Roof Truss Calculator: Rafter Length, Count, and Cost

Your details

The total width of the building measured from outside wall to outside wall.
ft
How many inches (or cm) the roof rises for every 12 inches (or 12 cm) of horizontal run. A 6/12 pitch is a common moderate slope.
/12
Horizontal projection of the rafter beyond the wall plate on each side (eave).
ft
The length of the roof from one gable end to the other, measured along the ridge.
ft
Center-to-center spacing of roof trusses. 24 in (600 mm) is the most common for residential construction.
Estimated purchase price for one manufactured roof truss. Typical range: $75 to $500 per truss depending on span and complexity.
USD
Common rafter lengthMid-size project
16.77

Length of each common rafter from ridge to outside wall plate, including overhang

Rafter length unitft
Ridge board length40
Ridge length unitft
Total roof area (one side)670.8
Roof area unitft²
Number of trusses21
Material cost5,250
Labor cost0
Total project cost5,250
Material (trusses)5,250
Labor (installation)0

21 trusses needed, each spanning 16.77 ft.

  • Each common rafter (including overhang) runs 16.77 ft, which is also the length each manufactured truss needs to span.
  • One roof slope covers 670.8 ft² of sheathing; double that for the full deck area (1341.6 ft²).
  • At your chosen spacing you need 21 trusses. Adding one or two extras as spares is good practice.
  • Total estimated project cost is $5,250. Get at least three quotes from truss manufacturers and framing contractors before ordering.

Next stepYour pitch is in the common residential range (4/12 to 12/12), which is well-supported by standard manufactured trusses.

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