Project Tools

Roofing Calculator

Area Measurements
Nominal Roof Size (in sq. ft.)
Roof Pitch
Actual Square feet of House: sq. ft.
Number of Squares you Need:


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 Pitch

Rafter Pitch

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 - round to the nearest foot.

PitchMultiply By
4 in 121.06
5 in 121.08
6 in 121.12
7 in 121.16
8 in 121.20
9 in 121.25
10 in 121.30
11 in 121.36
12 in 121.42
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.)

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