The Truss Needed for Roof calculator computes the number of trusses needed for a roof based on the ridge length and spacing.
INSTRUCTIONS: Choose units and enter the following:
- (L) Ridge Length (see diagram)
- (oC) onCenter Truss Spacing
Truss or Rafter Count (TC): The calculator computes how many roof trusses are needed.
IMPORTANT NOTE: Always use trusses built to local code requirements with the proper certifications and markings.
The Math / Science
The number of trusses needed is based on the ridge length and the spacing. The formula for the number of trusses is:
TC = (L / oC) + 1
where:
- TC = Truss Count
- L = Ridge Length
- oC = Spacing between the trusses
Unless the ratio of L / oC is within 5% of an integer, the calculator rounds up. 
General Information
The user can enter the on-center figure for the spacing of the truss, but the system has put 24" as the default. An adder of one (1) is added to the truss count if the onCenter spacing does not come out close to even. This means that the spacing with the last truss may be less than the onCenter value, because engineering allows for trusses to be closer together without weakening the roof. Whereas, it is not permissible to space the trusses out further to make up the overage.
Pole Barn Calculator
The Pole Barn Calculator contains functions to compute the construction materials for a pole barn with concrete piers, a slab, wood framing, roof trusses for a normal gabled roof and metal panels and trim for the roof and siding.
- Gable Roof Metal: This estimates the materials needed for a metal roof for a simple gabled roof based on the roof dimensions.
- Purlins for a Roof: This computes the total number and length of purlins for a simple gable roof based on the ridge length of the roof, the roof pitch and the span of the roof.
- Trusses Needed for Roof: This computes the number of trusses needed for a roof based on the ridge length and spacing.
- Metal Siding for Gable Ends: This computes the metal siding materials (vertical panels) for a wall under a gable roof end based on the dimensions.
- Metal Siding for Gable End with Door: This computes the metal siding materials for a wall under a gable roof end based on the dimensions.
- Girts for a Building: This computes the number of rows of girts and their lengths for a building.
- Wall Beams for a Building: This computes the lengths beams for the outer wall of a building.
- Posts for a Building: This computes the number of vertical posts for a building based on dimensions and spacing.
- Rebar and Concrete in a Slab: This computes the total length and weight of rebar and the volume of concrete needed for a slab.
- Piers for a Building: This computes the number of piers for a building and the amount of concrete needed.
- Pole Barn Materials: This computes the top to bottom framing and roofing materials needed for a pole barn (see picture) based on a few dimension.
- Pole Barn Metal Roof and Siding Cost: This uses an estimated the linear feet of metal panels needed for a pole barn with a door way, and provides an estimated cost for the metal panels for the roof and siding based on a the dimension and cost per linear foot of panels.
- Corrugated Metal Paint or Coating Volume: This estimates the volume of paint or other coating (e.g., spray insulation) is needed for a corrugated surface.
IMPORTANT NOTE: Confirm all calculations with authoritative sources such as architectural drawings before risking health or wealth on the results of any calculator, and ALWAYS adhere to government approved building codes.
Roof Types
