Calculate the length of common rafters with this free and easy online tool by entering a dimension for the roof width, selecting a pitch for the roof, and the thickness of the ridge. The results are organized in an easy to read form. They include :
- The length of the rafter.
- The rise of the rafter.
- The run of the rafter.
- Height of the scaffold
Rafter Calculator Instructions
Enter the value for the roof width (rafter span) in feet, inches, and fraction, inches and fraction, or use the inches box to enter a value in decimals if that is your preference. For example: 122.25 is equal to 122 1/4 and 10′ 2 1/4″. See the detailed instructions below for any further questions.
- If there will be no internet connection at the job site, then go ahead and open this page on a device such as a laptop or a smartphone in a location where there is an internet connection. Once this page is opened, the calculator will work without an internet connection.
- Take a direct measurement of the width of the roof. This must be from walls that are of equal heights. If they are not, then click here for the unlevel wall rafter calculator.
- Use the number boxes to enter the value in feet, inches, and fraction, inches and fraction.
- Then use the drop down to select a value for the fraction.
- For advanced users simply use the inches box to enter a decimal value.
- Use the blueprints to establish a pitch for the roof. Select a roof pitch.
- Determine a thickness for the ridge and use the drop down to select it.
The results are automatically fired as soon as any of the values are entered or altered. The length of the rafter is given from the long point of the ridge cut at the top down along the top edge the board to the same plumb cut on the rafter’s notch. The next result is the run. This is the horizontal measurement from the outside of the wall to the inside of the ridge. Then the rise is the vertical measurement from the top of the rafter on the outside edge of the plumb cut on the notch. This is also known as the HAP (height above plate). The scaffold is a value in inches that represents the vertical distance from the top of the HAP to the top of the walk board. Traditional layout methods when done properly reflect the accuracy of this calculator.