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Roofing Calculator

To determine how many roofing squares you need for your project, enter the measurements —rounded to the nearest foot— into our pop-up calculator. A 10 percent waste allowance is automatically added to the total.

Tips on Measuring for Roofing

To accurately calculate the area of your roof, you must first determine its slope, or pitch. Roof pitches are described in terms of rise and run. The run is the distance from the outside edge of a perimeter stud wall to the center of the house. The rise is the distance from the top of a stud wall to the peak of the roof. A roof’’s pitch is determined by how much it rises for every foot it runs. Thus, a moderate 6 in 12 roof pitch means the roof rises 6 inches for every 12 horizontal inches it runs. A 12 in 12 pitch is a steep, 45-degree angle roof.

Roof Pitch

Use one of these three methods to calculate your roof’’s pitch. You’’ll need a level and a tape measure or ruler. Mark a spot on the bottom of the level, 12 inches from one end.

  1. On a ladder beside the roof, place the level a foot or so up the roof, hold it level, and measure from the 12-inch mark on the bottom straight down to the roof. If it measures 4 inches, you have a 4 in 12 pitch; 8 inches and you have an 8 in 12 pitch.
  2. On a ladder at the gable end of your house, place the level against the rake rafter (the one on the roof overhang) with the 12-inch mark on the rafter’s bottom edge. Now measure from the end of the level up to the bottom edge of the rafter. That is the roof’s rise.
  3. In the attic, place the level against a rafter with the 12-inch mark on the bottom of the rafter. Measure from the end of the level up to the bottom edge of the rafter. That is the roof’s rise.

Roof Area

Flat Roofs
If your roof is flat or has no more than a 3 in 12 pitch, you can calculate its total square footage by simply multiplying the length by the width.

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 a factor associated with the roof’’s pitch. (Note: These factors are listed to the right for your reference. They will be integrated into the calculator when you provide your roof pitch selections.)
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

Roofing Tips: Roof Slope & Style

There are two main categories of roofing: sloped and flat. A flat roof is considered to be a slope of 2/12 or less. The run always remains constant at 12 inches. A low slope roof is anywhere from 2/12 to 4/12. Conventional slope roof is 4/12, and anything more than 9/12 is considered steep. Steeper sloped roofs are considered more aesthetically pleasing and last longer, too. These benefits do not come cheaply though. A 12/12 roof can cost up to 50 percent more than a 4/12 roof. This is because a steep sloped roof requires a taller chimney and more lumber for framing. However, the end result may be well worth it as your roofing material is estimated to last up to 50% longer and will require less maintenance.

Roof styles or types are usually are predesigned by the builder of your home when you move in. They determine what kind of materials you can have on the roof because of their slope. You can have a flat roof, which is just like a long board across the top of your home. A gabled roof will be like two sides of a triangle. A shed roof is slanted down one way, either towards the left or right. A mansard roof is like a hat. Then a gambrel roof is like a barn roof. A mansard roof has a flat top with sides that lip over the top a little and then hang over the home.