Calculate your own roof truss

About the roof truss calculator and how we can help you

Our roof truss calculator will help you know the exact measurements for building or fixing your roof. Whether you are an individual building their own roof or a professional who needs to generate a drawing for themselves or their client, this roof truss calculator is for you

How to use the roof truss calculator?

All you need to do is add the numbers. The calculator will generate a printable professional drawing you can use while you work. A detailed explanation of how to use the calculator is down below. Please scroll down.

Roof truss calculator

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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Who is this truss calculator for?

This truss calculator is intended for individuals who build their own roofs, or professionals (contractors, architects, quantity surveyors, etc) who need to create a visual drawing of the truss they are building or fixing.

How does this truss calculator work?

The calculator has 3 parts:

  1. Input section where you need to add all measurements to create your drawing.
  2. Legend where you can see clearly each roof truss part and its name.
  3. Result drawing where you can see the dimensions of the trusses’ part, according to the measurements you input on part 1 of the calculator.

How to use this calculator in 4 easy steps?

Step #1: In order to produce the right roof design, you’d need to input 6 roof measurements.

  1. Length of the truss in inches
  2. Height of the truss in inches
  3. Width of the beams in inches
  4. Number of racks
  5. Overhang length in inches
  6. Rafter Birdsmouth Plumb in inches

Step #2: Click ‘Calculate’. That will generate a new drawing for you. Every time you’d change each one of the 6 measurements on step one and click ‘Calculate’ a new drawing is produced.

Step #3: Download and/or send the drawing to your email inbox. After clicking ‘Calculate’ a new form is open for you. Add your email address, and click ‘send PDF’ to send it straight to your inbox. In addition, you can click ‘open in a new tab’, which will open the drawing in a pdf format for you to download or print right away.

Step #4: Go to your local hardware store or anywhere you buy your building materials with this drawing and buy what you need to build your roof.

What kind of drawing will I get when using this truss calculator?

The output drawing has 5 sections:

General view section – This section shows you the general overview of your truss. In addition, you will see the following dimensions:

  1. Distance between your racks.
  2. Length of your truss with the length of the overhang.
  3. Length of your truss without the length of the overhang.
  4. Length of your overhang.
  5. Height of your truss.

Rafters section – This section will show your rafter’s exact measurements. The rafters generate the frame of your roof. In this section you will see:

  1. Rafters angles.
  2. Rafters length
  3. Rafters width
  4. Birdsmouth measurements.

A birdsmouth is a little cutout enabling the diagonal rafters to rest on the bottom rafter.

Racks section – This section shows the rack’s exact measurements. The racks are the horizontal beams connecting between the bottom and the top of the truss. In this section you will see:

  1. Racks length.
  2. Racks angles

Struts section – This section shows the exact measurements. The struts are the diagonal beams connecting between the bottom and the top of the truss. In this section you will see:

  1. Struts length.
  2. Struts angles

Dimensions details – This section shows you your inventory list needed for your truss. It shows you how many roof truss pieces you need for each kind of your rafters, racks and struts. They are all identified by their length. In addition, you’ll find at the button the total length of all your truss parts.

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 support 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.