Roof Truss Calculator
Plan your roof framing efficiently. Enter your building dimensions, roof pitch, and truss spacing to get the exact number of trusses needed, rafter length, and estimated material cost.
Total width of the building from wall to wall
Roof projection beyond the exterior wall
Price per prefabricated roof truss
How many roof trusses do I need for my building?
Calculate the number of trusses by dividing the total roof length by the truss spacing, then add one. For a 40ft long building with trusses every 2ft: 40 ÷ 2 + 1 = 21 trusses. The extra truss accounts for the first truss at the gable end. If the building has gable ends, you may also need two gable end frames separately.
What is the standard spacing for roof trusses?
The most common truss spacing for residential construction is 24 inches (2ft) on center. This provides adequate support for standard roofing materials. Some lighter roof systems use 4ft spacing, but this requires heavier framing members. Commercial buildings often use wider spacing (4-8ft) with steel trusses. Always consult local building codes for minimum requirements.
How do I calculate rafter length for trusses?
Rafter length is the hypotenuse of a right triangle formed by the roof pitch. For a 6/12 pitch: the roof rises 6in per 12in of run. Using the Pythagorean theorem: rafter per foot of run = √(6² + 12²) ÷ 12 = 1.118. For a 30ft span with 1ft overhang: half span + overhang = 16ft, rafter length = 16 × 1.118 = 17.89ft.
What affects the cost of roof trusses?
Truss cost depends on span length, pitch, complexity of roof design, local lumber prices, and whether special engineering is needed. Simple gable trusses are the most economical. Hip trusses, vaulted trusses, and those with complex overhangs cost more. Typical cost range: $75-$200 per truss for standard residential trusses, plus delivery and crane rental for installation.