Roof Area Calculator

Measuring the Roof’s Pitch

The incline or pitch of a roof can be easily measured with a level, tape measure, and a pencil. The roof’s pitch is the number of inches the roof rises in 12 inches. Therefore, mark off 12 inches on the level and place it down horizontally against the roof rafter.

Next, measure vertically from the 12-inch mark on the level straight up to the underside of the rafter, as illustrated below. That measurement is the number of inches the roof rises in 12 inches.

Some homes will have roofs with multiple pitches. Porches and dormer windows, for example, can have a different pitch from that of the rest of the house. For an accurate surface area measurement you should make note of these additional structures.

Using the table below, lookup the pitch/es and make a note of the number/s in the multiplier column. This multiplier number will be used to multiply the surface area calculation that SketchAndCalc™ will provide.

Search with the Roof Area Calculator

Accounting for dormer windows and other structures that might share a different pitch, the first step is to calculate the footprint of the roof, or the area it occupies.

Login to SketchAndCalc™ and select ‘Show Maps’ from the Menu.

Search the homes postal address from the map controls that appear in the top left corner.

When zoomed in, switch to satellite view.

Identify the roof’s structure. Regardless of complexity (multiple ridge lines, hips, valleys etc), if the roof has a single pitch or incline throughout you can simply draw the perimeter of the entire roof using SketchAndCalc’s™ line drawing tools.

TIP: Line length labels are displayed as you draw. If you find these labels obscure the view of the roof just switch them off from Menu > Settings > Application. You can also adjust the grid transparency and drawing line weight.

If the roof has multiple pitches, such as those found on dormer windows or porches you will need to draw these separately. After drawing the perimeter of the roof, add a new drawing layer with the plus (+) symbol found in the bottom right corner. Then proceed to draw the surface area of the roof that has a different pitch. Using dormer windows as an example, you’ll add a new layer after drawing each dormer.

Calculate the Surface Area of the Roof

You’ll notice as an area is drawn the area and perimeter results are displayed in the bottom right corner. With a single pitch roof you’ll have only one area result that relates to the entire footprint or perimeter of the roof. Both metric and imperial measurement systems are displayed in a popup menu over the results area.

Take your area result and multiply it by the pitch multiplier (or slope correction factor) found in the table above to arrive at the roof’s surface area. Now you’re ready to price out the materials.

For multi-pitched roofs simply add the areas of all common pitches together by toggling layer visibility from the summed layer (identified by the ‘eye’ symbol) at the left of the layers control.

Use the appropriate pitch multiplier for each totaled area calculated, then sum all the areas together.