Calculate truss top chord length from span and roof pitch or rise, plus rafter length, overhang and truss count, in feet, inches, cm or meters.
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Top Chord Length Formula
This formula gives one side of a symmetric gable from the full span and the rise to the ridge centerline. It excludes overhang and ridge-board adjustments.
- Where TCL is the Top Chord Length
- B is the base of the truss
- H is the height of the truss
Inputs are converted to a common length unit; results use feet and include a nearest-1/16-inch representation where supported. Select Span or Rise for the inverse tasks. Rafter tasks also retain pitch, angle and optional ridge/eave calculations.
Run and rise refer to the ridge centerline. At fixed roof slope, a horizontal ridge thickness reduces the run by half that thickness; ridge-face length is (run − thickness/2) × slope factor. A horizontal eave adds overhang × slope factor. The overhang task also accepts an along-slope tail length.
The material task estimates ceil(building length / maximum truss spacing) + 1, including both ends with a possibly shorter end bay. Roof area includes both simple-gable sides and horizontal eaves but no ridge-end overhang. One roofing square is 100 ft²; bundle coverage is product-specific. The default three bundles per square is editable, and whole bundles round up after the entered material allowance.
These are geometry and quantity estimates, not structural design or final cutting dimensions. Heel geometry, birdsmouths, connections, bracing, member strength and project cutting allowances require the project design.
To calculate the top chord length, square half the base and square the height, add these two results together, then take the square root of the sum to get the top chord length.
What is a Top Chord Length?
Definition:
A Top Chord Length is a measure of the length of one side of the length of a truss chord used in building houses.
How to Calculate Top Chord Length?
Example Problem:
The following example outlines how to calculate a top chord length.
First, determine the base of the truss. In this example, the truss has a base of 20 ft.
Next, determine the height of the truss. In this case, the truss has a height of 15 ft.
Finally, calculate the Top Chord Length using the formula above:
TCL = √( (B/2)2 + H2)
TCL = √( (20/2)2 + 152)
TCL ≈ 18.02775638 ft
