Truss Calculator
Calculate truss dimensions, member lengths, and angles from span and pitch. Enter values for instant results with step-by-step formulas.
Formula
Rafter = sqrt((span/2)^2 + rise^2) | Rise = (pitch/12) x (span/2) | Angle = arctan(pitch/12)
Where span is the total width of the building, pitch is expressed as rise per 12 inches of run, rise is the vertical height at the peak, and rafter length is the hypotenuse of the right triangle formed by half the span and the rise.
Worked Examples
Example 1: Standard Residential Roof Truss
Problem: Calculate truss dimensions for a 24-foot span with a 6/12 pitch and 12-inch overhang for a 40-foot long building with 24-inch spacing.
Solution: Half span = 24 / 2 = 12 feet\nRise = (6/12) x 12 = 6 feet\nRoof angle = arctan(6/12) = 26.6 degrees\nRafter length = sqrt(12^2 + 6^2) = sqrt(180) = 13.42 feet\nRafter with overhang = 13.42 + 1 = 14.42 feet\nNumber of trusses = (40 x 12) / 24 + 1 = 21 trusses
Result: Rise: 6 ft | Rafter: 13.42 ft | Angle: 26.6 deg | 21 trusses needed
Example 2: Steep Pitch Garage Truss
Problem: Calculate truss dimensions for a 20-foot span with a 10/12 pitch and 18-inch overhang for a 24-foot garage with 24-inch spacing.
Solution: Half span = 20 / 2 = 10 feet\nRise = (10/12) x 10 = 8.33 feet\nRoof angle = arctan(10/12) = 39.8 degrees\nRafter length = sqrt(10^2 + 8.33^2) = sqrt(169.39) = 13.01 feet\nRafter with overhang = 13.01 + 1.5 = 14.51 feet\nNumber of trusses = (24 x 12) / 24 + 1 = 13 trusses
Result: Rise: 8.33 ft | Rafter: 13.01 ft | Angle: 39.8 deg | 13 trusses needed
Frequently Asked Questions
What is a truss and how does it differ from conventional rafters?
A truss is a pre-engineered structural framework made of triangulated members that supports a roof load and transfers it to the walls below. Unlike conventional stick-built rafters that rely on ridge boards and ceiling joists for structural integrity, trusses use a web of interconnected triangles to distribute weight efficiently. Trusses are typically manufactured in a factory and delivered to the job site ready for installation, which speeds up construction time significantly. They can span greater distances without interior load-bearing walls, giving builders more flexibility in floor plan design. Most residential construction today uses prefabricated trusses because they are cost-effective and engineered for specific load requirements.
What loads must a truss be designed to support?
Trusses must be designed for several types of loads including dead load, live load, wind load, and in some regions, snow load and seismic load. Dead load includes the weight of the roofing materials, sheathing, insulation, and the truss itself, typically ranging from 10 to 20 pounds per square foot. Live load accounts for maintenance workers, equipment, and temporary loads, usually 20 pounds per square foot for residential roofs. Snow load varies dramatically by region, from zero in southern climates to over 80 pounds per square foot in mountainous areas. Wind uplift can be a critical factor in hurricane-prone regions where trusses must resist being lifted off the walls. All loads must comply with the International Residential Code or local building code requirements.
Can I modify or cut into a prefabricated truss on site?
You should never cut, drill, or modify a prefabricated truss without written approval from a licensed structural engineer. Every member and connector plate in a truss is engineered to carry specific loads, and removing or weakening any component can cause catastrophic failure. Even drilling a single hole through a chord member can reduce its load-carrying capacity by 20 percent or more. If you need to run plumbing, electrical, or HVAC through a truss, consult the truss manufacturer for approved penetration locations or request trusses with pre-designed openings called chases. Some builders mistakenly cut web members to accommodate ductwork, which is extremely dangerous and often violates building codes. Always work with the truss engineer to accommodate mechanical systems during the design phase.
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Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.