How to Use the Light Steel Truss Member Length Calculator
When fabricating a light steel gable truss, knowing the exact length of the sloped top chord member ahead of time helps you cut material without waste. This calculator uses the Pythagorean theorem to find the sloped member length from just the span (total width) and the roof pitch.
The method multiplies the horizontal run - half the span plus any overhang - by the pitch to get the vertical rise, then finds the hypotenuse length as the square root of run squared plus rise squared. If your pitch is given as a ratio like 4:12, convert it to a percentage (33.3%) before entering it; if there's no overhang, just enter 0.
The result shows both the length of one sloped member and the total length needed across both sides and however many trusses you specify. When ordering material, it's good practice to add extra for splice laps and cutting losses beyond the calculated length.
Frequently Asked Questions
A roof pitch shown as a ratio, like 4:12, converts to a percentage by dividing rise by run and multiplying by 100 (4/12 x 100 = 33.3%). If you have an angle instead, enter tan(angle) x 100.
If the eave extends beyond the wall line, the sloped member's actual length needs to include that extra horizontal distance, not just half the span. Enter 0 if there is no overhang.