You need to replace the old shingles of your roof and it’s important to measure your roof to determine how many shingles you’ll need. You should know there are several different methods to measuring a roof.

How to Take Roof Ground Measurements

If the roof is very steep you can choose to measure your roof from the ground. Though this measurement will not be quite as precise as if you got on the roof and measured each section exactly, a roof measurement from the ground will provide you with numbers close enough to get a fairly accurate estimate.

1] The very first thing we need to obtain the ground level dimensions of the house, or its perimeter. Draw a diagram of your roof on a piece of paper. Label each section of the roof. You will write your measurements on the diagram to make it easy to make the roof’s size calculations.

2] You can use a measure tape to obtain the length and width of the outside house walls. Walk around the house and fill in your outline with your measurements making sure to account for overhang. If your house resembles a complex geometrical figure, such as several pieces of domino pieces next to each other on the table, then you can find the areas of each respective piece first, and then add the sums of their areas in order to get a total area in square feet.

3] Add all the sections square footage together. The sum of these numbers if your total square feet of the house, not the roof.

4] Converting Roof Area to “roofing squares”. In the roofing industry usually, things are simple and roofers work with small numbers, that is why you should convert your large numbers, expressed in square feet of roofing surface, to a simple number in expressed in the # of roofing squares. To calculate the square of a roof, take the number of square feet and divide it by 100.

5] Now you can determine the pitch of the roof. You have derived your 2 dimensional ground roof measurements and you will want to convert them into 3 dimensional roof measurements to account for the roof rise. This is a step in which a lot mistakes can be made, especially when dealing with a complex roof.

Pitch is calculated by the roof’s rise over its run. Measure from the edge of the roof over 12 inches (12 is the run) and see how many inches up the roof line is (this is the rise).

Get a slope multiplier from the chart below. Roof Pitch Slope Multiplier Chart:

  • 2 in 12 = 1.102,
  • 3 in 12 = 1.134,
  • 4 in 12 = 1.159,
  • 5 in 12 = 1.191,
  • 6 in 12 = 1.230,
  • 7 in 12 = 1.274,
  • 8 in 12 = 1.322,
  • 9 in 12 = 1.375,
  • 10 in 12 = 1.432,
  • 11 in 12 = 1.493,
  • 12 in 12 = 1.554.

6] Take the ground level square figure you came up with and multiply it by the appropriate slope multiplier. This will give you your roof square.

How to Take Roof Measurements – Measuring the Slope

1] Draw a rough layout of your roof. Divide the roof into manageable sections. This doesn’t have to be an exact sketch, but the closer to scale that you draw, the less room there will be for mistakes. Remember to account for skylights, chimneys, pipes and solar panels if you have any installed on your roof.

2] Measure and record your findings. Climb onto your roof and measure each section by its height and width. Record the measurements on your sketch of the roof.

3] Calculate the square footage of each rectangular section of your roof by multiplying each section’s length and width.

4] Finding the area of triangular sections is not as difficult as you might think. The area of a triangle is half the length times the width – (A=LxW/2). Use a tape measure to measure the length of the eave and the length from the center of the eave to the opposite point. Multiply these two numbers together and divide by 2. Mark this number on your diagram as the square feet for this section.

5] Add all the sections’ square footage together to calculate the total square footage of your roof.

6] Roofing materials are determined based on the number of “square” a roof is, not the number of square feet. To calculate the square of a roof, take the number of square feet and divide it by 100. Consult with a sales associate to determine the exact amount of shingle packages you’ll need.