The length of the truss


The height of the truss


Width of beam


Number of racks S



Rafter Birdsmouth Plumb



General view




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If you’re thinking about replacing your roof with a new one, you will need a roof truss calculator. This online truss calculator will determine the all-in cost of your truss based on key inputs related to the pitch, width and overhang of your roof. It will use the current cost of wooden rafters based on the average price found at home improvement stores.

The important point to keep in mind when you use your truss calculator is that every truss calculation is completely unique, and is based on the size of your roof and its specific dimensions. The truss is a framework consisting of rafters, posts and struts which supports your roof. As we will see below, there are several different types of designs, and this will impact the angles and designs of the overall truss.

When it comes to residential homes, there are almost as many different types of trusses as there are home designs, each with unique angles and dimensional attributes. Here are just some of the most popular types of truss frameworks:

  • Common
  • Studio vault
  • Tray vault
  • Cathedral
  • Room in attic
  • Parallel chord
  • Scissor
  • Mono
  • Porch

When using free online calculators, it’s important that you are using the right design for the right height. So always check if you can toggle between different types of trusses with your calculator – this will make it much easier to calculate all the angles, heights and dimensions. And, in turn, it will make it much easier to know which types of rafters and struts you will need and how to combine them for each height. When you go to a home improvement store or lumberyard, you want to make sure that you’re getting the right item with the right angle, the right height and the right dimensions!

Next, you need to perform a quick calculation based on just a few key inputs. You must calculate the following three variables:

  • Pitch – This is the incline of the roof expressed as a fraction. (Note: While pitch and slope are used interchangeably, they are not the same.)
  • Span (also known as gable width) – This is based on the total footprint of the house and refers to the distance between two exterior walls.
  • Overhang – This is the “extra” part that extends beyond the exterior wall of the home.

Depending on the complexity of your free computational tool, it may require you to enter details about rafter spacing (usually 16” on center), bridge type, height and board size. Just keep in mind that if the length of the board size is more than 20 feet, then you need to use a more expensive type of LVL board (and not a traditional pine board) for this longer length.

Finally, the truss calculator will compute the best dimensional method to connect the pieces of the truss with steel joints and a bridge. These steel joints are needed to support the overall truss. The more complex the truss framework is, the greater quantity of these joints will be required. The same thing is true for the bridge of the truss.

Putting all these calculations together, you will have a very useful tool that helps you to create the best solution possible for your home.