walls and Trim
Roof Coatings Application
Insulate RV and Mobile Home with Roof Paint
Paint Siding
Paint Stucco
Use a Roller with no mess
How to spray Paint
General Painting Tips
